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Cammer: Pontiac's OHC Six




Written by Aaron Severson
Saturday, 24 April 2010 00:00



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 Fabulous 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 by 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 that 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 by 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, 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. It became the starting point for Pontiac's design work.

THE TIMING BELT

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, as well as 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, consumes little power, and requires no lubrication. Better still, it's considerably cheaper than either gears or chains.


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 internal damage. (Photo © 2006 Robert Nichols; used by 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, beginning with a 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 1.0 L (61 cu. in.) and eventually expanded to 1.7 liters (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 strong enough for a torquey big-bore six presented a bigger challenge. Furthermore, McKellar didn't consider the Glas engine's frequent belt changes acceptable; he wanted a belt that would last the useful life of the engine, with little to no maintenance.

Developing the belt itself was the biggest single challenge of the design process. Simple rubber belts were not strong enough or durable enough. Steel-reinforced belts had adequate strength, but tended to corrode. Stainless steel eliminated the corrosion, but was too expensive, and showed signs of fatigue at high mileage. The eventual solution, developed in partnership with Richard Case of Uniroyal, was a one-inch (25-mm), neoprene-impregnated fabric belt, reinforced with fiberglass. It was strong and durable, and testing showed minimal wear at high mileage. Unlike some later timing belts, it was not overly sensitive to dirt and oil, although Pontiac ultimately decided to keep it covered, protecting it from snow and road spray.

The rest of the engine was a study in compromise. The block was loosely based on that of Chevrolet's 1962-vintage OHV six, sharing its crankshaft and connecting rods, but the skirt was extended about 2.4 inches (60 mm) below the crank centerline, for greater rigidity. The oil pump, fuel pump, and distributor were driven by an accessory drive shaft mounted parallel to the crank. The heads used wedge-shaped combustion chambers with side-by-side valves, like Pontiac's V8s. To save weight, the camshaft was actually mounted in the aluminum valve cover, rather than in the head itself, and it had unusually wide lobes, in an effort to reduce wear. The valves, shared with Pontiac's V8s, were quite large: intake diameter was 1.92 inches (48.8 mm), exhaust was 1.60 inches (40.6 mm), the biggest the ports would accommodate.


The "cammer" had an iron block and heads, but the cam cover (where the camshaft is actually mounted) and the belt cover are aluminum. 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 by permission)

One of the bugbears of many early overhead cam engines was the need for periodic valve lash adjustment. That, too, was unacceptable; division policy required all fully warrantied engines to have hydraulic valve lifters, which prevented over-revving and needed no adjustment. Hydraulic lifters had never been seen as practical for OHC engines, but Pontiac engineers developed a clever solution. Although the camshaft was mounted almost directly above the valves, it actuated them through finger-type cam followers (essentially small rocker arms). The pivot point for each cam follower was a small hydraulic sphere, similar to a hydraulic lifter on a pushrod engine. The hydraulic sphere maintained a constant zero valve lash, without adding to the reciprocating mass of the valvegear. These hydraulic valve lash adjusters reduced mechanical noise, and they eliminated the need for routine valve adjustments.

Despite those novel features, the Pontiac engine was notably less racy than its European contemporaries. The basic version, with a single-throat carburetor, 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 be said for its more exotic British, German, and Italian rivals. It was not unlike Hollywood remakes of popular European films -- a similar concept, recast with familiar faces and a bigger effects budget.
OHC EIGHTS

Prototypes of the 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 6.9 L 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 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 Chevy Mk. 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 (6.4 L) engine, 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 dual overhead cams with four valves per cylinder, a cross-ram intake manifold, and sequential fuel injection. Although the DOHC V8 initially used chain-driven cams, it was later converted to a more robust version of the six's timing belt, with similar hydraulic valve-lash adjusters. Pontiac never released power figures for the DOHC engine, but it was probably well over 500 hp (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 OHC 421, with one belt-driven cam per bank and two valves per cylinder; with Tri-Power carburetion, it was capable of some 620 hp (462 kW). This was followed in 1965 by a SOHC 428 (7.0 L) V8, with a rear-mounted cam drive and three valves per cylinder.

McKellar showed off the experimental engines to Hot Rod editor Eric Dahlquist in 1968, but none of the 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 very powerful engines. A 500-horsepower (373-kW) SOHC V8 would have been a provocative gesture as far as Washington was concerned, and GM brass was in no mood for provocative gestures.
THE BANSHEE

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 John 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, it was a compact fastback coupe, looking something like a miniature Corvette Sting Ray. It 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.


There were two running Banshee prototypes (not counting earlier non-running mock-ups), 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. (5.4 L) V8, which probably would have been optional if the Banshee had made it to production. (Photo © 2009 EvThoMcC; used by permission)

GM management was unenthusiastic about the Banshee, preferring Pontiac to 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. DeLorean assigned Advanced Engineering chief Bill Collins to oversee the project, which proceeded with great secrecy.

