What Is the Difference Between a 350 Engine and a 400 Engine?by Moss Strohem
Introduced in the mid 1950s, the small block Chevy (SBC) used a standard V-8 engine block design that was physically smaller and lighter than the Chevy big block engines. They have been built in different displacements ranging from 262 to 400 cubic inches. Both the 350 and 400 cubic inch engines are SBCs.
SBC V-8 Design
The Chevrolet SBCs were configured in a 90 degree V, overhead valve (pushrod) design with cast iron blocks and block-housed camshafts. Cylinder heads were generally made of cast iron and used two valves per cylinder. External dimensions for all Gen I and II engines were the same. Different displacements were achieved by varying bore and stroke combinations.
350 CID SBC
The 350 engine used a 3.48 inch stroke, internally balanced crankshaft, 5.7 inch long connecting rods and had a cylinder bore diameter of 4 inches.
400 CID SBC
Initially designed as a high torque/low performance engine, the 400 used a 4.125 inch bore and a 3.75 inch stroke with 5.56 inch long connecting rods. The increased bore diameter required GM to alter the block internally with cylinder bores that did not allow for cooling passages between them. The crankshaft also had main journals that were 2.65 inches in diameter (as opposed to the 350s 2.45 main journals), and the crankshaft was externally balanced (on the harmonic balancer and flexplate).