In 1954, General Motors leaned heavily on Chevrolet and Pontiac to develop V-8 engines for the 1955 model year and provided them with all available resources to ensure success.
Pontiac settled on a 3.75-inch bore and 3.25-inch stroke to produce a 287-ci package. Pontiac management urged that the design allow for future displacement increases, which eventually permitted the basic combination to displace 455-ci in a matter of years.
Pontiac’s 287 block featured five 2.5-inch-diameter main journals that support a forged-steel crankshaft. The left-hand cylinder bank was offset rearward. This allowed the distributor to be mounted on the right side of the block, exposing its driven gear to upward thrust, eliminating the need for a machined thrust surface within the block.
The cylinder heads incorporated 1.78-inch intake and 1.5-inch-diameter exhaust valves. A reverse-flow cooling system directed coolant toward the cylinder heads before the lower end of the engine in an attempt to extend exhaust valve life.
The block’s lifter galley was fed with a relatively high volume of oil to accommodate hydraulic valve lifters to provide quiet, consistent, and maintenance-free valve train operation. The rocker system, consisting of a stamped-steel rocker arm pivoting on a single stud, was one that many other manufacturers adopted for their V-8s in later years.
Engines featuring a compression ratio of 7.4:1 were rated at 173 hp. A machined (decked) cylinder head was utilized to boost compression ratio to 8:1, and increased horsepower to 180. A 200-hp version was introduced in mid 1955 when a 4-barrel carburetor was made available.
Engine displacement grew to 316.6 for 1956, and horsepower increased to 205 for the 2-barrel and 227 for the 4-barrel. Optional dual exhaust added about 10 hp to either engine. Pontiac created its first extra-horsepower package in mid 1956. With more compression, dual 4-barrel carburetors, and a special camshaft, the combination boosted horsepower to 285.
Semon “Bunkie” Knudsen was appointed as Pontiac’s general manager toward the end of the 1956 model year. With the promotion came instructions to drastically change the division’s image beginning with 1957. In addition to revisions he made to body styling, Knudsen hired Pete Estes who was part of Oldsmobile’s very successful high performance V-8 program—as chief engineer, and a young John Z. DeLorean as assistant chief engineer.
Even though General Motors agreed to adhere to the Automobile Manufacturer’s Association (AMA) 1957 recommendation, which stated that manufacturers should refrain from encouraging any type of speed or acceleration-related contests, Pontiac increased V-8 displacement to 347. A trio of 2-barrel carburetors, heralded as “Tri-Power,” was made optional, increasing horsepower to 290. The top performer designated for NASCAR-type competition still utilized dual 4-barrel carburetors and cranked out 317 hp.
Displacement increased to 370 for 1958 and horsepower increased accordingly. The engine grew yet again in 1959 to 389 ci, and it remained at this size for 1960. That year also initiated Pontiac’s illustrious “Super Duty” era.
A complete over-the-counter parts package with the sole intent of producing a competition-only 389 was released in 1960. It employed the same four-bolt block used in Tri-Power applications, but the Super Duty package filled it with a forged-steel crankshaft and connecting rods. High-flow cylinder heads produced 10.5:1 compression and a solid-lifter camshaft with 1.65:1-ratio rocker arms controlled valve action. High-flow cast iron exhaust manifolds (with separate collectors that could be uncapped) were offered, and a single 4-barrel or Tri-Power intake manifold was also used.
Actual output of the Super Duty 389 wasn’t published, but certain racing series required that manufacturers provide a horsepower rating, so Pontiac arbitrarily rated the 4-barrel engine at 348 hp while the Tri-Power was rated at 363. The combination was quite successful as Pontiacs went on to win 7 of the 44 NASCAR races in the 1960 season, and Pontiac ad-man Jim Wangers piloted a 1960 Ventura to the NHRA National championship.
The 389 was carried over into the 1961 model year and the Super Duty package went on. Intake manifold choices were limited to a single 4-barrel or Tri-Power. While both were previously cast iron, for 1961 they were cast in lighter weight aluminum. Either engine was rated at 368 hp.
The Super Duty combination proved to be lethal. Pontiac was dominating drag strips around the country and it captured 30 of 52 NASCAR race wins during the 1961 season. The 421-ci V-8 debuted in Pontiac’s parts books toward the end of the 1961 model year and was a direct response to Chevy’s 409, Ford’s 406, and Mopar’s 413. It’s generally accepted that none were factory installed.
The Super Duty 421 was comprised of a new 4.09-inch bore block with four-bolt main caps, a forged-steel 4-inch stroke crank, forged-steel connecting rods, and forged-aluminum pistons. It utilized the same cylinder heads as the 389, which pushed compression to 11.0:1, a cast aluminum dual 4-barrel intake manifold, and a solid-lifter camshaft. Rated at 373 hp, the package made Pontiac an even greater threat on the racetrack.
