Cammer: The Pontiac OHC Six

With all the furor surrounding Ford and Chevrolet’s new 300+ horsepower V6 Mustang and Camaro, you would think hot six-cylinder engines were a new idea, at least in America. Not so — in 1965, about a decade after the demise of the Hudson Hornet and its “Twin H-Power” straight six, Pontiac introduced a sophisticated new overhead cam six-cylinder engine that promised V8 power and six-cylinder economy. This week, we look at the short life of the 1966-1969 Pontiac OHC six, Pontiac Firebird Sprint, and Tempest Le Mans Sprint.
1967 Pontiac Firebird Sprint hood badge
(Photo © 2006 Robert Nichols; used with permission)


John Zachary DeLorean was born in Detroit in 1925. Like many automotive executives of his era, he was a second-generation automobile man; his father, an immigrant from Alsace-Lorraine, had worked for a time as a millwright for Ford. As a teenager, DeLorean earned a scholarship to Lawrence Institute of Technology (now Lawrence Technological University) and, after a brief stint as an insurance salesman, took a job with the Chrysler Corporation. In 1952, he joined the Packard Motor Car Company, working with Forest McFarland, Packard’s chief R&D engineer, on projects like the second-generation Ultramatic transmission.

Packard was quite small by the standards of domestic automakers, with a deeply ingrained culture of unhurried Old World craftsmanship. Largely unencumbered by bureaucracy and nurtured by the ever-patient McFarland, DeLorean thrived, enjoying a level of autonomy rare in a conservative industry. When McFarland departed to join Buick in 1956, DeLorean was promoted to replace him as head of R&D.

If the Studebaker-Packard Corporation had been healthier, DeLorean might have enjoyed a fine career there. Unfortunately, by 1956, the company was staggering toward collapse. That summer, the Studebaker-Packard board decided to eliminate Packard’s own design and manufacturing facilities, consolidating development and production at the Studebaker plant in South Bend, Indiana. DeLorean started looking for other job opportunities.

He was soon contacted by Oliver K. Kelley, then the head of GM’s corporate Transmission Development Group (and one of the principal architects of the original Hydra-Matic and Dynaflow transmissions). Kelley made a concerted effort to recruit DeLorean and arranged a series of interviews for him, including a meeting with new Pontiac general manager Semon E. “Bunkie” Knudsen.

Although DeLorean was wary of GM’s top-heavy corporate culture and put off by Pontiac’s stodgy reputation, Knudsen convinced him that they could reinvent Pontiac and offered him a lucrative salary (around $14,000 a year, a handsome sum in the mid-fifties) to become the head of Pontiac’s new advanced engineering section.

DeLorean arrived at Pontiac on September 1, reporting to new chief engineer E.M. (Pete) Estes, whom Knudsen had recently recruited from Oldsmobile. DeLorean’s role was to develop new engineering concepts that might eventually find their way into production Pontiacs. As at Packard, he was given a free hand to explore novel and sometimes radical ideas, ranging from a rear transaxle with an unusual flexible driveshaft (later used for the 1961 Pontiac Tempest) to an experimental six with an unusual combination of air- and water-cooling.

1962 Pontiac Tempest convertible front 3q
Unlike most American compacts of its era, the 1961–1963 Pontiac Tempest did not use a six-cylinder engine. Most 1961-1962 Tempests were powered by a 196 cu. in. (3,186 cc) slant-four engine — essentially Pontiac’s 389 cu. in. (6,372 cc) V8 shorn of one cylinder bank. Buick’s 215 cu. in. (3,528 cc) V8 was optional in 1961-1962, but rarely ordered; fewer than 5% of buyers selected it. (Photo © 2009 Norm Stephens; used with permission)

By 1959, DeLorean had embarked on a new project: an advanced six-cylinder engine with a single belt-driven overhead camshaft.


We should pause here to explain a little bit about camshafts for the benefit of our less technically inclined readers. As you probably know, internal combustion engines produce power by burning both fuel and air. A four-stroke reciprocating piston engine — the type used by the large majority of cars and trucks — draws air and fuel into the cylinders, compresses it, ignites and burns it (either via an electrical spark or the heat of combustion), and then expels the burnt exhaust gases.

Reciprocating engines generally use spring-loaded poppet valves to admit air into the cylinders and expel the exhaust. In a four-stroke engine, each valve must open and close once for every two rotations of the engine’s crankshaft. When the valves open (timing), how far they open (lift), and how long they stay open (duration) all have a dramatic effect on how the engine performs.

Naturally, a reciprocating engine needs some mechanism to open and close the valves at appropriate times. This is generally accomplished with a camshaft, a metal shaft with a series of lobes that actuate the valves as the shaft rotates. The shape and position of those lobes (the cam profile) determine the valve timing, lift, and duration.

1966 Chevrolet Corvair camshaft
A typical mid-sixties automotive camshaft. This one is from a 1966 Chevrolet Corvair.

Figuring out where to put the camshaft presents a number of challenges for engine designers. The camshaft must be driven by the crankshaft and turn at one-half the crankshaft speed. The simplest way to achieve that is to mount the camshaft in the engine block, just above the crankshaft, and drive it with gears or a short metal timing chain. Until well into the 1970s, the vast majority of engines were cam-in-block designs.

Mounting the cam in the block is reasonably convenient for L-head (flathead) engines, where the valves are also in the block, but it poses some challenges for overhead valve (OHV) engines, which became predominant after World War II. As the name implies, an OHV engine mounts the valves in the cylinder head, which improves breathing and thermal efficiency. The problem is that it puts the valves some distance away from the crankshaft. Therefore, if the camshaft is in the block, it must actuate the valves remotely via pushrods and rocker arms. That, in turn, increases the inertia the camshaft must overcome each time it opens or closes the valves; the camshaft lobe must act on the mass of the pushrods and rockers, as well as the valve itself. That extra mass (and any slack in the linkage) limits how high and how quickly the engine can rev. At very high engine speeds, the valvetrain can develop more inertia than the camshaft can overcome, leading to a condition called valve float.

Pushrod valvetrain illustration © 2007 IJB TA at English language Wikipedia (CC BY-SA 3.0 Unported)
Diagram of a typical pushrod/rocker-arm layout of an overhead-valve engine. (Illustration: “Pushrod2” © 2007 IJB TA at English language Wikipedia (Ian Brockhoff?); resized, changed file format, and used under a Creative Commons Attribution-ShareAlike 3.0 Unported license)

These problems can be mitigated somewhat by minimizing the mass of the valvegear and using stiffer valve springs, but a simpler alternative is to mount the camshaft in the head rather than in the block. An overhead camshaft (OHC) engine needs no pushrods; depending on the position of the cam in the head, it can potentially eliminate rocker arms as well, greatly reducing the mass and inertia of the valvegear. The reduction in valvetrain mass not only enables the engine to rev higher, it increases the acceleration and deceleration rate of the valves. That allows the valves to be open longer (longer duration), which improves power, while minimizing the time the intake and exhaust valves are open simultaneously (overlap), which makes the engine smoother at idle and at low speeds than a pushrod engine with the same cam profile.

Inevitably, there are trade-offs. First, OHC engines tend to be taller than comparable pushrod engines, which can complicate packaging. Second, overhead-cam engines (and particularly engines with dual overhead cams) are usually somewhat heavier than pushrod engines and have a higher center of gravity. Third, an OHC V6, V8, or V12 requires two camshafts — four with dual overhead cams — while a pushrod engine can get by with one. Fourth, the camshaft still needs to be driven by the crankshaft, which becomes more complicated the further the camshaft is from the crank. OHC engines may use a long timing chain, a rubber belt, gears, or shaft drive to run the camshafts, any of which adds complexity and cost.

Those trade-offs made OHC engines quite rare in American-made cars until the 1980s. There were exceptions going as far back as 1904, but most were either competition engines or cost-no-object luxury cars like the DOHC Duesenberg Model J. The closest any American OHC engine came to mass production was the Wills Sainte Claire of the twenties, which accounted for fewer than 14,000 sales in an eight-year run. Other than the Pontiac OHC six, the only production overhead-cam engines in America between 1945 and 1970 were the short-lived Crosley CoBra and CIBA fours and the Willys/Kaiser Tornado engine, an OHC conversion of an older 226 cu. in. (3,622 cc) flathead six. The Tornado six was short-lived in America — Kaiser Jeep dropped it after 1966 except for certain military trucks — but it was used by Kaiser’s Argentine subsidiary, IKA, into the early eighties.

1958 Alfa Romeo Giulietta engine
Alfa Romeo was one of the few automakers of the fifties to adopt dual overhead camshafts; one cam operates the intake valves, one cam the exhausts. DOHC engines are more complex and more expensive than single overhead cam (SOHC) engines, but minimize the reciprocating weight of the valvegear and allow more efficient placement of both the valves and the spark plug.

European automakers were quicker to adopt overhead camshafts, although they did not become common for mass-market cars until the sixties. They eventually became nearly universal on European and Japanese engines as a way of extracting more power from relatively small displacements.


In the early sixties, six-cylinder engines were enjoying a modest resurgence in the American market. A decade earlier, buyers had shown a marked preference for the new breed of OHV V8s, leading some mid-priced automakers to abandon sixes entirely. Pontiac had dropped its venerable flathead six at the end of the 1954 model year and didn’t offer another six-cylinder engine until 1964. The sharp recession that began in 1957 sent the pendulum swinging the other way, leading to a new generation of six-cylinder compacts. Pontiac had bucked that trend with the four-cylinder Tempest, but it was clear that the division would need a new six eventually. That also presented an attractive opportunity to explore new ideas.

Both DeLorean and motor engineer Malcolm McKellar were intrigued with OHC engines both for their practical advantages (see the sidebar above) and for their rather racy connotations. Although overhead camshafts were very rare for American production cars, they were almost de rigueur for European racing engines and DOHC Offenhauser racing engines had been extremely successful at the Indianapolis 500 for many years.

1963 Jaguar E-type FHC engine
Jaguar was another firm adherent of overhead cams; its XK six (pictured here in a 1963 Jaguar E-Type fixed-head coupé) had dual overhead cams while Jaguar’s later V12 was SOHC. This engine had an enviable pedigree: In competition trim, it won the 24 Hours of Le Mans five times.

The direct inspiration for Pontiac’s OHC engines was the contemporary Mercedes big six, a 183 cu. in. (2,996 cc) engine found in the Mercedes 300 sedans and coupes and, in somewhat more highly tuned form, the 300SL sports cars. With its iron block and single overhead camshaft, the Mercedes engine was not as exotic as the twin-cam engines from Jaguar and Alfa Romeo, but it had an impressive competition pedigree and offered a fair compromise between power, fuel economy, and complexity. It became the conceptual starting point for Pontiac’s design work.


The major objections to overhead cams for mass-production engines had always been cost and complexity. Most gear-driven overhead cams were prohibitively expensive for non-racing use and unacceptably noisy to boot. Chain drive, used by most production OHC engines of the fifties, was somewhat simpler, but still entailed a relatively high level of mechanical noise, not to mention the challenges of maintaining proper chain tension and lubrication.

An intriguing alternative was using a cogged rubber belt, like the Gilmer belts used to drive mechanical superchargers. A belt is quieter than a chain or gear drive, weighs less and thus consumes little power, and requires no lubrication. Better still, it’s considerably cheaper than either gears or chains.

