The Boss 302 engine is a racing small-block V8 from Ford Motor Company. It was a hybrid of two small-block Ford V8s - It used the block of the small Ford Windsor engine and the heads of the larger Ford Cleveland engine. It was created for the SCCA's Trans-Am road racing series, and was fitted to the Boss 302 Mustang.
The high nickel content block has a thicker deck, cylinder walls and beefy 4-bolt main caps. It is easily identified by screw in freeze plugs on the side of the block, pent roof valve covers, very wide heads and a very wide intake manifold. The connecting rods are heavy, high strength steel forgings made for high rpm use. The crankshaft is a cross drilled high strength steel forging. The cam and lifters are high lift solid mechanical units.
Boss 302 engine as fitted to the Mustang
The unique, wide, large port Cleveland style 4V heads with poly angle, semi-hemi style valve placement are what give the Boss 302 its unique high power capabilities. Early units were typically characterized by very large intake and exhaust valves sitting in a small quench style combustion chamber. Huge intake ports made certain that the engine only "woke up" above 4000 rpm. At racing speed the engine's performance was quite remarkable especially in the upper rpm ranges.