If success is measured by competitive wins, Pontiac was the manufacturer to beat in 1962. The possibilities seemed limitless with the persuasive John DeLorean having been promoted to chief engineer the previous year.
Until that point, certain forms of racing simply required that a given component have a factory part number for it to be legal for competition. That translated into a flood of aftermarket components arbitrarily hung with manufacturer part numbers with the sole intent of satisfying these governing bodies. It didn’t take long for the National Hot Rod Association (NHRA) to catch on and revise its ruling for certain stock classes. Such components not only needed to have a manufacturer’s part number, but they had to be factory-installed too.
Pontiac responded with the announcement of a series of “special purpose” factory-built vehicles. This simply meant that Pontiac installed both the SD-389 and SD-421 into vehicles on its assembly line. The SD-389 was limited to a single 4-barrel while the SD-421 used dual 4-barrels. Both engines received the McKellar number-10 camshaft, which was much like a solid-lifter version of the hydraulic number-041 of later years. The SD-389 was rated at 385 hp, while the SD-421 was at 405.
The 1963 Super Duty 421 received new pistons, which raised the compression a full point over the previous year to 12:1. The single 4-barrel version was rated at 390 hp, while the dual 4-barrel unit was rated at 405 hp as in 1962, even with the increased compression ratio. A separate dual 4-barrel engine with 13:1 compression was also available in 1963, and it was (under)rated at 410 hp.
Pontiac released a revised cylinder head for its Super Duty engines early in 1963. Boasting improved exhaust flow, it had no official effect on output rating.
The bottom seemingly fell out of the performance car market at General Motors in January 1963. GM Chairman Frederic Donner issued a memo to all divisions reaffirming its position on the AMA agreement against racing.
This meant that manufacturers couldn’t openly sponsor race programs, and that experimental components had to be covertly supplied to racers. Vehicles were produced for a few months even after the edict was imposed, however, as evident with the “Swiss Cheese” Catalina’s, but General Motors was serious and its Divisions were forced to comply. Pontiac utilized the experience gained from the Super Duty program to create its newest performance street engine, the 421 High Output (421 H.O.).
The 421 H.O. was essentially a detuned SD-421. It consisted of a four-bolt block and number-716 cylinder heads, which were similar to the Super Duty units but contained an exhaust crossover to improve cold-weather operation. An aggressive hydraulic-lifter camshaft was employed, and it utilized Tri-Power induction and high-flow cast-iron exhaust manifolds. It was rated at 370 hp.
A new performance Pontiac entered the market in 1964 and it changed the industry forever. The new “GTO” was built on the intermediate Tempest platform. The 421 H.O. seemed to be a natural fit for the new GTO, but GM’s power-toweight- ratio standards limited maximum engine size to just 389, so Pontiac simply created a 348-hp 389 using components familiar to the 421 H.O.
John DeLorean was promoted from the position of Chief Engineer to General Manager in 1965. His rebellious attitude allowed him to push many of his technological visions through to production.
Pontiac engines had typically been painted a shade of green or blue up to this point. DeLorean wanted buyers to find the vehicle’s engine as attractive as its exterior, so in 1966 the Pontiac V-8 was painted a light metallic-blue, and a chrome-plated air cleaner and valve covers were added in performance applications.
Though the same engine packages were carried over, the Tri-Power’s end carburetors were made larger for improved airflow, and that boosted horsepower of engines so equipped. A dealer-installed “Ram Air” package was made available for the GTO late in the 1965 model year. The hood scoop insert was cut open, allowing the engine to ingest cooler outside air, conceivably producing more power. The Ram Air package became a Pontiac trademark for years to follow. It never increased the advertised output rating, but it certainly offered a performance benefit.
V-8 Design Changes
Pontiac was forced to abandon its signature Tri-Power induction system in 1967 when General Motors banned multiple carburetion on all vehicles except the Corvette. Rochester’s new Quadrajet 4-barrel was Pontiac’s choice for its performance applications.
To be sure the new 4-barrel engines performed at least as well as the previous 360-hp Tri-Power engine, airflow was improved by reducing piston-to-valve angle from 20 to 14 degrees, and increasing valve diameters from 1.92/1.66 inches to 2.11/1.77 (intake/exhaust, respectively) in performance applications. Streamlined exhaust manifolds were used to improve flow, and the block bore diameter was increased .030 inch, which boosted displacement to 400 ci.
In addition to those changes, Pontiac completely redesigned the intake manifold using the 1960s Super Duty 4-barrel manifold as a template. The dual-plane design featured long, smoothly contoured runners to produce maximum torque at low speed. Though there was large push to cast the manifold in aluminum to save weight, cast iron was ultimately used to quell reliability concerns and maximize cold-weather operating characteristics.
The 421 was also slightly affected for 1967. As the full-size offerings grew in size, they required even more horsepower to maintain performance. Pontiac increased the 421’s bore to 4.12 inches, which produced 426.5 ci when combined with the 4-inch-stroke crank. To maintain its own identity in a market filled with the 426 Hemi and 427 Chevy, Pontiac’s was billed as a “428.”