Pontiac OHC Six in a 1967 Firebird Sprint - front
The Pontiac OHC six’s timing belt did not normally require adjustment, but the tension could be adjusted if necessary by moving the front cover. Unlike some later OHC engines, the Pontiac cammer is not an interference engine. If the timing belt breaks, it will immediately stop the engine, but it will not normally cause valve or piston damage, a serious risk with some OHC layouts. (Photo © 2006 Robert Nichols; used with permission)

Belt-driven camshafts were not a new idea even then. In the mid-fifties, racing engine builders had begun experimenting with belt-driven DOHC heads, including a 1955 Cadillac V8 conversion. Although those early efforts were not very successful, they attracted the attention of the United States Rubber Company (later known as Uniroyal), which sensed a potentially lucrative new market; Uniroyal started developing automotive timing belts around 1956. Pontiac began its own experiments in 1959, initially using stationary engines.

Around the time the OHC six project began in earnest, the German automaker Glas introduced the 1004-S coupe, the first production car with a belt-driven OHC engine. The Glas engine, initially displacing 993 cc (61 cu. in.) and eventually expanded to 1,682 cc (104 cu. in.), proved durable and reasonably dependable, although Glas engineers hedged their bets by recommending timing belt changes every 25,000 miles (40,000 km).

The Glas engine was encouraging, but developing a timing belt adequate for a torquey big-bore six still presented a problem, particularly since McKellar was determined to find a belt that would last the useful life of the engine. Simple rubber belts weren’t strong enough or durable enough; reinforcing the belt with steel cords provided adequate strength, but the steel would rust and eventually weaken. Using stainless steel cords eliminated the corrosion problems, but was much too expensive and showed worrisome signs of fatigue at high mileage.

Pontiac’s eventual solution, developed in collaboration with Uniroyal engineer Richard Case, was a 1-inch (25-mm) wide, fiberglass-reinforced, neoprene-impregnated nylon fabric belt, which proved to be strong and durable, demonstrating minimal wear in high-mileage testing. Unlike some later automotive timing belts, it was not overly sensitive to dirt and oil, although Pontiac ultimately decided to keep it covered to protect it from snow and road spray.

Another of the bugbears of early overhead cam engines was the need for periodic valve lash adjustment. That, too, was unacceptable to Pontiac, whose divisional policy mandated hydraulic valve lifters (which needed no adjustment in normal use and prevented over-revving) for all engines carrying a factory warranty. Hydraulic lifters had never been seen as practical for OHC engines, but Pontiac developed a clever solution, a variation of a concept GM had developed and patented in the mid-fifties for pushrod engines. Although the OHC six’s camshaft was mounted almost directly above the valves, it actuated them through finger-type cam followers — essentially small rocker arms — each of which was pivoted on a small hydraulic sphere that functioned like a hydraulic lifter. The pressure exerted by the sphere served to maintain a constant zero valve lash, reducing mechanical noise and eliminating the need for routine valve adjustments without adding to reciprocating mass or inertia.

Pontiac OHC Six in a 1967 Firebird Sprint
The Pontiac OHC six had an iron block and head, but the cam cover (where the camshaft is actually mounted) and the timing belt cover are both die-cast aluminum, helping to keep total engine weight to 489 lb (222 kg). Note the location of the distributor; it’s driven by a shaft running along the side of the block along with the oil pump and fuel pump. (Photo © 2006 Robert Nichols; used with permission)

The rest of the engine was a study in compromise. The cast iron block was loosely based on that of Chevrolet’s 1962-vintage OHV six and shared the Chevrolet engine’s connecting rods and seven-main-bearing crankshaft. However, Pontiac extended the skirt below the crankshaft center line for greater rigidity, much as Ford had done with its old Y-block V8. (The deep skirt also allowed the use of cross-bolted main bearings, although these were specified only for the more powerful iterations.) Bolted to the right side of the block was an aluminum carrier for the accessory drive, including the gear-driven distributor and fuel and oil pumps. The accessory shaft sprocket was driven by the timing belt and did double duty as a belt tension adjuster.

The cast iron cylinder head used wedge combustion chambers with side-by-side valves like those of Pontiac’s V8s, but the camshaft was actually mounted in an aluminum cam carrier rather than in the head itself and had very wide lobes to minimize wear. The valves, shared with Pontiac’s V8s, were quite large: Intake diameter was 1.92 inches (48.8 mm) while exhaust diameter was 1.60 inches (40.6 mm), the biggest the ports would accommodate.

Despite its novel features, the Pontiac engine was more mildly tuned than were most of its European contemporaries. The basic version had a modest specific output of 0.72 hp/cu. in. (44 hp/liter), compared to 1.08 hp/cu. in. (65 hp/liter) for the big Mercedes six. On the other hand, the Pontiac engine was designed to be dependable and free of temperament, which could not necessarily be said for its more exotic British, German, and Italian rivals. It was not unlike Hollywood remakes of popular European films, retaining the basic plot of the original, but recast with familiar faces and a bigger effects budget.


Prototypes of Pontiac’s OHC six were running on test stands by the spring of 1962, but development and testing of the production engine was protracted and it was not production ready for another two years. That didn’t stop Mac McKellar from applying some of its concepts on a considerably larger scale.

For the past few years, Pontiac had been a major player in NASCAR competition, working surreptitiously with private teams to get around GM’s official no-racing policy. By 1962, NASCAR had become an arms race between the major automakers, each of whom fielded an array of increasingly specialized engines and equipment. Pontiac’s most recent salvo was the Super Duty 421, a ferocious 6,902 cc engine laughingly underrated at 405 gross horsepower (302 kW) with two four-barrel carburetors. It was essentially a hand-built engine, offered to the public only in tiny numbers for homologation purposes.

Despite its power, the Super Duty was hard pressed by the latest Chrysler and Chevrolet engines, particularly the new Chevrolet Mark II “Mystery Motor” that appeared in early 1963. To remain competitive in NASCAR, Pontiac would need something more.

McKellar’s solution was an overhead cam conversion of Pontiac’s 389 cu. in. (6,372 cc) V8, drawing on concepts developed for the OHC six. Where the six sacrificed outright sophistication in favor of lower production costs, the 389 had no such compromises; it had 32 valves, belt-driven dual overhead camshafts (using a more robust version of the six’s belt drive), a cross-ram intake manifold, and sequential fuel injection. Pontiac never released power figures for the DOHC engine, but it probably made well over 500 gross horsepower (373 kW).

Unfortunately, the twin-cam 389 never made it to the racetrack. In early 1963, GM chairman Frederic Donner issued a tersely worded memo reiterating the corporate ban on racing, adding that under-the-table participation would no longer be tolerated. Pontiac’s DOHC engine went back on the shelf, although the division continued to work on OHC V8s on an experimental basis. Toward the end of 1963, McKellar developed a simpler SOHC 421 with 16 valves and one belt-driven cam per bank, capable of some 620 hp (462 kW) with Tri-Power carburetion. This was followed in 1965 by a 24-valve SOHC version of the newer 428 cu. in. (7,008 cc) engine.

McKellar showed off the experimental engines to Hot Rod editor Eric Dahlquist in 1968, but none of the OHC V8s made it to even limited production. Forbidden to race, Pontiac had little need for them and the growing safety lobby had left GM management wary of fielding very powerful engines. A 500 horsepower (373 kW) OHC V8 would have been a provocative gesture as far as Washington was concerned and the GM brass was in no mood for provocative gestures.


While it originated in DeLorean’s Advanced group, the OHC six, unlike the V8s, was always intended as a production engine. Its prospects for production improved significantly in November 1961 when DeLorean was promoted to chief engineer, succeeding Pete Estes, who replaced Bunkie Knudsen as general manager. Although the six was destined to become the base engine in Pontiac’s A-body intermediate line, its first application was DeLorean’s most ambitious project to date: the two-seat Banshee.

The Banshee project, known internally by its styling code, XP-833, began in August 1963. Designed by Roger Hughet and Ned Nickles of the Advanced Design Studio, it was a compact fastback coupe, looking something like a miniature Corvette Sting Ray. To minimize tooling costs, XP-833 used a fiberglass body with a steel floorpan, although it borrowed most of its running gear from the new A-body Tempest. The OHC six was to be the base engine, although the second prototype was powered by a Pontiac V8. DeLorean conceived it as an inexpensive sports car, a competitor for the new Ford Mustang.

1964 Pontiac Banshee roadster side
Not counting the early non-running mockups, there were two Banshee prototypes: a coupe and a roadster. The coupe was powered by a base one-barrel OHC six, while the roadster was originally powered by a 326 cu. in. (5,340 cc) Pontiac V8, which probably would have been optional if the Banshee had made it to production. (Photo: “pontiac_banshee_2” © 2009 EvThoMcC; used with permission)

GM management was unenthusiastic about the Banshee, preferring Pontiac to instead join Chevrolet’s new F-body sporty-car program. Estes and DeLorean still believed the XP-833 was a viable concept, but they realized that the corporation would kill it if they continued developing it through normal channels, so DeLorean assigned Advanced Engineering chief Bill Collins to continue the project in secrecy.

In the summer of 1965, DeLorean was promoted to general manager of Pontiac. Seeing his opportunity, DeLorean had Collins show off the two fully finished XP-833 prototypes to senior management, along with a beautifully illustrated presentation that detailed the Banshee’s expected market position, tooling costs (well under $20 million), and projected sales (about 32,000 a year). With a starting price of $2,500, the Banshee would compete directly with the Mustang and would help to bolster Pontiac’s sporty image.

Unfortunately, Donner and GM president Jim Roche were not interested. They thought the XP-833’s lack of rear seats would limit its sales potential and worried the car would cannibalize sales of the more expensive and more profitable Chevrolet Corvette. DeLorean continued fighting for the Banshee until the spring of 1966, but Ed Cole, GM’s executive vice president, finally ordered him to forget it and develop a Pontiac version of the F-body, which became the 1967 Firebird.

To DeLorean and Collins’ great annoyance, not long after rejecting the XP-833 project, Roche and Donner approved production of the conceptually similar (and similar-looking) Opel GT, based on the European Opel Kadett sedan. The GT was roughly the same size as the Banshee, but it used a steel body and four-cylinder engines. To add insult to injury, it was sold in the U.S. through Buick dealers, not by Pontiac.


The failure of the Banshee did not mean the end of the OHC six, which finally went into production in the summer of 1965. That fall, it replaced a Chevrolet-derived 215 cu. in. (3,529 cc) pushrod six as the standard engine of the 1966 Pontiac Tempest/Le Mans.

In its initial form, the Pontiac OHC six displaced 230 cubic inches (3,769 cc), the same as the pushrod six used by the Chevrolet Chevelle/Malibu. The base engine, with a mild cam and a single-barrel Rochester carburetor, made slightly less torque than the Chevrolet engine — 216 lb-ft (293 N-m) to the Chevy’s 220 lb-ft (298 N-m) — but substantially more power: 165 gross hp (123 kW) to only 140 hp (104 kW) for the OHV Chevy. The OHC engine was not enough to make the Tempest a fast car, but it was a bit quicker than most contemporary American sixes.

The automotive press had known the OHC six was in the works for more than a year, but its arrival still made a great splash. Nearly every automotive magazine ran in-depth articles on the new six, speculating what it heralded for future Detroit engines. The buff books were particularly excited about the optional four-barrel version of the new engine, which Pontiac advertised as the answer to exotic European engines.

