In the 1960s and 1970s, Chevrolet and Pontiac both offered a pushrod V8 engine with an advertised displacement of 400 cubic inches. Considering that both carmakers are (were?) sub-brands of parent company General Motors, one might assume that these two engines share a similar architecture or might even be the same, but that's hardly the case. The Chevy has a bore and stroke of 4.125 inches and 3.75 inches, respectively. Meanwhile, the Pontiac has a 4.12-inch bore and 3.75-inch stroke. While that aspect of the two motors is admittedly nearly identical, that's where the similarities end.
Chevy's 400 cubic inch V8 debuted for the 1970 model year and ran through 1980. It was significantly based on the small-block V8 that Chevy launched in 1955, which powered more cars than any other engine, ever. Chevy's 400 was also one of the largest small-block V8 engines until the 427-cubic-inch LS7 came out in 2006.
The Chevrolet 400 was designed to provide extra torque in vehicles like large sedans, trucks, and early SUVs like the 1988 K5 Blazer. While it could be modified for performance, Chevy's 400 never made much horsepower in factory form. Fortunately, the same isn't true for Pontiac's 400, which powered many of the brand's iconic muscle cars and pony cars.
Steve Lagreca/Shutterstock
Considered by many gearheads to be the first muscle car and perhaps even considered one of the best muscle cars ever, Pontiac's GTO roared into showrooms in 1964 with a brand-specific 389 cubic inch V8 under the hood. It's that exact engine which would get bored out slightly to measure 400 cubic inches for the 1967 model year. To be sure, Pontiac installed the 400 in some boring grocery-getter sedans and wagons, but it also had a rambunctious Ram Air IV version that represented the apex of power for this engine.
In 1969, the Ram Air IV made 345 horsepower in the Firebird and 370 horsepower in the larger GTO. This was an era when manufacturers used fantastical gross horsepower ratings — measured without exhaust or parasitic drag from accessories like an alternator — that couldn't be replicated in the real world. By contrast, some muscle car fans claim that the Pontiac 400 was actually rated at less than its true potential.
In 1970, Pontiac's don't-call-it-a-big-block 455-cubic-inch V8 dethroned the Ram Air 400 as the top-dog engine option in performance machines like the GTO and Trans-Am, noted for the bird that Pontiac put on its hood that looked like a screaming chicken. Pontiac dropped the 455 after 1976, once again making the 400 the engine to covet in "Smokey and the Bandit"-era Trans-Ams (promoted as a sophisticated "6.6 Litre" displacement) until it too was discontinued in 1979. By comparison, perhaps the best thing that can be said for Chevrolet's 400-cubic-inch small-block is that a 400 crankshaft in a 350 block makes the desirable 383 stroker, a hot rodding favorite that Chevy sells in crate engine form to this day.
