Pontiac V8 Engine History: 1955-1981
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.
The V-8 Reaches Production
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 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 valvetrain 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.
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.
The Super Duty Era
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 castiron 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.
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 Corporate Edict
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.
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.
Major 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.
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 Round-Port Era
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 highperformance 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 valvetrain 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.
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.
Living with Low Compression
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.
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 Era
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.
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.
Emissions and Economy
New federal emission standards shook the industry during the 1975 model year. Pontiac utilized a single exhaust catalyst and a compression ratio of just 7.6:1 to ensure total compliance. High-ratio rear axle gearing was used to keep engine speed relatively low, which lessened emissions and improved fuel economy. Performance suffered and the 455 was emasculated to just 200 hp. A change that affected all 350 and 400 engines was the introduction of the “lighter” block castings in mid 1975. Pontiac knew that high-revving engines had become a distant memory, so in an attempt to shed overall vehicle weight, material was removed from low stress areas of the block. The blocks are reliable for normal duty applications, but should not be used in any high-performance effort.
Another significant change occurred in mid 1976. Pontiac eliminated the common harmonic balancer on most 350 and 400-ci engines backed by an automatic transmission. A crankshaft hub was used in its place and it served as an accessory drive and contained a top dead center (TDC) timing mark.
The 455 was discontinued after 1976 and a high-performance 400 took its place in 1977. Rated at 200 hp, the new T/A 6.6 received a compression boost to 8:1 using 350-spec 6X cylinder heads, a unique camshaft, and specific carburetor and distributor settings.
With heavy emphasis placed on maximizing fuel economy, Pontiac developed a small-cube V-8 in a lightweight package to complement the downsized models it would introduce in the near future. The short-deck 301 was Pontiac’s answer to Chevy’s 305 and engineers had no intentions of it being a performance mill. The svelte block was filled with a crankshaft that had only one large counterweight at each end and cast connecting rods.
Revised camshaft timing and exhaust enhancements bumped the 400-ci T/A 6.6 to 220 hp for 1978, and durability issues arose with the lighter-weight 400 block. Pontiac revived a former 400 block casting specifically for 1978–1979 T/A 6.6 engines. These castings were as good as earlier units and can be identified by the “XX” cast into several locations on the block. Pontiac’s 350 was discontinued after the 1977 model year, and the last 400 blocks were cast on Thanksgiving weekend 1977 and stockpiled for use for the remainder of 1978. Several thousand were set aside for the 1979 Trans Am.
The End of an Era
The 301 was Pontiac’s only V-8 left in production by 1979. The T/A 6.6 was available for most of the model year, but once the supply of stockpiled 400s was exhausted, it signaled the end of the big Pontiac V-8.
A turbocharger was added to the 301 to give the 1980 Trans Am an injection of performance. With turbo boost limited to less than 10 pounds, the 301 was rated at around 200 hp in both 1980 and 1981. General Motors ceased Pontiac V-8 production in March 1981. It was the final chapter in a saga that started in 1955 and concluded after 14,624,886 engines were produced.
Pontiac always maintained a performance image and a great number of hobbyists competed regularly with their Pontiacs in various stock and modified classes.
Some of those who have successfully campaigned Pontiacs during the 1950s, 1960s, and 1970s include Arnie Beswick, Truman Fields, Jim Hand, John Angeles and Pete McCarthy, Art Peterson, Nunzi Romano, Milt Schornack, Mickey Thompson, Jess Tyree, Jim Wangers, and Arlen Vanke. These guys drove some of the quickest Pontiacs to ever make a pass down the drag strip in their day.
Resource Credit: pontiacdiy.com