- 1965-1967 "Early" 400s used a slightly oversquare 4.000 in (101.6 mm) bore and 3.975 in (101.0 mm) stroke for an overall displacement of 399.6 cubic inches (6,549 cc). All the pre-1968 engines used a forged steel crankshaft.
- 1968 and 1969 400s shared the Olds big-block standard 4.25 in (108 mm) stroke with the 455 but used a very undersquare3.87 in (98 mm) bore to comply with GM's displacement restrictions in the A-body cars while also reducing tooling costs. Displacement is very close to the earlier engine, at 399.9 cubic inches (6,554 cc). This "later" 400 is considered less desirable by many enthusiasts, because of the power band characteristics induced by this exceedingly undersquare format, although the actual change in power was due to the mild 250/264 duration cam used in this engine (previous 400s used a 278/282 cam)[citation needed] and the fact that the crankshafts were now made of less durable high nodular iron material.
"Early 400s" used the same forged steel crankshaft as the 425, while "later 400s" used the same cast iron crankshaft of the 455, with rare exceptions; some 1968 and later Olds 400/455s were produced with forged steel crankshafts. These rare cranks can be readily spotted by the "J" shaped notch in the OD of the rear flange; cast iron cranks have a "C" shaped notch. All 1965-1969 Olds 400s were painted bronze.