Pontiac OHC Six in a 1967 Firebird Sprint - left
The Sprint version of the OHC six had 10.5:1 compression, a big Rochester Quadra-Jet, and unique intake and exhaust manifolds with separate runners for each port. The 1967 version, pictured here, was rated at 215 horsepower (160 kW), giving it a nominal specific output of 0.93 hp/cu. in. (57 hp/liter), although that was in the old SAE gross rating system; we would guess that its net rating was somewhere between 150 and 160 hp (112 and 119 kW). (Photo © 2006 Robert Nichols; used with permission)

The four-barrel OHC engine had the same displacement as its more mundane sibling, but had new intake and exhaust manifolds, a hotter camshaft, and a higher compression ratio. In 1966, it was rated at 207 gross horsepower (154 kW) and 228 lb-ft (309 N-m) of torque, which was, as Pontiac advertising inevitably pointed out, more than many small-block V8s of the time. Chevrolet’s basic 283 cu. in. (4,638 cc) engine, for instance, was rated at only 195 hp (145 kW).

The four-barrel engine was marketed as part of a Sprint package that included stiffer shocks, side stripes, and other cosmetic details. Priced at $126.72, the Sprint package was available on any Tempest or Le Mans except station wagons. Pontiac marketed it as a European-style sports sedan, although most reviewers saw it as a sort of six-cylinder GTO. Naturally, the Sprint wasn’t as fast as the GTO, but its straight-line performance was more than adequate — 0-60 mph (0-97 km/h) took less than 9 seconds and top speeds of 115 to 118 mph (185 to 190 km/h) were possible. With less weight on the nose than a GTO, the Sprint also handled and stopped better. The hotter six was not particularly strong below 3,000 rpm, but it was tractable enough and many reviewers were entranced with its Jaguar-like growl.

1967 Pontiac Tempest Sprint front 3q
The Sprint package was available on any A-body Pontiac except wagons, but most went into coupes and two-door hardtops. It’s seen here on a 1967 Pontiac Tempest Custom convertible (with wheel covers from a ’62 Pontiac). (Photo: “1967 Pontiac Tempest Sprint OHC” © 2006 Mark Sevigny; used with permission)

Indeed, the Jaguar comparisons were tempting enough that Pontiac ad man Jim Wangers persuaded Doc Watson of Hurst Performance Products to install a Sprint engine and four-speed in a well-worn 3.8 E-Type. Hurst turned it over to Car and Driver, which found it somewhat slower than a healthy Series I E-Type, so Hurst added a trio of Weber carburetors and a few other shade-tree hot-rodding tricks that brought the engine to a claimed 315 horsepower (235 kW). Despite the magazine’s enthusiasm, the Pontiac-engined Jag didn’t inspire a raft of imitators, but it did attract a lot of attention, which was the point of the exercise. (The converted car was later purchased by Ford engineer Don Coleman, who substituted a 300 cu. in. (4,918 cc) Ford six for the Pontiac cammer.)

The publicity and favorable reviews were not enough to make the Sprint a runaway success. Total production for 1966 was fewer than 20,000 units, compared to nearly 97,000 ’66 GTOs. While the hot OHC engine was novel, it was not powerful enough to entice horsepower-crazed teenagers and the few customers interested in fuel economy in 1966 usually settled for the base engine. (Pontiac claimed the Sprint engine was capable of 20 mpg (11.8 L/100 km), but based on Popular Mechanics owner surveys, even the base engine was hard-pressed to return more than 17.5 mpg (13.4 L/100 km) in normal driving.) Even Car and Driver, for all its enthusiasm for the concept, reluctantly concluded that the V8 was the more sensible choice for the intermediate A-body. Despite the OHC engine, the Tempest/Le Mans Sprint was no sports sedan and many observers wondered if the hot six would do better in a smaller, lighter, sportier car.

1966 Pontiac Tempest Le Mans engine badge
The Sprint’s greatest rival was not any competitor, but Pontiac’s own 326 cu. in. (5,340 cc) V8. The 326 was thirstier and less sophisticated, but it offered 250 horsepower (187 kW) for less money than the four-barrel OHC six.


By the time the Tempest/Le Mans Sprint entered its second model year, Pontiac was busily readying the Firebird for its mid-year introduction. When the Firebird went on sale in late February 1967, the 165 hp (123 kW) OHC six was standard and the Sprint package as one of four engine options.

1967 Pontiac Firebird Sprint rear
As with the Tempest/Le Mans Sprint, the Pontiac Firebird Sprint package included side stripes, special badges, and stiffer shocks, along with the four-barrel OHC engine. It was very rare; we were unable to find exact figures, but we estimate that fewer than 5,000 ’67 Firebirds were Sprints. (Photo © 2006 Robert Nichols; used with permission)

On paper, the Firebird looked like a much better home for the Sprint engine than did the A-body Tempest, but the real-world results were less edifying. Although the Sprint engine was now rated at 215 horsepower (160 kW) and 240 lb-ft (325 N-m) of torque, most reviewers found the Firebird Sprint noticeably slower than the 1966 Tempest/Le Mans Sprint, particularly with the California emissions package. Part of the problem was the fact that the Firebird was not that much lighter than the Le Mans despite smaller dimensions; in fact, Car Life‘s well-equipped 1967 Firebird Sprint was actually 40 lb (18 kg) heavier than their 1966 Le Mans Sprint hardtop coupe. The Firebird Sprint handled marginally better than its V8 counterparts did, but it suffered all the suspension infirmities of all early F-bodies, including excessive wheel hop, a choppy ride, and a tendency to lose composure on uneven surfaces.

As with the Le Mans, the Firebird Sprint’s greatest problem was price. Although the four-barrel engine package was not particularly expensive, at $105.60, the 285 hp (213 kW) 326-HO actually cost about $10 less and mated better with the automatic transmission that most buyers preferred. Fewer than 25% of Firebird buyers opted for either OHC six.

Pontiac planned to drum up some interest with a special performance edition known as PFST (Pontiac Firebird Sprint Turismo), a Camaro Z/28-style homologation special for SCCA competition. Developed by engineer Herb Adams, the PFST used a modified version of the Sprint engine fitted with three Weber 40 DCN carburetors that protruded through the hood into a tall reversed scoop. The suspension was extremely stiff with stout anti-roll bars front and rear, giving excellent handling at the expense of a rather brutal ride. Pontiac let magazine testers drive the PFST prototype, but the new model didn’t make it to production. The triple Webers ran afoul of GM’s new ban on multiple carburetion and even after substituting a bigger Rochester Quadrajet, the modified engine was too loud to pass drive-by noise regulations.

Racing driver John Fitch, who had previously had a modest business selling modified Corvairs, developed his own tuned Firebird, also using the OHC engine. Unfortunately, the package was too expensive for most buyers. Fitch built only a handful of modified Firebirds, only one of which had the six-cylinder engine.

1967 Pontiac Firebird Sprint dash
Although most contemporary magazine reviewers tested Sprints with the four-speed manual, the vast majority of buyers opted for the optional automatic; either cost $184.31 more than the standard three-speed stick. The two-speed automatic (Buick’s Super Turbine 300, not a Chevrolet Powerglide) blunted the Sprint’s performance considerably; with automatic, the 0-60 mph (0-97 km/h) dash took around 12 seconds. (Photo © 2006 Robert Nichols; used with permission)


Going from advanced engineering chief to chief engineer and then general manager was a mixed blessing for John DeLorean. His increased authority also chipped away at his former autonomy — there was ever-increasing pressure to meet cost targets and adhere to conservative corporate policy. DeLorean’s clashes with senior management were seemingly endless, which made him many powerful enemies within the corporate hierarchy.

The OHC six eventually became another point of contention. DeLorean’s immediate superiors, GM group vice president Roger Kyes and executive vice president Ed Cole (who became GM president in the fall of 1967), were always unhappy about its high costs. Although Mac McKellar had done everything possible to minimize those costs, including sharing some parts with the contemporary Chevrolet six, the OHC engine was still more expensive to build than was its Chevrolet cousin. The OHC six also had higher warranty costs; while the timing belt itself was reliable, there were problems with premature camshaft wear and sticking valve lash adjusters. None of these issues was insurmountable, but they did nothing to win the confidence of an already skeptical corporate management.

For 1968, Pontiac stroked the OHC six from 3.25 to 3.53 inches (82.6 to 89.7 mm), bringing total displacement to the same 250 cu. in. (4,095 cc) as Chevrolet’s bigger pushrod six, introduced back in 1966. Increasing the OHC engine’s displacement was primarily intended to provide more torque for the heavier 1968 A-bodies and help the engine better cope with the new 1968 federal emissions standards, but Pontiac also added a new crankshaft with 12 counterweights rather than four, similar to the crank in the Chevrolet 250.

Pontiac claimed that the base OHC six now had 175 gross horsepower (131 kW), 10 hp (7.5 kW) more than before and 20 hp (15 kW) more than the pushrod Chevrolet six. Both the base and Sprint engines also had more torque: 240 lb-ft (325 N-m) and 255 lb-ft (346 N-m) respectively. However, the longer stroke made the Sprint engine noticeably less eager to rev, so its performance was not notably improved. Pontiac made a last effort to rectify that in 1969 by introducing two new camshafts for the Sprint engine. Cars with automatic again had 215 hp (160 kW), but slightly more torque, now 260 lb-ft (353 N-m); manually shifted cars, with more valve overlap, had 230 hp (172 kW) and 255 lb-ft (346 N-m).

Unfortunately, the interest of both buyers and the enthusiast press had by now mostly faded, so sales of the six continued to decline. That in turn made it harder than ever for Kyes and Cole to accept the OHC engine’s higher costs. A further problem was that the OHC engine was too tall to fit in the engine bay of the forthcoming second-generation Firebird without bulging the hood. As with the Banshee, DeLorean continued to fight for the OHC engine, but it was to no avail. DeLorean left Pontiac for Chevrolet in early 1969 and the OHC expired soon after that; starting in 1970, Pontiac would buy the cheaper 250 cu. in. (4,095 cc) Chevrolet six instead.

1967 Pontiac Firebird Sprint tail badge
The 1969 model year was the end of the line for both the one-barrel OHC six and the Sprint. The standard engine was now rated at 175 gross horsepower (131 kW); the Sprint had up to 230 hp (172 kW) with manual transmission. Sales were very low; we don’t have a precise figure, but it was probably fewer than 5,000 units. (Photo © 2006 Robert Nichols; used with permission)

DeLorean’s successor at Pontiac, F. James McDonald, was a production man, not an engineer, and shared neither DeLorean’s interest in technological novelty nor his penchant for battling management. Once the OHC six was dead, the OHC V8s were also canceled, as were a number of experimental derivatives of the six. Pontiac’s engineering focus shifted to emissions control; high-revving, high-performance engines seemed increasingly anachronistic.

The cancellation of the OHC six was unfortunate because less than five years later, the OPEC oil embargo sent Pontiac engineers scrambling to find smaller, more fuel-efficient engines. Unlike Buick’s resurrected V6, whose tooling had been sold to Kaiser Jeep and then to AMC, the tooling for the cammer was probably long gone by then, leading Pontiac to develop the undistinguished 301 cu. in. (4,942 cc) V8 instead. Had the OHC six survived, it probably would have done very well in the seventies. Even the Sprint might have found its niche, appealing to performance-minded buyers who couldn’t afford the insurance premiums on a GTO.


