Introduction of the Pontiac V-8

• Pontiac had been with GM since the 1920s, and had been working on a new overhead valve V-8 design for nearly ten years before the engine actually debuted in 1955. The Pontiac V-8 may never have made it to production at all if the Chevrolet small block -- which borrowed much of the experimental Pontiac's architecture -- hadn't gone into production in 1954.
  
  

Pontiac Evolution

• The first Pontiacs had what we know today as a reverse-flow cooling system, but engineers dropped the system so they could move the generator and power steering pump to accommodate a lower hood line. Pontiac doesn't divide their V-8s into "big" and "small" blocks like Chevrolet. All Pontiac engines other than the heavy-duty 421, 428 and 455 cubic inch engines used a block with a 3.00-inch main journal. The larger engines used a 3.25-inch main journal, but were otherwise almost identical. The original Pontiac 400 was a bored-out version of the popular 389, which it replaced in 1967 to remain in production for a full 12 years.
  
  

Pontiac 401 Specs

• The Pontiac 401 actually displaced 400.4 cubic inches, but Pontiac enthusiasts often chose to round the number up instead of down to distinguish the engine from Chevrolet's "Turbo-Jet 400" big block, which itself actually displaced 402 cubic inches. The Pontiac 401 used an "over square" design, meaning that its bore (4.125 inches) was longer than its stroke (3.75 inches). Power ratings ranged from about 255 horsepower and 397 foot-pounds of torque to 325 horsepower and 440 foot-pounds in 1967. Power ratings remained consistent until 1972, with the most powerful being the 370-horsepower 1969 through 1970 Ram Air IV. Power dropped precipitously during the 1970s to about 170 net horsepower (includes all accessories and exhaust). By older gross horsepower standards, late '70's engines probably generated about 210 to 235 horsepower.
  
  

The Other 400

• While the original 400 remained in production until 1979, Pontiac dropped it from use in the Trans Am, Grand Prix and Bonneville in 1977. To facilitate cross-division platform sharing, GM replaced it with the Oldsmobile 403, but chose to retain the "400" nomenclature for marketing reasons. The Olds motor was massively "over square," with a short 3.385-inch stroke and the second widest bore ever used on a domestic V-8 (4.351 inches). The 403's 185 horsepower and 320 foot-pounds of torque aren't Earth-shattering by today's standards, but the engine was far lighter than the old Pontiac and its "over square" design meant that it had great high-rpm potential for such a large engine.