Pontiac 400 Specsby James Jordan
Pontiac introduced the 400 cubic inch V-8 in performance oriented cars in 1967, and continued to make the engine available through 1979. The 400 is a bored out 389, which had been in use for a few years. Pontiac typically changed engine sizes by modifying the internal workings instead of the outward size, so many of the engines appear identical, though they may have vastly different specifications.
The Pontiac 400 engine was used as a high performance engine in sports cars, and it was used in large cars as a workhorse type engine, strong on power, though not as speedy as the higher performance engines. This was accomplished to a large extent by the use of carburetors. A two-barrel producing less horsepower and higher torque was developed. A four-barrel carburetor allowed the engine to have more air, and that resulted in more horsepower for speed. Valve angles and diameters were also adjusted according to the way the engine would be used. Higher performance engines had valve intakes at 2.11 inches and exhaust valves at 1.77 inches. The "lower" performance engines had 1.96-inch intake valves and 1.66 exhausts.
In the 1968 Pontiac GTO, the 400 cubic-inch V-8 was tuned to deliver 360 horsepower and 445 foot-pounds of torque, or pulling power. The engine had a bore and stroke, or size of the cylinder and distance it travels, at 4.125 and 3.75 inches. A four-barrel carburetor produced a fuel and air mixture that was compressed to a 10.75:1 ratio. The engine had hydraulic lifters and five main bearings. The 1968 Pontiac Executive Series, with the same 400 cubic-inch engine with a two-barrel carburetor, had 290 horsepower and 428 foot-pounds of torque. The bore and stroke was the same as that of the GTO. By 1975, with more emission control standards, the horsepower was down to 185 in the full-sized Pontiac sedan, and the torque was 310 foot-pounds by that time. Compression ratio had gone down to 7.6:1.
When introduced in 1967, the 400 engine was available on most Pontiacs, from the GTO that had a 115-inch wheelbase, to the Firebird with its 108-inch wheelbase, as well as the Bonneville, Catalina and Executive on either a 121- or 124-inch wheelbase. After 1970 it was no longer offered on the Bonneville as it was replaced with the 455. The LeMans began using the engine in the early 70s. In the Mid 70s it was used in the Grand Prix.
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