The next GM car to offer a belt-driven overhead camshaft was the Chevrolet Vega, which debuted in 1971. It spawned a Pontiac version, the Astre, in 1975, although Pontiac didn’t use the Vega’s 140 cu. in. (2,286 cc) OHC engine for long. For 1978, the Vega four was replaced by the 151 cu. in. (2,471 cc) pushrod “Iron Duke” engine, which Pontiac used well into the eighties.

By the late seventies, belt-driven overhead cams were becoming very popular, particularly on inexpensive four-cylinder engines. Sadly, many later timing belts were far less robust than Pontiac’s was and some OHC engines had an alarming tendency to eat valves if the belt snapped. By the beginning of the 21st century, concerns over belt longevity — and the high cost of changing a timing belt on a modern transverse engine — prompted a move back to timing chains. Timing belts are now becoming rare; even Honda has adopted chain drive for its more recent engines.

Hydraulic valve adjusters for OHC engines were slower to spread to other mass-market cars, although they began appearing on some luxury cars in the early seventies. They are now almost universal on OHC engines, mostly to help control exhaust emissions. (Having owned several cars that required valve adjustments every 15,000 miles (24,000 km), the author also considers hydraulic lash adjusters a tremendous convenience.)

It’s unfortunate that the Pontiac OHC six became something of a dead end. The Sprint, in particular, offered a combination of decent power, modest weight, and respectable fuel economy that was not seen again on an American car for years afterward. Along with the turbocharged Oldsmobile Jetfire V8 of a few years earlier, it was among the most sophisticated American engines of its era. The OHC six had its faults, but none of them was crippling and most can be rectified today with a competent rebuild and regular oil changes.

The stillborn OHC V8s are even more tantalizing. Even if they had made to production, it would probably have been on a very limited basis, like the earlier Super Duty engines. However, if DeLorean and McKellar had gotten their way, the performance engines might well have spawned mass-production derivatives, if only for homologation purposes. It’s easy to understand why the prospect of bolt-on OHC heads for the GTO had buff book editors salivating.

Unfortunately, it was not to be. Only one of Pontiac’s OHC V8 engines made it to the street, a SOHC 421 that Mac McKellar received as a parting gift on his retirement in 1982. Installed in McKellar’s 1963 Grand Prix, it was a fearsome sleeper, a sad — and potent — reminder of opportunities missed.



A little over a year after this article was written, we learned of the death of Malcolm McKellar, who passed away on April 8, 2011. He was 90 years old. McKellar outlived his former boss, John DeLorean, by six years: DeLorean died in 2005 at the age of 80.


Our sources on the development of the “Cammer” included Jim Black, “Buyer’s Guide: 1966-’67 Pontiac Le Mans Sprint,” Hemmings Muscle Machines June 2009, and “Pontiac’s Fantastic Six,” (n.d., The Pontiac-Oakland Club Overhead Cammers Chapter website, www.overheadcammerschapter. 150m. com, accessed 10 April 2010); Ray T. Bohacz, “Mechanical Marvels: Chain Gang: Exploring Camshaft Drive Mechanisms,” Hemmings Classic Car #12 (September 2005), pp. 66–69; Marc Cranswick, Pontiac Firebird – The Auto-Biography (Car & Motorcycle Marque/Model) (Poundbury, Dorchester: Veloce Publishing, 2003); Christopher M. Drew, assignor to General Motors Corporation, “Rocker Adjusting Mechanism,” U.S. Patent No. 2,934,051, filed 28 May 1956, published 26 April 1960; John Ethridge, “Tempest’s New Cammer!” Motor Trend Vol. 17, No. 9 (September 1965), pp. 40-44; Kit Foster, “1967 Pontiac Firebird Sprint: OHC from John Z’s PMD,” Special Interest Autos #150 (November-December 1995), reprinted in The Hemmings Motor News Book of Pontiacs: driveReports from Hemmings Special Interest Autos, ed. Terry Ehrich (Bennington, VT: Hemmings Motor News, 2001), pp. 118-127; John Gunnell, Standard Catalog of GTO, 1961-2004 (Iola, WI: Krause Publications, 2003); Wick Humble, “1961 Pontiac Tempest: But cars aren’t supposed to have curved driveshafts,” Special Interest Autos #48 (November-December 1978), reprinted in The Hemmings Motor News Book of Pontiacs , pp. 78-86; Roger Huntington, “Much More Muscle for 1966,” Car Life Vol. 12, No. 10 (November 1965), pp. 57–60; Don Keefe, “Department X: The 1964 OHC-6 Banshee Coupe,” High Performance Pontiac November 2001, pp. 38–41, and “Grand Performance: Pontiac’s luxurious muscle car: the 1964 Grand Prix,” Special Interest Autos #195 (June 2003), pp. 24–31; Jeff Koch, “John Z. DeLorean: Thoughts and memories from the immortal creator of the GTO, 30 years later,” High Performance Pontiac February 1994, pp. 22-23; Alex Markovich, “New Cars: What’s Ahead in 1966?” Popular Mechanics Vol. 124, No. 4 (October 1965), pp. 96–100, 219–220H; George Mattar, “1966 Progressive Pontiac: PMD’s advanced overhead-cam-six Tempest for 1966,” Hemmings Classic Car #7 (April 2005), pp. 46–53; “McDonald, F. James,” Generations of GM History, GM Heritage Center, history.gmheritagecenter. com/wiki/index.php/ McDonald,_F._James, accessed 11 September 2015; Mike Mueller, “When Less Was More: Pontiac Overhead-Cam Six-Cylinder,” American Horsepower: 100 Years of Great Car Engines (St. Paul, MN: MBI Publishing Company, 2006), pp. 117-121; Eric Nielssen, “Pontiac’s New SOHC Six,” Car and Driver September 1965, reprinted in Car and Driver on Pontiac 1961–1975, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1986), pp. 36-38, 59; “1966 at GM: Plastic Grille, OHC 6 Among Pontiac Innovations This Year,” Car Life Vol. 12, No. 10 (November 1965), pp. 50–52; Jan P. Norbye, “How Hot Can a Six Get?” Popular Science Vol. 188, No. 6 (June 1966), pp. 70-73, and “Sensational New OHC Six from Pontiac,” Popular Science Vol. 187, No. 2 (August 1965), pp. 37-41; Jan P. Norbye and Jim Dunne, Pontiac 1946-1978: The Classic Postwar Years (Osceola, WI: Motorbooks International Publishers & Wholesalers, 1979); the Old Car Brochures website (; Pontiac Motor Division of General Motors Corporation, “Four leading car experts report on Pontiac’s Break Away Squad for ’69—” [brochure], September 1968]; Jim Schild, Original Pontiac Firebird and Trans Am 1967-2002: The Restorer’s Guide (St. Paul, MN: Motorbooks, 2007); and J. Patrick Wright, On a Clear Day You Can See General Motors: John Z. DeLorean’s Look Inside the Automotive Giant (Chicago, IL: Avon Books, 1980).

Additional technical details came from Ray T. Bohacz, “Mechanical Marvels: Henry’s Bent Eight: The 1954 Ford V-8 engine,” Special Interest Autos #195 (June 2003), pp. 54–56; Doc Frohmader, “Pontiac OHC” (2006,, www.webrodder. com, accessed 14 April 2010); Donald J. Hoffman, 1966, “Hydraulic Lash Adjuster,” U.S. Patent No. 3,273,548, filed 29 September 1965 and issued 20 September 1966; Michael Lamm, “Fishbowl: 1955 Ford Crown Victoria Skyliner” from Special Interest Autos #37 (November-December 1976), reprinted in The Hemmings Motor News Book of Postwar Fords: driveReports from Special Interest Autos magazine, eds. Terry Ehrich and Richard Lentinello (Bennington, VT: Hemmings Motor News, 2000), pp. 48–55; and Jan P. Norbye, “Comparing the Compacts: Valiant • Falcon • American • Chevy II,” Popular Science Vol. 187, No. 5 (November 1965): 90–94, 184.

Information on Pontiac’s other OHC engines came from Eric Dahlquist, “Big Medicine from Pontiac,” Hot Rod March 1968, pp. 30-35; Don Keefe, “Dept. X: Malcolm ‘Mac’ McKellar’s 1963 Grand Prix is powered by the world’s only surviving OHC 421 Pontiac V8!” High Performance Pontiac October 1990, pp. 30-31; Rocky Rotella, “Pontiac V8 Engines – Photographing Legends,” High Performance Pontiac March 2010, www.highperformancepontiac. com, accessed 10 April 2010; and Bob Wicker, “An Interview with Herb Adams” (January 2010, Pontiacs Online, www.pontiacsonline. com, accessed 10 April 2010).

Additional background information on other American OHC engines came from the Auto Editors of Consumer Guide, Encyclopedia of American Cars: Over 65 Years of Automotive History (Lincolnwood, IL: Publications International, 1996); Ray T. Bohacz, “Mechanical Marvels: Only in a Jeep: The 1962 Willys Overhead Camshaft 6-cylinder Engine,” Special Interest Autos #187 (January-February 2002), pp. 54–56; Jim Bollman, “Crosley Engine Family Tree,” Crosley Automobile Club, n.d., crosleyautoclub. com/EngineTree/ Crosley_Eng_Tree-1.html, accessed 24 May 2020; John R. Bond, “Willys 4wd Wagoneer,” Car Life Vol. 10, No. 3 (April 1963), pp. 54–61; “Evolution of the Wills St. Claire” (2008, Wills Ste. Claire Museum, www.willsautomuseum. org, accessed 11 April 2010); Pat Foster, “The Other Overhead-Cam Six,” Special Interest Autos #150 (November-December 1995), reprinted in The Hemmings Motor News Book of Pontiacs, p. 123; John Gunnell, ed., Standard Catalog of American Cars 1946-1975 Revised 4th Edition (Iola, WI: Krause Publications, 2002); Roger Huntington, “Will Camshafts be Kicked Upstairs? Progress Report on Overhead Cam Development, Yesterday, Today or Tomorrow?” Motor Trend Vol. 16, No. 7 (July 1964), pp. 56-57, 90-92; and Maximiliano Pallocchini, “Tornado: Historia, creación y origenes,” Club Amigos del Torino, 3 August 2012, www.clubamigosdeltorino. index.php/ component/ k2/ item/ 5-tornado-historia-creacion-y-origenes.html, accessed 4 August 2015.

Some information on the Red Baron came from Moldy Marvin, “The Tom Daniel Story” (2004,, www.ratfink. org, accessed 11 April 2010).

