Pontiac 428 Specs

by James Jordan
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The Pontiac 428 cubic inch engine was used only from 1967-69. It was one of the largest engines Pontiac produced, but it was used more to power big cars such as the Bonneville, and not as much for performance cars such as the Firebird. Since that time it has been used as a performance engine in several cars by drag racers.


The Pontiac 428 engine was a bridge between two engines, which meant the 428 had a short lifespan. The engine remains popular with performance car enthusiasts, but in 1969 the factory only installed them in larger cars. Sometimes you could get a dealer to install one in a Firebird, and the engine was at times used in NASCAR racing. In 1967 the 421 engine was bored out to become a 428. The bore -- the width of the pistons -- changed, but the stroke, or the distance the piston travels, did not change. The iron used for the 428 block was stronger than what was used in the 421. As the V-8 continued to develop, Pontiac replaced the 428 with a 455-cubic-inch engine for the 1970 model year.

Engine Details

In 1967 the engine was used to power the 121-inch wheelbase Bonneville. This car was almost 19 feet long. The engine was a V-8 with overhead valves. It had a bore and stroke of 4.12 and 4 inches, respectively. The fuel and air mixture was compressed by a 10.5 to 1 ratio before ignition. The engine had five main bearings and hydraulic valve lifters. A four-barrel carburetor was standard. A three-speed automatic transmission was standard and a three-speed manual was an option. The engine used six quarts of oil and 17 quarts of coolant. The larger cars had 26 gallon gas tanks in 1967.


The 428 was rated with 260 horsepower at 4,600 rpm, and that could be boosted to 270 with some factory modifications. The engine had 472 foot-pounds of torque, or pulling power, at 3,200 rpm. By the 1969 model year, power had reached 290 horsepower. Also in 1969 one of the 428 engines reached 360 horsepower with smaller valves and a higher compression ratio. The compression ratio was 10 to 1 in this engine, 1.91 inch valves were used, along with a 1.66 inch exhaust. Normal valves were 2.11 inches and regular exhaust was 1.77 inches. Dual exhausts were used.

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