The Ram Air 400 available in the GTO and new Firebird was very much the same for 1968, and it came to be known as “Ram Air I” when a new Ram Air engine was brought to market in May 1968. The Ram Air II (R/A II) was rushed through the development process so Pontiac could give its customers a high-winding V-8. It borrowed technology from a new high performance engine that Pontiac was developing for 1969, which contained some very unique pieces aimed at reaching its intended 6,000-rpm limit.
The R/A II featured all-new cylinder heads with redesigned round exhaust ports. The port work improved exhaust air-flow by about 10 percent over a comparable D-port, and the outlet shape was intended to make fitting tubular headers easier for racers. The valve train was comprised of specific heavy-duty components, and the new number-041 hydraulic-lifter cam was teamed with 1.5:1 rockers to produce .470 inch of valve lift. The combination was rated at 340 hp for the Firebird and 366 for the GTO.
Two new performance engines were introduced for the 1969 Firebird and GTO, and both carried over into 1970 with minimal changes. Rated at 335 hp for the Firebird and 366 in the GTO, the 400 H.O., or Ram Air III (R/A III) as it was later known, utilized D-port cylinder heads and high-flow exhaust manifolds. Pontiac’s top engine option in 1969 and 1970 was its Ram Air IV (R/A IV), which had a solid 6,000-rpm operating limit. The intake-port roof of the round-port R/A IV cylinder head was raised 1/8 inch and the intake port volume was increased from 153 to 180 cc, which allowed it to operate at its intended limit.
The high-flow R/A IV cylinder heads were complemented by a new castaluminum 4-barrel intake manifold with enlarged runners and separate cast-iron heat crossover. The 041 camshaft teamed with 1.65:1 ratio rocker arms produced a gross valve lift of .520 inch the most ever used in any production Pontiac engine. The mill was rated at 345 hp for the Firebird and 370 hp for the GTO. Increased displacement was required to motivate GM’s full-size cars, which continued getting larger year after year. Pontiac’s 428 grew to 455 in 1970 by increasing bore size .030 inch and replacing the 4-inch-stroke crank with a 4.21-inch unit. The 455 H.O. was comparable to the previous year’s 428 H.O. and availability was limited to larger models and the GTO. The R/A III and R/A IV continued as Pontiac’s top engine options in the GTO and Firebird model lines.
To regulate emissions, General Motors imposed a compression-ratio cap of 8.5:1 for the 1971 model year. That signaled the end for the R/A IV. Pontiac knew that increasing displacement meant similar horsepower could be attained at a lower RPM. By combining R/A IV–type components with the 455, Pontiac created the new 455 H.O.
Adhering to the imposed compression ratio limit, the 455 H.O. featured modified round-port R/A IV cylinder heads, a cast-aluminum intake manifold, and high-flow exhaust manifolds. The 068 camshaft was chosen to maximize low-end torque, and specific hydraulic lifters were used to effectively limit engine speed to no more than about 5,500 rpm, quelling warranty claims from overextended operation. The new engine carried a gross rating of 335 hp, and 305 hp at the new “net” rating, which more closely represented engine output when installed in a car. It remained Pontiac’s top engine option for 1972.
In response to more stringent exhaust emission standards, exhaust gas recirculation (EGR) was introduced for 1973. It consisted of a valve mounted on the intake manifold that allowed metered amounts of inert exhaust gas to re-enter the combustion chamber. The biggest news that year, however, was Pontiac’s newest performance engine, the Super Duty 455.
The Second Super Duty
The SD-455 was a max-performance effort designed to operate at 6,000 rpm. Additional material was added to the SD-455 block to increase overall rigidity, and it contained a provision for dry sump oiling at the rear. A nodular iron crankshaft with deep-rolled fillets was employed. It was retained by four-bolt main bearing caps. Specific forged-aluminum pistons were complemented by beautiful forged-steel connecting rods.
The SD-455 cylinder heads’ intake port volume was increased to 186 cc to allow for 6,000-rpm operation, and the exhaust ports were precisely modified to maximize flow. The intake port was so wide near the entrance that its sidewall actually broke into the adjacent pushrod guide passage, and a thin-wall steel sleeve was pressed in to seal it. Specific valve springs and high-quality 2.11/1.77-inch valves were also used.
A new 800-cfm Quadrajet and a specific cast-iron intake manifold with enlarged runners were used with the SD-455. A 041-spec hydraulic camshaft was used throughout development and testing, lending to its 310-hp rating, but when it finally reached production in May 1973, a 744-spec cam was used to ward off emissions concerns, and the engine was subsequently rerated at 290 hp. Availability was limited to the Firebird model line. Only 295 SD-powered Firebirds were produced in 1973, and all were the 290 hp variety. An additional 1,000 Super Duty Firebirds were produced in 1974.