We also consulted the following period road tests: Jim Dunne, “’66 Tempest: A tiger in performance, a dog on gas,” Popular Mechanics Vol. 125, No. 5 (May 1966), pp. 82-84, 230, and Bill Hartford, “A Rip-Roarder…with Rattles,” Popular Mechanics Vol. 129, No. 2 (February 1968), pp. 96–98, 208; John Ethridge, “OHC in a Tempest,” Motor Trend Vol. 18, No. 1 (January 1966), pp. 46-49, and “Sporty Specialties: Cougar & Firebird,” Motor Trend Vol. 19, No. 5 (May 1967), pp. 34-37, 41-42; “Pontiac Tempest Sprint,” Car and Driver December 1965, and “Pontiac Le Mans Sprint,” Car and Driver February 1967, reprinted in Car and Driver on Pontiac 1961–1975; “Pontiac Tempest Sprint & GTO: It’s Still….Six for the Money and Eight to Go!” Car Life May 1966, reprinted in GTO Muscle Portfolio 1964–1974, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1998); and “A Brace of Birds: The Sprint and the 400 from among Pontiac’s Five Firebirds,” Car Life August 1967, John Ethridge, “Fire Breathing Bird…first of the spring from Pontiac,” Motor Trend Vol 19, No. 3 (March 1967); “Firebird Sprint: The Sensible Supercar,” Cars December 1967; Steve Kelly, “How Do You Say ‘PFST’?” Motor Trend Vol. 19, No. 7 (July 1967); “Look What They’re Doing to the Firebird Now,” Car Life April 1968; Jon McKibben, “Fitch Firebirds: With the Corvair market diminishing, John Fitch finds another car to improve,” Road & Track April 1968; and “Pontiac Firebird Sprint,” Road & Track June 1967; and Sergio D’Angelo and L’Editrice Dell’Automobile LEA, “Pontiac Firebird Hardtop Coupe,” World Car Catalogue 1969, all of which are reprinted in Firebird and Trans-Am Muscle Portfolio 1967–1972, ed. R.M. Clarke(Cobham, England: Brooklands Books, Ltd., 1998).

We later updated the article to note the passing of Malcolm McKellar, based on information from Richard Lentinello, “RIP, Mac McKellar,” Hemmings Daily, 2 May 2011, blog.hemmings. com, accessed 15 June 2011; and Paul Stenquist, “Malcolm McKellar, Pioneer of the Pontiac Overhead-Cam Engine,” New York Times 3 May 2011, wheels.blogs.nytimes. com, accessed 15 June 2011. We confirmed McKellar and DeLorean’s dates of birth and death via the Social Security Death Index.



Add a Comment
  1. Great article Aaron! Milt Schornack of Royal Bobcat fame had some good words concerning the OHC six in his book. It appears they did some testing with headers and a tri-power setup on the sprint six engine. It would be quite the sleeper if it weren’t so loud.

    1. Pontiac did some similar experiments — the PFST project, developed by Herb Adams, used three Webers and headers. It was a pretty good setup, but it was too noisy to pass muster, and GM had banned multiple-carburetor setups.

      (Once interesting side note is that McKellar’s engine guys tried to create a common baseplate for the Tri-Power set-up so they could tell the corporation it was a single six-barrel carb. It didn’t work, though.)

  2. Grandpa was a Pontiac man for years – I was carsick numerous times as a young boy in the back seat of his 1966 Tempest OHC-6/Powerglide four-door.

    Years later, the car ended up in my hands, but the top end of the six had already died – I pulled the engine and replaced it with a Chevy 350 and THM350. Always loved that car – the dash was jewel-like with its deep-set gauges, and I always marveled at the “Wondertouch” power steering and brakes.

    The car is long gone, but I still have the OHC valve cover up in the attic somewhere – always thought it was a true piece of automotive art.

    1. Top-end oiling was a persistent problem with these engines when they were new — inadequate flow to the cam covers, particularly when the oil was dirty. I’m told that with modern oil and regular changes, it’s not a big deal, but it killed a lot of cammers when they were new(ish).

  3. How does an engine designed by (presumably) capable, experienced engineers make it into production with a design flaw like this?

    1. Mac McKellar actually took pains at the design stage to reduce camshaft wear; the lobes were twice the normal width, for example, in an effort to reduce surface pressure. However, hand-assembled test engines may not reveal issues that crop up with assembly-line engines owned by people who only change their oil once a year.

      As I understand it, the camshaft damage to the ’66 and ’67 engines was usually caused by one of three things:

      1) Incorrect machining of the metering hole in the restrictor that that controls the flow of oil to the camshaft journals. A lot of ’66 and ’67 engines came through with too large a metering hole, effectively reducing oil pressure to the cam and lash adjusters. This problem could be exacerbated by an incorrectly machined or clogged primary oil passage (the line through which oil flows to the cam cover), which could happen with infrequent oil changes or poor-quality oil.

      2) Too rough a finish on the contact area of the cam follower, where the follower actually touches the cam lobe, scuffing the cam.

      3) Broken retaining clips. The ’66 and ’67 engines used little metal spring clips to hold the lash adjuster to the cam follower during assembly. This was just an assembly-line convenience; once the cam cover is assembled, it’s not necessary. However, they just left the clip in place on the assembled engines, which would occasionally break when the engine was running, damaging the cam and/or valves with the pieces. The later engines omitted the clips, and simply removing them from the 230 will avoid the problem.

      For the most part, these were manufacturing/assembly issues, rather than design problems. Without talking to old Pontiac engineers, I don’t know why they weren’t fully resolved until the ’68 model year; if they’d been taken care of in the first few months of production, I’d file them under “teething problems.” I assume it comes down to the fact that design engineers don’t control production, and vice versa, as happened with the con rod breakage on the Fiero engines years later. (In that case, Saginaw foundry division was aware of the metallurgical problems, but they had no incentive to fix them.)

  4. This engine should have been an option in the 73-74 Ventura GTO. With an appropriate suspension and steering it would have been an excellent road car for the time and sales would have exploded during the first oil embargo.

    1. If GM had let Pontiac keep that engine past 1969, it should have surpassed the pushrod Chevy I6 until the end of the 70’s. Had the people at GM known there was going to be a oil embargo in 73 it would have been a more perfect replacement for the Chevy I-6.

  5. Can anyone help with a diagram of the timing marks for a 68 Pont Firebird 6 ohc engine. It would be greatly apprecceiated. Thanks.

  6. I have a OHC 6 without a Z (code) build date I think is L076 (DEC. 7th 1966) But can not find any code starting with a Z? I was told this engine was never loaded into a car or frame and was sent to a school for testing? Do you thoink there would be any truth to this? Thank you Rick

  7. Needing a diagram of a 1969 250 OHC 6 timing marks

  8. I thought the cammer poncho was awesome,–especially the Sprint, and I wonder–do blue prints/photos exist for the never-produced DOHC 389? Or even the SOHC 421 & SOHC 428? The tri-power OHC-sprint? Taking a page out of Govt., I wonder what “vices” those jerk-Globalist(imo) Board Members of GM had–evidently none that Delorean was able to exploit. I mention this because Pontiac is no more but for idiots that didn’t want to “ruffle” Govt. feathers, like the moribund Roach and the drooling Donnor-Dumber–two killers of Pontiac-Power, and Legend.

    1. I assume the blueprints for those engines still exist in the files somewhere (certainly for the SOHC — as the conclusion mentions, Mac McKellar ended up with one of the prototype engines). It’s possible some of the prototypes are in the Heritage Center, along with other abortive GM engines like the SOHC Cadillac V-12, but I haven’t checked.

      It’s easy to understand why the SOHC and DOHC V-8 projects ended up not going anywhere, regrettable as it may be. Pontiac already had engines more powerful than senior corporate management thought was prudent; the division didn’t have a NASCAR program where a hot SOHC 421/428 would be really useful; and price escalation and insurance rates were already making the really hot cars unaffordable to most of the kids who wanted them. And that’s without even getting into the emissions certification issues. If the SOHC/DOHC engines had made it out of experimental, they probably would have been roughly as attainable as the Ford SOHC 427 or Chevy’s early Z-11 427 “Mystery Engine.” For the street, a Ram Air 428 or 455 would have been a lot cheaper and probably more practical.

      Still, I would be lying if I said I didn’t find the idea of a Trans Am 303 with overhead cams intriguing…

  9. I need a starter for a 1967 firebird,4.1 liter overhead cam sprint with a two speed power glide trans. or a gm part number, picture anything thanks in advance Tony

  10. I’m afraid I really don’t know — sorry!

  11. GM UK (Vauxhall) introduced a belt driven SOHC four engine in 1968, using some design cues from the Pontiac 6, the camshaft in an aluminium housing and large followers, but with solid lifters. Very few European engines had hydraulic lifters then.
    However it was slanted 45 degrees, more like half a V8, although it helped it fit under hoods more easily.
    It wasn’t a great design, no more refined or efficient than old fashioned ohv engines from contemporary Ford or BMC offerings, and nor easy to work on either.
    I suspect some aspects of its design were influenced by Pontiacs development work, can you verify or deny this?.


    1. Roger,

      I honestly don’t know — I haven’t looked closely at Vauxhall’s behind-the-scenes history in that era. If I find anything out in that regard, I’ll comment here.

      1. If you haven’t already you should check out Vauxpedia that has lots of useful information on what Vauxhall was up to in terms of development.

  12. I have a 4.1 ltr ohc motor and two speed powerglide trans up for grabs I pulled out of my 69 firebird. located in ct

    1. Did it sell?

      1. Hey Charles,

        I generally advise caution when it comes to publishing your email address and/or phone number online — if you’re sure you want to do that, I’ll approve it, but I take no responsibility for the potential consequences or flood of spam.

  13. Can a base 67 Firebird 6 cylinder ohc engine be modified to be a sprint engine? If so, what reference is available to complete the conversion?

    1. I’m not qualified to advise anyone on modifying engines — sorry!

    2. I would imagine higher comp pistons and sufficient flowing manifolds along with a hipo carb setup.

  14. I just picked up the base overhead cam 6 engine from a 68 Firebird. My Dad worked at the Pontiac dealership when these cars were new. He said the only one that gave cam trouble were the ones the older people had. He any younger people that drove them kept them revved up high enough I guess to keep the cam lubed.

  15. I just purchased a ’68 firebird for restoration. I need tghe 6 cylinder overhead cam motor for it. Any for sale?

    1. I don’t sell parts, cars, or engines, sorry!

    2. I have a original 66 from a tempest if your interested

    3. i have a ohc 6 from 67 Lemans, complete for rebuild except quad carb, will look at offers. thank you

      1. Kevin, I need to rebuild my 67 OHC Sprint motor. Where can i find some info on how to rebuild it. I spun a cam bearing and the motor only has 68 K on it. I have read that they starve for oil getting to the cam and will spin a bearing on cold starts ( Do you have any Ideals on how to prevent this? ).

    4. hi, if you are still looking I have a ’68 ohc 6 motor may still run been out of car for awhile, I am in Oregon.

    5. Yes i have a 1967 OHC out of 1967 Fire bird Sprint rebuild able My email is chrissharon6 [at] msn [dot] com Thank you!

      1. Chris,

        I edited your email address to make it slightly less machine-readable — if you really want me to put it back the way it was, I will, but I take no responsibility for the spam-bots of the world!

    6. I Have A 1966 OHC Sprint Motor Complete nelsontolman [at] gmail [dot] com

      1. do you still have the sprint motor?

  16. It’s a damn shame that GM is such a bullheaded company when it comes to innovation.

  17. My first car was a Pontiac LeMans bought from my grandfather. It had the OHC six 2-barrel. I enjoyed the car for a year and then sold it to my parents. They had to rebuild the top end twice and finally junked it at 67,000 miles. The cam design was definitely flawed. Interesting to read all the knowledgeable comments about this engine.

  18. I worked, as a mechanic, at a Pontiac dealer and was excited when these cars stated coming in to be sold. They drove well and were economical. A few months later the only excitement was trying to keep them from eating their overhead cams. I could not believe that GM would release such junk.

