What is the difference in the gm engine 400 and 455?
If you mean the difference between the Pontiac 400 and
455....the differences are the bore size, the crank stroke length,
and the main bearing journals. All are bigger on the 455. However,
there is also a small block Chevy 400....which has nothing the same
as the other two. The Pontiac 400 has a bore of 4.12, stroke 3.75
and 3" main journals. The 455 has a bore of 4.151, stroke of 4.21,
and 3.25" main journals.