In the summer of 1965, DeLorean was promoted to general manager of Pontiac. Seeing his opportunity, DeLorean had Bill Collins show off the two fully finished XP-833 prototypes to senior management. Collins made a thorough presentation, describing the Banshee's expected market position, tooling costs (a modest $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 it would help to bolster Pontiac's sporty image.

Unfortunately, GM chairman Jim Roche and president Frederic Donner were not interested. They thought the XP-833's lack of rear seats would limit its sales potential, and said it 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.
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 Chevy-derived 215 cu. in. (3.5 L) pushrod six as the standard engine of the 1966 Pontiac Tempest/Le Mans.

In its initial form, the OHC six displaced 230 cubic inches (3.8 L), the same as the pushrod six used by the Chevrolet Chevelle/Malibu, but it was rated at 165 gross horsepower (123 kW), compared to the Chevy's 140 (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 kph) in 13.3 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. They were particularly excited about the optional four-barrel version of the "cammer," which Pontiac advertised as an answer to exotic European engines.


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 by permission)

The four-barrel OHC engine had the same displacement as its more mundane sibling, but it 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. (4.6 L) engine, for instance, was rated at only 195 hp (145 kW).

The four-barrel engine was marketed as part of package called Sprint, which 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, it 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 kph) in 9.2 seconds, with a top speed of 118 mph (190 kph) -- and with less weight on the nose, it 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.


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 by 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 L 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, bringing it 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. (4.9 L) 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 something under 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.


The Sprint's greatest rival was not any competitor, but Pontiac's own 326 cu. in. (5.4 L) 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-horsepower (123-kW) OHC six was standard, with the Sprint package as one of four engine options.


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 less than 5,000 '67 Firebirds were Sprints. (Photo © 2006 Robert Nichols; used by 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 its 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 hope, a backslapping 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. Less 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, it 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.


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 kph) in 12.2 seconds, taking nearly 19 seconds to run the quarter mile (402 meters). (Photo © 2006 Robert Nichols; used by 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 production costs, including sharing some parts with the contemporary Chevy six, the OHC engine was still more expensive to build than its Chevy 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 corporate management.

For the 1968 model year, Chevrolet stroked its 230 cu. in. (3.8 L) six to 250 cu. in. (4.1 L). Pontiac did the same, only to find that Chevy's new counterweighted crank was 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 it 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 Chevy engine. As with the Banshee, DeLorean fought to save the OHC engine, but to no avail.


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 by 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, the tooling for the cammer was long gone by then, leading Pontiac to develop the thoroughly undistinguished 301 cu. in. (4.9 L) 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.

LEGACY

The next GM car with 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. (2.3 L) OHC engine for long. In 1978, the Vega four was replaced by the 151 cu. in. (2.5 L) 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. Unfortunately, many later timing belts were far less robust than Pontiac's was, and many 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 were slower to spread to other mass-market cars, although they began appearing on some luxury cars in the early seventies. They are now extremely common on OHC engines, in part because maintaining a constant valve lash helps to control exhaust emissions. (Having owned several cars that required valve adjustments every 15,000 miles (24,000 km), however, we consider hydraulic lash adjusters a tremendous convenience.)

It's unfortunate that the OHC six was something of a dead end for Pontiac. 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 many years afterward. Along with the turbocharged Oldsmobile Jetfire V8 of a few years earlier, it was one of the most sophisticated American engines of its era. It 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, but if DeLorean and McKellar had had their way, they 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 Hot Rod's Eric Dahlquist salivating.

Alas, it was not to be. Only one of the 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 what might have been.

[PMD1969]

[PMD1969]

[Formulabruce]

1964 >> OHC>>> Banshee Style....




The last "Breath" >Before the plug was pulled on the program, Pontiac built a few experimental versions with a special OHC Hemi cylinder head. They reportedly made 325 hp, though they never had a chance to call any engine bay their home.

Read more: http://www.highperformancepontiac.co...#ixzz1csaM5prT

[Jeff Hamlin]

[Jeff Hamlin]

[Jeff Hamlin]

[Jeff Hamlin]

[Jeff Hamlin]

[Jeff Hamlin]

[Jeff Hamlin]

[Formulabruce]

1968 250 "Cammer" with a 4-71 Blower



WEBBERS!!!

[Jeff Hamlin]

[MikeNoun]

The 67 PSFT Firebird, with the first "shaker" scoop.

[Jeff Hamlin]

[Jeff Hamlin]

[Jeff Hamlin]

PRE-PRODUCTION PIC. NOTE THE AFB CARB.
The 1966 OHC 6 Sprint was the first Pontiac production use of the all new Q-Jet.

[boater bill]

Jeff,
Do you have the July '67 Motor Trend Article for the PFST Sprint?
Could you scan and post it please. I can't find my copy I got of the article back in 86. Used the collegiate library article exchange program and Michigan State had it and sent a copy to me.

[Jeff Hamlin]