  19. hi, i have 66 tempest custom still has the original engine ZD CODE that came factory in it with the optional four speed, it has 98.000 miles on it, at 80.000 miles had to put cam assembly on the engine, but she run’s just fine, and the only rust spot’s are at rear glass and above back bumper, floor’s solid, and i have rare 67 firbird ohc 6 sprint that came factory with transistorized ignition, the amp box mount above the heater, and it has the factory wiring, do you have something like this, tell me about it thank’s k.t.

  20. Can anyone confirm an attempt to extend the Pontiac OHC engine lifespan in Australia powering Holdens that soon fell apart once it was revealed to be close in power to Holden’s own V8 during that period?

    A pity it never lived on particularly in Australia along similar lines to the Australian versions of the Ford Straight-6 that eventually became the Ford Barra engine (topped with 320-420 hp 4.0 Turbo variants).

    1. I’ve never heard anything about that, although it does sound reasonably plausible. (I assume such a thing would not have been the Pontiac OHC six per se, but rather a similar OHC conversion of the existing Holden six, so as to preserve as much of the original tooling as possible.) There’s certainly a lot of precedent for that kind of thing. Of course, given how much GM-Holden probably spent tooling for the locally built V-8, I can see how they would ultimately have decided not to also go forward with an extensive revamp of the existing six, especially if it produced similar power.

  21. Loved your article on the OHC6.
    I’m still driving my 1967 LeMans, 2-door hardtop. Tahiti blue, OHC6,1-bbl Rochester carb, with the 2-speed power glide transmission.
    I bought her new in December, 1966, in Austin, TX. I drive it monthly with more than 178.000 on her. She’s 100% original with the same hub caps, gas cap, car keys, interior, etc.
    I overhauled the engine in 1979. The timing belt, with 142,000 miles on it, actually looked good. She still has the same cam and lifters.
    The main reason I still have this car is it’s beautiful design, at any angle, as well as such an easy driver.
    I just wanted to talk about Becky Blue (her name) since she’s at the New Braunfels Classic Car Restoration shop for a complete redo. It’ll be her 50th birthday coming due soon.

  22. I have always liked these Pontiac OHC sixes. I never owned one, but I did come close to obtaining a very old and beaten up 67 Lemans Sprint back in the 80s.

    These engines are very cleverly designed, and I still do not understand how they are more expensive to make that the corresponding Chevy stove bolt 6.

    For instance, the block is very simple: There is no machining for a cam, oil pump, lifter bores and lifter galleries, fuel pump, and a distributor.

    The oil pump, distributor, and fuel pump are mounted on a die cast aluminum assembly (somewhat analogous to the die cast front ends on Cadillac and Buick V8s). All of this was driven by an auxiliary shaft that was, in turn, driven by a pulley that was also used as the cam belt tensioner. This whole assembly moved up and down on a pad, machined on the lower right side of the block and was held to the block by four bolts working in slots in the die cast assembly. The whole assembly could be moved up and down against the block to achieve the proper cam belt tension. It was prevented from tilting out of alignment by a slot milled into the pad on the block and corresponding key in the assembly. Like the four mounting slots, inlet and output oil galleries in the block matched with slotted passages in the assembly.

    It seems to me that casting and machining a die cast part is less expensive than performing similar operations to make cast iron parts.

    There is more expense in making and setting up gears to drive the cam (as in the Chevy 6) than in making pulleys and a timing belt — this is even cheaper than making sprockets and a silent chain, as some other 6s used.

    The cam is held in another die casting, again, easier to machine than a cam in a cast iron pushrod block.

    I see this engine as being very adaptable to all sorts of uses, from a heavy duty truck engine (longer strokes could more easily be accommodated in a higher block that used the same tooling as the car block) and head design would be practically unlimited, with later aluminum technology, a cross flow head, and even a DOHC head. Performance, in other words, could be easily manipulated more cheaply than in the normal pushrod design.

    Unfortunately, Detroit’s lack of attention to engineering a reliable design was capitalized on by companies like Toyota and Honda, who found cheaper ways to make better parts and, much to their customers’ delight, didn’t expect their customers to do their trouble shooting for them.

    A word about the “Y Block” design of the block (and Y Blocks, as well!). Deep skirted blocks, so despised by the Cfhevy-Synchophant car rags, was a design used by GM, as well, such as the Small Block and Nail Head Buicks, in Chrysler’s B and RB V8s, and AMC’s old 287/327 V8s, besides Ford’s Y Block, Lincoln Y Block, FE, MEL, and SD truck motors.

    The purpose of the deep skirt is not to provide a means of using cross bolted main caps to increase the strength of the main caps, as those aforementioned car rag writers would have us believe.

    First of all, the purpose of cross bolted mains wasn’t to reinforce the main caps. It was to keep the main caps from “walking” on their seats and consequently allowing the mains to spin. This was a problem when slamming a two-ton stock car into a high speed corner at nearly 200 mph and then letting off of the throttle. The forces in the block are tremendous in this case, and anchoring the main caps was the problem. Ford FEs and Mopar 426 Hemis accomplished this by tying the main caps to the deep skirt with cross bolts.

    Pontiac, back in the early 60s, accomplished the same thing by using four bolt main caps on their skirtless V8 blocks in the early 60s — something Chevy later copied to solve similar problems.

    Furthermore, in a V8, it can be argued that the “Y Block” deep skirt does directly support the crankshaft partially, as it is clear (contrary to the silly arguments made by the most famous car rag) that in a V8 engine, the crank isn’t being pushed out the oil pan opening, it is being pushed at a 45* angle to perpendicular. This, however, is immaterial in an inline six.

    A famous inline six made by GM that used the deep skirted “Y Block” was the old Detroit Diesel, such as the common 6-71. The deep skirt is used to strengthen the engine longitudinally, which is why this design is quite common in many engines today. Regarding the Pontiac OHC 6, it would give the engine the durability needed in its high performance garb to push relatively heavy intermediates and pony cars around with surprising performance.

    Regarding the question posed by one of the posters in this thread, the Sprint engine differed from the base six, not only in having higher compression and a Rochester 4v Quadrajet, but in having a more radical cam and different, stronger rods. The block also has room to accept the long-stroke Chevy 292 truck inline six crankshaft.

    John Z DeLorean had admirable skill as an engineer, and this Pontiac engine is part of his legacy, along with other automotive designs you have related to us on this sight. It’s a shame that his business ethics didn’t match his skill, but the Pontiac OHC 6 is a design I’ll always admire.

  23. Have you ever heard of, or do you have any information about, an over head cam engine based on the Corvair horizontally opposed six cylinder engine? This engine was proposed for the GM Astro I show car in the mid 1960’s. The over head cams, one on each cylinder head, were belt driven, similar to the Pontiac’s OHC 6. This engine would have been in development around the time of the development of the Pontiac engine.

    1. The Astro I is mentioned briefly in the Corvair article and I think in the Opel GT story as well. Detailed information about its engine is surprisingly sparse. As far as I could gather, the show car didn’t actually have a running engine (not atypical for concept cars) and it’s not clear if there was a running version of the engine; it does not appear to have been a serious production prospect. It was notionally based on the existing Corvair engine, but taken out a bit in bore (which probably would have meant new cylinder barrels) for a displacement of 176 cubic inches. I have no information on the belt drive.

      1. Aaron, thanks for the info. I had an occasion to sit (or rather, repose, because of its laid back seating position) in the Astro I, but it was almost 4 decades ago, and although I knew of the significance of the car at the time, I didn’t memorize all details about it. I did notice it had sloppy spot welds in the engine compartment. The car did not run in our presence, so I can’t verify if whatever engine was in it was runnable. I understand that it now has a common 140HP (four Rochester H carbs) engine, mainly because somebody got tired of pushing it all over the place. I’m working with someone who is working with someone who insists there are six or seven operational Cammer engine prototypes in the wild (outside of GM), and he insists that he absolutely must have one. As you indicate, there is very sparse information about this engine. Someone claims to have the blueprints for this engine, but I’ll bet he has the blueprints for the experimental Rochester fuel injection Corvair engine. I have seen those, as well as a box of parts (but not assembled on an engine). I was hoping you might have had some insight or leads as to a direction of information about the Cammer engine, but you are reinforcing the concept that there is simply nothing out there to be had. I thank you for your info and response.

        1. If there were any operating prototypes, I’ve never heard of any — which doesn’t mean they don’t exist, necessarily. It’s certainly conceivable that Chevrolet engineering (or the corporate Engineering Staff) toyed with the idea of rigging up an OHC Corvair engine, but whether it got beyond paper plans and mockups, I don’t know. (The divisions in those days had “Advanced” engineering budgets for R&D projects not necessarily intended for production.) By the time the Astro I was built, the likelihood that Chevrolet would have seriously considered a more expensive high-performance version of the Corvair engine was pretty remote.

  24. Who has blueprints on the experimental cross-flow DOHC Pontiac-6? Those could be 3-D’d via sintered metallic powders & triple-lazers in a metal-substrate 3-D replicator. The greatest cost would be the alumno-titanium sintered powders. Is there a Pontiac Museum where a example may lie? A portible scanner could obtain enough info to replicate a DOHC alloy-head, and I would expect the patents have long expired.

  25. I got to own a 69 Firebird Sprint in the late 70’s early 80’s. Swapped 3 speed manual to M 4 speed and changed rear gears, not sure of #’s. Not the best off the line but it was sweet from 15 to 110. One of the funnest highway cars I have owned. Had to sell do to way to many tickets but I still smile thinking of that sweet ride.

  26. I owned a 1966 Tempest Sprint option, 3spd, 3.55, standard steering, brakes, etc. Went like crazy on the highway. I put 69,000 miles on it with no problems whatsoever. Drag raced it quite a bit and used nothing but Kendall GT-1 racing oil. I then purchased a 1968 Tempest Sprint with the same set-up, plus 15/1 steering ratio, heavy duty rear axle and traction-lock differential. It was a 250 cube and was a much better engine for off the line. I managed a record run with it at 15.29 at 86 miles per hour. With a fours speed and 3.90’s I could have easily got down into upper 14’s. Put 68,000 miles on it and also had no problem with the engine.

  27. Well get this… Mac McKeller was my cousins husband… he was a wonderful person to know and ride with in those new GTO take home cars… yep at 17 I had the pleasure of riding with him every night in a new car for a week while I visited with my relatives… God bless Mac and the rest of my family.

  28. Enjoyed reading all the responses here.I bought my first new car in July of 68, a Lemans Sprint optioned 3 speed, metalflake Verdoro green with y paunchet white interrior.First week I owned it , it developed an severe oil leak at the external oil pump housing – apparently not sealed correctly at the factory.I never had another problem with the car – drove it daily for 7 years and put 105, 000 mileson it.w What a really nice and fun car to own A totally reliable car and a lot fun to drive. I will own anot one some day.

  29. I have ridden more than a few miles in Pontiac OHC 6 powered cars. One was a Tempest with the base engine and automatic transmission. The other was a Firebird with the 215hp version with 4spd. The Tempest acted almost like a comparable Chevelle with 6 and auto, but in the upper rpm ranges a little peppier. The Firebird on the other hand sounded like a 6 but went like a V8. One night while speed shifting my friend left the rear end in pieces over a 150ft stretch of road which forced us walk 7 miles in the dark starting a 12:30am. Never heard of anyone else blowing a rear end with a six cylinder engine.

