The Chevy 400 was produced for just 10 years and became Chevy/GM’s go-to engine model for full-sized pickups, the GMC Jimmy/Chevy Blazer, and even in mid-sized A-Body and B-Body sedans.
The Chevy 400 features a 4.125 in bore and was rated for around 250 hp.
Unlike other Chevy small block engines, the 400 included siamesed cylinders to alleviate hot-spots in the engine’s cooling system.
4-bolt 400s were produced from 1970-1972. After that, Chevy/GM converted the 400 to 2-bolt mounting.