What is the difference between a Pontiac 400 and a Pontiac 455?
The Pontiac 400 has a bore of 4.12 and a stroke of 3.75. The
Pontiac 455 has a bore of 4.15 and a stroke of 4.21. The 455
cylinder heads will have larger combustion chambers than the same
year 400 heads to achieve comperable compression ratios on the
larger engine. The blocks are physically the same size, but 455 has
larger main bearings than the 400. 455=3.25 400=3.00, so
crankshafts will not interchange.
Cams,heads,intakes,exhaust,connecting rods,push rods,rocker
arms...etc will all interchange.