    In my opinion GM really screwed themselves royal by letting this engine die. It worked fairly well and most of the teething problems had been worked out by the time they let it die. When they needed newer and different engines due to gas crisis and other events they could have used this as a blueprint for a 4 cylinder OHC engine and refined it for use in the larger downsized cars without having to reinvent the wheel. The original Pontiac Tempest with a 4 cyl engine had the engine created by loping off one bank of the V8 engine Instead they drunkenly lurched from one disastrous engine to another and in the process with all the other missteps destroyed the worlds largest and most profitable car company. One engine alone wouldn’t saved GM but it would have greatly helped as not to have to reinvent the wheel.

  30. Loco Mikado
    August 24, 2016 at 7:30 pm

    One night while speed shifting my friend left the rear end in pieces over a 150ft stretch of road which forced us walk 7 miles in the dark starting a 12:30am. Never heard of anyone else blowing a rear end with a six cylinder engine.

    WELL…we scattered the AMC 15 rear end with a stroker 4.9 based on that OHV engine…still running about in millions and millions of Jeeps! Cured it by installing the Mustang 8.8.

    The sixes are, as Clifford Engineering’s Logo says: “6=8”

  31. Aaron, What you said;

    ” direct inspiration for Pontiac’s OHC engines was the contemporary Mercedes big six, a 183 cu. in. (2,996 cc) engine found in the Mercedes 300 sedans and coupes and, in somewhat more highly tuned form, the 300SL sports cars. With its iron block and single overhead camshaft, the Mercedes engine was not as exotic as the twin-cam engines from Jaguar and Alfa Romeo, but it had an impressive competition pedigree and offered a fair compromise between power, fuel economy, and complexity. It became the conceptual starting point for Pontiac’s design work.”

    The engine that comes even closer to the Mercedes is all of the L- series Nissan engines. L1300-L2000 4 cyl and the L2400- L2600 and L2800 six cylinder. We even use the same special valve adjusting tool for both engines!

  32. I have 3 Pontiac overhead cam motors, 1-spirit,250ci. (no carb), 1- 250 ci. with 2 speed trans complete, 1-230 ci. complete given to a college by Pontiac. willing to sell

    1. Are the engines still available? Where are they located?

    2. do you still have any of the Pontiac 6cyl motors for sale ?

  33. Our second new car after we were married was a 1966 Tempest wagon with the OHC six and standard transmission. I really enjoyed that car and there was just something nice about the one piece chrome plated shift lever! But the oil rings failed after 44,000 miles and oil was spraying out of the breather-filler all over the engine compartment. Rather than spend money on an out-of-warranty engine rebuild, I traded it for 1968 Chevy BelAir wagon. Memories!

  34. I bought a ’68 Firebird Sprint OHC 4 barrel new in 1968. It was a disaster. It *drank* oil through the valve guide seals. When it got down to 400 miles/qt (making it essentially a 2-stroke) the dealer would replace the valve guide seals. I did this 4 times under the warranty, and then got rid of the car.

    Excellent idea, terrible execution.

  35. Currently working on restoring a 68 FB Sprint with OHC six. I need some help with steps to pull the motor to replace all of the gaskets and seals as a result of an oil leak. Any help would be great as the last time I pulled the motor was in 1983 and I completely forgot what I did.

    Love this car an can’t wait to get it on the road again

  36. I bought a new ’66 Tempest Sprint, 3-speed after driving a co-workers base mode Tempest. To my everlasting regret I traded in a ’57 Chevy 2-dooe wagon with a built 283. (I worked in an automotive machine shop at the time and the Chevy was built for the ’56 Corvette I owned before acquiring a wife and child)

    The Sprint was fun and ran with the Mustangs of the time but fuel mileage was awful, although we normally didn’t worry about it back them.

    A friend bought what must have been a one-of-a-kind, special-ordered ’66 Chevy wagon with a 427 with full synchro 3-speed column shifter. It was insanely fast and the ultimate sleeper. GTO Pontiacs were its favorite food. I followed him from Phoenix to Durango CO once for a camping trip. He was loaded with camping gear, a wife and two Newfoundland dogs. I had a wife, infant kid and a suitcase. In the mountains I had a tough time keeping up with him and when we filled up, he got better mileage than I did. He probably weighed nearly twice as much as I, had twice the engine displacement and essentially the same carb.

    Memory fails to recall the exact engine problem that caused me to dispose of the car; a valve problem of some sort.

  37. Great article, learned everything about my (former) ’68 Sprint I wanted to and much more! If only I could get her back, sigh.

  38. Given what Ford of Australia did with the Straight-6 / Barra engines, GM missed an opportunity to improve on the engine by having an updated OHC layout filter down to the related Chevrolet Straight-6 (plus 153 4-cylinder) while spawning more potent Twin-Cam variants to replace the Pontiac OHC-6.

    1. They certainly did. At the time, GM corporate saw the OHC six as an unnecessarily expensive elaboration of an economy engine nobody really wanted anyway, but the picture would have looked quite a bit different five years later!

      A lot of the divisions played with OHC and DOHC concepts during this period, although it appears most of them were conceived as ultra-performance engines of a kind that wasn’t necessarily compatible with early emissions controls (at least with carburetors). However, even when that was addressed through electronic injection and feedback response systems, GM remained weirdly resistant to offering engines of that kind for a surprisingly long time. Low-revving pushrod V-8s and big sixes matched to automatic transmission seemed more their comfort zone.

      1. OHC mainstream cars didn’t really catch on in Europe until the 1970’s.
        The BMC E series engine in Austin Maxi’s and allegro’s, Fords into sohc offered in 1.6 and 2.0 liter sizes in Cortina’s and Capri’s joined the GM Vauxhall in the market all around 1970, Renault an Fiat also had OHC engines available. But many cars soldiered on with old fashioned ohv engines into the 1980’s and even beyond in a few cases.
        Most push rod engines could keep up with ohc engines for power and economy for everyday cars, it wasn’t until the European emissions regulations came int force in the 1990’s that manufacturers were essentially forced to adopt an ohc, and later, dohc layouts with the extra costs involved to meet the new requirements. One offshoot of this is modern engines with proper maintenance will outlast the older engines by a massive margin. Quarter million mile engines are far from uncommon, back in the day 100k miles was a fair life.


      2. Strange GM were reluctant to properly develop a long running ubiquitous engine, especially from the 3rd generation onwards. The same could be said of Chrysler as well with the Slant-6 despite them actually looking as properly developing the Slant-6.

        Given what the likes of Austin did with their copy of the 2nd generation Straight-6 (plus distantly related downsized engines), it could be argued GM actually had an almost perfect engine in the Straight-6 from which to develop and spawn related engines in a myriad of ways at relatively little cost.

        1. Well, yes and no. The big Chevrolet six was a fairly bulky, heavy engine to begin with and the Pontiac OHC version was more so. Even with the OHC, the 250 was not an especially free-revving engine, nor was it very economical by the standards of the ’70s (although for panicky buyers circa 1974, it would probably have seemed pretty good). The born-again Buick V-6 was lighter, a good deal more compact, and more easily adaptable to transverse FWD applications.

          1. The Striaght-6 as well as the related 4-cylinder would obviously be restricted to RWD models even with OHC/DOHC.

            That said GM could develop downscaled 4/6-cylinder versions of the Chevrolet 4/6-cylinder engines (or downscaled even further), roughly envisioned as being essentially a GM equivalent of the BMC B-Series (plus O/M/T-Series or Nissan J engine) without the involvement of Harry Weslake.

            Agree the Buick V6 is more adaptable to transverse FWD applications, yet a pity the closest GM ever got to a 60-degree V6 for passenger cars prior to the 1979 60-degree X V6 was a theoretical 60-degree V6 derived from the shelved 1960s Cadillac V12 prototype.

          2. Scaling down an engine is not a trivial matter, though, and is not necessarily desirable in a number of respects. There are three frequent results: a modest reduction in the weight or dimensions of an existing engine that doesn’t really justify the expense (e.g., the version of the BMC C engine used in the MGC and Austin 3-Litre); a lighter but weaker version of an existing design (e.g., the Pontiac “301”); or else creating a miniature version of an old engine that can’t share much if any of its progenitor’s tooling.

            The issue for companies the size of GM and Ford was always tooling, which is almost always the answer to the question, “Why didn’t they just reuse the design for X?” Designing engines or cylinder heads wasn’t a big deal for GM — they had engineers doing that all the time. It always came down to, “Where are we going to build this in the quantities we need and how much is that going to cost to set up?”

          3. The C-Series was actually completely unrelated to the B-Series because it was a pre-merger Morris design, with possible roots to the post-war SV Morris Six MS and OHC Wolseley 6/80.

            A 2-litre 6-cylinder version of the 1.2 4-cylinder Austin A40 engine (which formed the basis of the B-Series) was considered, with the intention to use as many common parts as possible to keep manufacturing costs as low as was consistent with reliability and servicing costs of the units. However it was not pursued due to the Austin 16 hp / Austin A70 being powered by a 2.2 4-cylinder, which was derived from Austin’s copy of the 2nd generation Chevrolet Straight-6 known as the Austin “D-Series” (making it a sort of 2nd gen-based 153 4-cylinder that spawned dieselized variants in taxis and powered the original Big Austin-Healey).

            Though a UK developed 6-cylinder B-Series never happened. The Australians later developed a 80-84 hp 2.4 6-cylinder B-Series known as the Blue Streak engine, while the Japanese built a 109 hp 2.0 6-cylinder B-Series copy called Nissan J engine.

            Interestingly during development of the MGC it was established the 2.4 Blue Streak 6-cylinder B-Series was not only significantly lighter and more compact compared to the Morris developed C-Series, but also capable of putting out 115 hp up to a maximum of 128 hp on the dyno.

            Could see GM initially developing a downscaled 6-cylinder at the lower-end of the North American market (followed by a 4-cylinder) possibly in place of the Chevrolet 153 4-cylinder, with Envoy models and even Opel (pre-CiH) utilizing both 4/6-cylinder engines. Such engines could have also evolved along similar lines to the B-OHC prototype and O/M/T-Series petrols as well as the Perkins and L/G-Series diesels with a very long production life.

          4. I wasn’t implying that the C-Series six was related to the B engine; my point was that it illustrates the practical limitations of trying to scale down an existing design while preserving the tooling.

            Again, there’s a clear temptation with these things to look at in engineering terms (or performance engineering terms) what are predominantly manufacturing problems. The primary reason GM or, to Roger’s point, Ford of England/Ford of Europe clung to old designs was that it was the path of least resistance from a production standpoint, not that they weren’t able to come up with better designs. For instance, GM’s North American divisions were not building any Opel engines (other than the handful of 327s Chevrolet built for Opel for the Diplomat 5,4) and were not equipped to do so. Therefore, using Opel engines would have meant either buying them from Germany or extensively reengineering the design for North American manufacturing and setting up a completely new line, at which point there was little incentive to use the existing design rather than something homegrown. It had very little to do with the superiority of the design.

            Also, I have to underscore again that until the late seventies and early eighties, it was very rarely a matter of “GM” developing something and more a question of whether an individual automotive division considered something worthwhile enough to put some resources into developing AND was able to convince corporate management to fund it. There was not a single unified engineering arm (or even North American engineering arm) doling out engine designs and deciding what the corporation as a whole might need. It was very different from Ford, Chrysler, or most European or Japanese manufacturers in that respect.

