Cammer: The Pontiac OHC Six

TEMPEST SPRINT

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, but was rated at 165 gross horsepower (123 kW) compared to the Chevy’s 140 hp (104 kW). The OHC engine was not enough to make the Tempest a fast car — Car Life clocked a four-door Le Mans hardtop with automatic at 0-60 mph (0-97 km/h) in around 13 seconds — but it was stronger 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. It was rated at 207 gross horsepower (154 kW) and 228 lb-ft (308 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 — in January 1966, Motor Trend clocked a four-speed Tempest Sprint hardtop at 0-60 mph (0-97 km/h) in a tick over nine seconds with a top speed of 118 mph (190 km/h). 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 Tempest Custom convertible (with wheel covers from a ’62 Pontiac). (Photo © 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 Car and Driver‘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 a Popular Mechanics owner survey in 1966 found that even the base engine seldom exceeded 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 made more sense in the 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.

FIREBIRD SPRINT

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, with the Sprint package as one of four engine options.

1967 Pontiac Firebird Sprint rear
As with the Tempest/Le Mans Sprint, the 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 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 (324 N·m) of torque, most reviewers found the Firebird Sprint noticeably slower than the ’66 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 Man despite smaller dimensions. Car Life‘s well-equipped 1967 Firebird Sprint was actually 40 lb (18 kg) heavier than their ’66 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 40DCN 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 Quadra-Jet, 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; in May 1967, Motor Trend clocked an automatic Sprint from 0-60 mph (0-97 km/h) in around 12 seconds, running the quarter mile (402 meters) in the high 18-second range. (Photo © 2006 Robert Nichols; used with permission)

THE DECLINE AND FALL

Going from chief of Advanced 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. In his 1994 interview with High Performance Pontiac, DeLorean said ruefully that his tenure at Pontiac pushed senior management to crack down on divisional autonomy far more than they ever had before.

The OHC six eventually became another point of contention. DeLorean’s immediate superiors, GM group vice president Roger Kye and executive vice president Ed Cole (who became GM president in 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 its Chevrolet cousin. It also had higher warranty costs: While the timing belt was quite 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 the 1968 model year, Chevrolet stroked its 230 cu. in. (3,769 cc) six to 250 cu. in. (4,095 cc). Pontiac did the same, but the Chevrolet’s new counterweighted crank was apparently not compatible with the higher-revving “cammer.” Designing a new crankshaft and connecting rods presented no great technical challenge, but it further reduced the OHC six’s already limited commonality with the Chevy engine, making the Pontiac engine that much more expensive to build.

Cole and Kye found the costs of the OHC six hard to justify, particularly given its modest sales; more than three-fourths of buyers opted for the V8, which was cheaper to build. The tall OHC engine also posed some packaging problems: It would not fit in the engine bay of the second-generation Firebird without a prominent hood bulge. Cole finally ordered DeLorean to discontinue the cammer in favor of the cheaper Chevrolet engine. As with the Banshee, DeLorean fought to save the OHC engine, but it was to no avail.

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 at up to 230 hp (172 kW) with manual transmission. Sales were very low; we don’t have a precise figure, but it was probably well under 5,000 units. (Photo © 2006 Robert Nichols; used with permission)

In February 1969, DeLorean was promoted to run Chevrolet, replacing Pete Estes as general manager. His successor at Pontiac, Jim McDonald, was a production man, not an engineer, with little interest in either technical innovation or battling management. The OHC six was quietly dropped at the end of the 1969 model year. Development of the OHC V8s was canceled, as were a number of experimental versions of the six, including one with hemispherical combustion chambers. The focus of engineering development was shifting to emissions control and 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 thoroughly 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.

14 Comments

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  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.

  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. 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…

  8. 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

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