The 400 Pontiac engine was a new evolution of the familiar Pontiac V-8 introduced in 1955 and an upgrade of the 389 built from 1959-66. In addition to an overbore from 4.06 to 4.12 inches, the updated Pontiac V-8 featured new freer-flowing cylinder heads with larger 2.11-inch intake and 1.77-inch exhaust valves, as well as revised ports and a new closed combustion-chamber design. The familiar Tri-Power induction system was replaced with a new single 4-barrel induction system. It used an intake manifold patterned after the 1963 421 SD NASCAR manifold and was topped with a Rochester Quadrajet carburetor. In order to keep insurance rates reasonable, Pontiac did not increase the top horsepower rating, keeping it at a conservative 360 HP.