          5. Given the C-Series likely roots, an earlier 1.5 4-cylinder version was developed via the SV Morris Oxford MO and Wolseley 4/50 (with a 1.1 OHC was developed though not produced), additionally 4-cylinder OHV versions were developed though not pursued in 1750cc and 2-litre forms for the mk2 Morris Oxford and MGB (with some alleging the prototype engines were comparable to the Volvo B18 / B20 units).

            Had the merger with Austin never happened, came about later or under more equal circumstances (where Morris was not the weaker partner by investing like Austin did beforehand), it is likely a downscaled “A-Series” equivalent would have been developed to replace their own pre-war SV / OHV engines (that were essentially copies of the Ford Sidevalve engine). The post-war Morris Minor was originally intended to be powered by the 918cc Wolseley Eight OHV and would have received a 960-1000cc version had the merger not happened, with Morris engineers claiming it was better then the A-Series that replaced it.

            While understanding where you are coming from with each GM marque / subdivision having their own engineering arm and relative autonomy, the point is using downscaled engines derived from the Chevy Straight-6 / Pontiac OHC-6 (and related 153 4-cylinder would have negated the need for importing Opel engines and placed GM in a better position by the time the 1970s fuel crises hit.

            They would have not have to use Isuzu engines nor potentially even the Vega or Iron Duke engines at the lower-end of the range, as all could have been adequately taken over by a range of small 4-cylinder petrol and diesel engines (with distant scope for a 5-cylinder variant). The small 6-cylinder likely being pensioned off to South America and markets due to GM adopting the Buick V6 and other V6 engines.

          6. Here’s the thing: Chevrolet only offered the 153 four in the U.S. very grudgingly, and I don’t think production was ever very great. It was one of those things that was useful to have in the catalog, but that dealers didn’t want to order except maybe to have a bottom-of-the-barrel price leader for newspaper ads (“Prices as low as …”), and that sold in tiny numbers. Under those circumstances, having it be a derivative of the Nova six, sharing a lot of off-the-shelf parts, made sense. It was a minimal-investment option, and any significant variations from the engine on which it was based would have defeated the purpose.

            Had there been greater utilization of it, that picture would have started to change. Producing several different engines on the same line requires less capital investment, but it can really tie up production. At some point, it forces a decision on whether to kill the less-popular/less-profitable option or set up a second production line.

            If Chevrolet had decided they really needed a small four (which by sixties standards would have meant “2.0 to 2.5 liters”) in sufficient numbers to justify setting up a unique line, there would have been no particular advantage to maintaining the architecture of the 153/230 engines and various reasons why it wouldn’t have been desirable — too much weight and too much bulk for the sort of applications in which it would have been useful. And indeed that’s sort of what happened with the Vega 2300 engine, although that wasn’t conceived by Chevrolet. Chevrolet could undoubtedly have come up with something better, or at least less troublesome, but the old 153/230/250 family architecture would not have been either terribly useful in terms of addressing the logistical questions or in terms of performance.

            Broader use of the OHC version of the 215/230/250 engine — not scaled down, just a tidied-up version of the Pontiac six — would have made sense in the ’70s, but as a more economical alternative to low-end V-8s in X-body, A-body, and low-end B-body cars, not as a substitute for a decent, modern four or small six for cars like the Vega or the H-body compacts.

          7. The 153 was fitted to South African versions of the Vauxhall Viva HC called the Chevrolet Firenza including a 2-litre version (and opens up the possibility the engine could easily fit into similarly sized T-Car Chevette).

            Which makes one wonder if the 153 engine could have been fitted into larger Victor FB / FC / FD models, slotting both the Chevy II / Nova and Corvair either as an entry-level Chevrolet (if built in the US) via some early form of TASC or as more unique Envoy models.

            Agree with broader use of a properly developed Pontiac OHC-6 though would include smaller 181, 194 and 215 variants as well as equivalent Pontiac OHC-4 engines (particularly in 2-litre OHC-4 form), with the Australians embracing such an engine in place of the old Holden Six and later updating it to feature DOHCs.

  39. Must have been 7th or 8th grade when I first came into contact with an older kid who had a beautiful 66or 67 Le Mans Sprint that could outrun V-8’s. I have been a fan ever since but have not owned one. It seems these engines would be unusual replacements for cars that originally had Chevy 230’s and 250’s. Sad that many were tossed and replaced by V-8’s. I would like to replace my Impala’s 250 with an OHC-6 Sprint or even a base one. I have owned a number of the Chevy sixes, an Opel GT, a slant six Volare, 3.8 Transport, and two of the Vortec sixes in my GMC Envoys. I guess I am a “six” guy! (Only 2 V8’s in my lifetime, 283 sbc and an Olds 350) This was a fascinating string of comments and replies, thank you.

  40. Aaron, rereading your fine article again, may I observe that, while your description of the OHC design states that inertial factors make it generally superior to the pushrod OHV design, there’s another factor to take into account: especially in 50s to 70s Detroit wedge combustion chamber configurations, the pushrods form a “picket fence” through which the ports must pass, or, at least in the Detroit V8 crossflow head configuration, the intake ports must pass. This also forced constrains on the size and configuration of ports, which related to port flow and power production potential.

    Perhaps the best solution to this problem was Ford’s use of the “tunnel port”, which ran the intake port directly at the valve with the intake valve’s pushrod running through a tube passing through the port. While this resulted in a nice power increase for Ford FE 427 NASCAR motors, for some reason it was a failure for Trans-Am 302s, and Ford went to the “Cleveland” style splayed valve Boss 302 head design for that engine. Pontiac, somewhat later, whet to the tunnel port design for its Ram Air V engine.

    My point here is not that pushrod layouts absolutely prevented optimum port designs, but that in Detroit 6 and V8 engine designs with wedge combustion chambers, where the valves were in line across the head, they posed a limitation in head port flows. In Chevy and Mopar wedge V8s, two intake ports were squeezed side by side through this “picket fence”, where Ford attempted to lay ports out evenly, mandating longer runners to the end cylinders and resultant distribution challenges.

    1. That’s true, and has been a challenge with pushrod engines pretty much as long as OHV engines have existed. (I confess I’m not familiar with the porting arrangement on GM’s LS1 and later modern OHV V-8s, although I imagine if nothing else, they have the advantage of sophisticated computer modeling that would have made engine designers of the sixties weep with envy.) That said, it’s hard to make any absolute statements insofar as it is possible to design a pushrod head so that the pushrods don’t present any great impediment to porting, although there are costs for that in other areas, as Chrysler’s old FirePower and 426 Hemi engines demonstrated. The reduction in inertia is something that applies even if the porting isn’t necessarily that different.

      An interesting case study in this regard is Toyota’s 1.6-liter 2T engine of the seventies. The standard 2T was pushrod, but it had hemispherical combustion chambers, so its breathing was already quite good. The 2T-G had a Yamaha-designed DOHC head, also with hemispherical combustion chambers. In gross output, the dual-carb twin-cam engine had an advantage of 10 PS JIS or 12 hp SAE, or just about 10 percent, over the dual-carb pushrod 2T-B. The gross power peak was the same for both engines, but the 2T-G had a bit more torque and a higher (gross) torque peak, which makes me think the cam profile was about the same. Some of the difference was that the twin-cam engine had a higher compression ratio (0.3 or 0.4 points, due I think to a thinner head gasket), some was due to the 2T-G’s bigger valves, and some was the reduced inertia. I can’t quantify it a lot more than that, but it gives some idea of how these things stacked up in terms of output.

      1. Aaron, examination of the GM LS engines is somewhat interesting, since they remind me mostly of the Ford FE series. The ports are evenly distributed along the manifold face, and are tall and narrow, like an FE. GM has apparently abandoned trying to sneak paired ports through the pushrods. Your observation regarding computer analysis is interesting, given this choice and its divergence from past practice. Perhaps in the days of carburetion, Chevy and Pontiac engineers didn’t like the fuel distribution they got with an evenly spaced layout, but now, with dry intakes and injection, find it more suitable.

        Using splayed valves, as the Hemis (early, 2nd Gen, and modern) and Mopar polyspheres used, along with Ford 335 (Cleveland and 385(Lima and Boss), permitted a wider window of opportunity for porting. Big Block Chevys had splayed valves, but still stuck with paired, rather than evenly spaced ports, which allowed large ports but gave two “bad” ports and two “good” ports in each head. But wedge chambered heads with the valves in line, along with American 6s, had the picket fence issue.

        Your example of the Toyota engines isn’t familiar to me, but I’d think that splaying the valves in the pushrod hemi version would show pretty close performance, given the way that flow rate technology was applied at the time. Something a little closer to my knowledge would be the Ford FE SOHC and Mopar 2nd Gen Hemi — both were had configured combustion chambers, and both had similar intake flow rates in stock form.

        As I think about that OHC == pushrod example, it occurs to me that designers may have had more latitude with OHC designs when it came to using cams of larger base circle than pushrod engines. Larger cams allow a faster opening valves. The Ford SOHC, however, had rollers on the cam end of their rockers, which is a “cheating” way of getting around a small cam, like radiused lifters.

        Anyway, you are right: there are ways of getting around a “picket fence”, at the cost of other issues. The inline valve wedge heads of the 50s and 60s were retained (or adopted, in the case of Chrysler) because they offered something serviceable at lower cost, like the flatheads before.

        1. Regarding fuel distribution, the other consideration that I imagine was significant in the sixties was that most cylinder head designs had to be compatible with an assortment of different carburetion and injection setups. Of course, some engines were only offered (at least from the factory) in one specific configuration, but GM divisions were generally very keen on offering 2V, 4V, and even 6V or 8V versions of many of their engines, which likely entailed certain compromises in basic design. (The divisions did come up with exotic variations intended only for performance, like the Boss 429, but the applications for those were narrow and senior management was pretty frequently saying, “Look, boys, could you please develop some engines we can actually sell to Mom and Pop? Remember, we’re not in racing.”) Modern engines all have port injection, direct injection, or a combination of the two, so fuel distribution is now a very different picture.

          Another consideration may be that many if not most modern engines now have technologies like cam-phasing and variable-length intake runners. A port design that might be less than ideal where valve timing/duration/lift and intake runner length/shape/diameter are constants might work just fine where the latter parameters can be dynamically altered.

          Old JDM Toyota engines are an interesting study because there are a bewildering number of variations on the same basic engines. The T-system four, for instance, had low- and high-compression versions, several different carburetion options (supplemented by the late seventies with electronic injection), OHV and DOHC versions, and even for a while a lean-burn version using (under license) Honda CVCC technology. Many of these were offered side-by-side at different times, so, they’re a good reference point if you want to get a sense of how changing a given parameter affects engine output.

  41. Traditional Detroit engines were mildly tuned with low specific power, getting their output from cubic inches rather than RPMs. The high-revving capabilities of OHC would have been wasted on them.

    1. For most Detroit passenger car applications, that was definitely true. The exemplar in that regard was the contemporary Oldsmobile L66 Turnpike Cruiser engine, which was ruthlessly optimized for the 1,000-to-3,000-rpm regime. The fact that it was essentially breathing through a straw, even by the standards of sixties wedge-head pushrod engines, was a feature, not a bug; its design parameters didn’t call for more than two carburetor venturi, much less overhead cams. Of course, that’s a strategy that works better if you have more than 6.5 liters of displacement and no punitive displacement-based taxation rules!

  42. sir I have a 1969 ohc 250 4 barrel cast iron exhaust header and the 4 speed transmission. I would like to sale it do you know of any one who might be intrested

    1. I can’t help with buying or selling parts, sorry!

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