GM Engine Sizes (was Chevy engines)

Gwyn Reedy mgr at mgrcorp.com
Fri Nov 6 18:16:08 GMT 1998


Curtis writes...................

>  The 350 you have is a pontiac 350 (assuming it wasn't swapped
>out).  Its actual displacement was 354.  They called it the 350 because
>chevy had such good luck with their 350.


All this talk about GM engines leads me to postulate a theory about GM
engine size and ask if anyone really knows...

In the fifties and prior each division had its own frame and suspension, own
transmission (although some shared Hydra-matic) and own engines. In 65 the
Turbo Hydramatic came out and over several years became the GM-wide
transmission.

My theory is that GM was planning from the early sixties to simplify their
engine families.
That would explain why in 1967 all the divisions standardized on 350 and 400
cu in instead of what they had prior. Chevy went from 327 to 350. Stroke on
the 350 is 3.48 inches. Always prior the stroke had been a fractional number
(3 inches or 3 and one quarter). Rodders had been making 352 cu in small
blocks for a number of years ( 4 inch bore and 3 1/2 stroke) so you'd have
expected Chevy to go for a 352. I figure it had to be corporate policy
telling the divisions to all come up with 350 so that in subsequent years
one of the 350 blocks could become the GM standard. That is what they
eventually did, sort of.

Interesting part to me is how Chevy did and did not play along with this.
They did the 350, but kept the 396 unchanged instead of making it a 400.
Few years later they increased it to 402 and badged it a 400. I have a 72
pickup with a 402 that says 400 on the fender. In the manual the various
engines are listed. The 307 is a 307, the 350 is a 350, the 454 is a 454,
but the 402 is a 400. Also note that then all the other divisions went from
427 or 428 to 455, Chevy instead went to 454.

Sounds like politics within GM to me. Or am I reading too much into it? I
presume Chevy kept the 396 because they had vehicles (SS396) based on that
number. That doesn't explain the 454 vs 455 though.

Comments?

Gwyn Reedy
Brandon, FL




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