With all the furor surrounding Ford and Chevy'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 that promised V8 power and six-cylinder economy.

This week, we look at the short life of Pontiac's "Cammer."


(Photo © 2006 Robert Nichols; used with permission)

JOHN DELOREAN AT PONTIAC

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, was a skilled machinist who had worked in Ford's Detroit foundry. 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, he 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 considering other job offers.

A contact at GM, Oliver Kelley (the corporate research engineer who helped develop Hydra-Matic and Dynaflow), arranged a meeting between DeLorean and new Pontiac general manager Semon E. "Bunkie" Knudsen. DeLorean was initially put off by Pontiac's stodgy reputation and GM's top-heavy corporate culture, but he was impressed by Knudsen and his plans to reinvent Pontiac. Knudsen offered to make DeLorean the head of a new advanced-engineering section, with a starting salary of around $14,000, a handsome sum in the mid-fifties. On September 1, 1956, DeLorean joined Pontiac as chief of Advanced Engineering, reporting to new chief engineer E.M. (Pete) Estes, whom Knudsen had recently recruited from Oldsmobile.

DeLorean's initial brief at Pontiac was to develop new engineering concepts that might eventually find their way into production cars. Much like at Packard, DeLorean was given a free hand to explore novel and sometimes radical ideas. One of his first major projects was a rear transaxle with an unusual flexible driveshaft, later used for the 1961 Pontiac Tempest. Another, less-successful concept was a six-cylinder engine employing a curious hybrid of air- and water-cooling. Unlike the Tempest's flexible driveshaft, it proved unworkable, and was eventually abandoned.


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. (3.2 L) slant-four engine, essentially Pontiac's 389 cu. in. (6.4 L) V8, shorn of one cylinder bank. Buick's 215 cu. in. (3.5 L) V8 was optional in 1961-1962, but rarely ordered; less than 5% of buyers selected it. (Photo © 2009 Norm Stephens; used with permission)

By 1961, DeLorean had moved on to a new project: an advanced six-cylinder engine with a single belt-driven overhead camshaft.

SIDEBAR: CAMSHAFTS, OVERHEAD AND OTHERWISE

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.


The camshaft of 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, geared to turn at one-half 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 2. 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.


Diagram of a typical pushrod/rocker-arm layout of an overhead-valve engine. (Illustration © 2007 Ian Brockhoff; used under a Creative Commons Attribution ShareAlike 3.0 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, instead of 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 make them more difficult to "package." Second, overhead-cam engines (and particularly engines with dual overhead cams) are usually somewhat heavier than pushrod engines, with a higher center of gravity. Third, an OHC V6, V8, or V12 requires two camshafts -- four with dual overhead cams -- where a pushrod engine can get by with one. Finally, 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, or gear or shaft drive to run the camshafts, any of which adds complexity and cost.

Those trade-offs made OHC engines were 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 less 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 four and the Willys/Kaiser Tornado engine, an OHC conversion of the old 230 cu. in. (3.8 L) Willys flathead six. The Tornado six was short-lived in America -- Kaiser Jeep dropped it after 1965 -- but it was used by Kaiser's Argentine subsidiary, IKA, well into the seventies.


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 they minimize the reciprocating weight of the valvegear, and they 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.

THINKING SIX

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 dropped its venerable flathead six at the end of the 1954 model year, and didn't offer another 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. It presented an attractive opportunity to explore new ideas.

Both John DeLorean and motor engineer Malcolm McKellar were intrigued with OHC engines, both for their practical advantages (see 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.


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 the later V12 was SOHC. This engine had an enviable pedigree: in competition trim, it won the 24 Hours of Le Mans five times.

In a 1994 interview with High Performance Pontiac magazine, John DeLorean recalled the direct inspiration for Pontiac's OHC engines was the contemporary Mercedes big six. With a single overhead camshaft, it was not as exotic as the twin-cam engines from Jaguar and Alfa-Romeo, but it offered a fair compromise between power, fuel economy, and complexity. The Mercedes engine became the conceptual starting point for Pontiac's design work.

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Comments (10)

• 2010-04-25 17:08:46 | Norm  - Cammer: Pontiac's OHC Six

  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.

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• 2010-05-01 14:40:45 | Administrator

  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.)

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• 2010-04-26 11:52:38 | res

  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.

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• 2010-04-26 12:49:22 | Administrator

  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).

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• 2010-05-01 12:42:38 | Staxman  - Hmm . . .

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

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• 2010-05-01 14:38:30 | Administrator

  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.)

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• 2011-04-07 14:58:10 | Marc

  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.

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• 2011-05-04 06:30:00 | Andrew Buc  - Malcolm McKellar has just died

  http://wheels.blogs.nytimes.com/2011/05/03/malcolm-mckellar-pioneer-of-the-pontiac-overhead-cam-engine/?hpw

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• 2011-07-26 12:57:09 | barry  - OHC timing marks, or pully position

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

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• 2012-01-05 19:07:52 | Rick

  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

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