GM Engine Sizes (was Chevy engines)

Greg Hermann bearbvd at sni.net
Fri Nov 6 23:20:11 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

Part of it was a corporate edict to the effect that no cubes over 400 would
be allowed in an intermediate size (B-body) vehicle. Another edict was no
more than 4 carb holes on such vehicles. I think 350 may have been another
size edict, for another vehicle class.  On the really big cube motors,
there were no edicts as to cubes vs. body type, so they varied. 427's, of
course were all due to the early '60's NASCAR 7 liter max. rule. Do not
remember whether NHRA did a 7 liter max for a while too, or not.  I think
that 428 was a common GM size due to an edict about making sure that the
big motors did not go racing. All due to political concern over hipo stuff.
Later, concern over anti-trust action, far more than economics (gummint
make 'em split off Chevy??), led to cross division parts use and assembly
division separate from the car divisions. GMC trucks used to use Poncho
V-8's in late '50's, too. GMC also had an inline 6 that not a lot of folks
remember, a fuzz over 300 CID, which was a serious torque monster, and
extremely durable. Did very well in C-gas and D-dragster type NHRA stuff.
Not a lot of people realize that the (later) GMC 307 CID V-6 truck motor
was a sawed off 409. Or that they built a 351 CID V-6 and (a times 2) 702
CID V-12 (both truck motors). O, P & Cad used the old 4 speed hydramatic
from its inception in the late '40's till the end. Buick used the two speed
Dyna-Flow/Powerglide with a 5 element converter from late forties till
whenever. EXCEPT the Hydramatic div. plant burned to the ground, I think in
late '54, so you can find some thing like Power Glide '55 Ponchos that were
built factory stock on an emergency basis. I have even seen early '50's
Cads with a power steering pump which said "Vickers" right on the pump.

TH 400 came out in '63 or so ???? (Believe Caddy was last to change over
from a four speed, this may be when they did it.) Chevy used the Power
glide till later ('65??) when the TH350 came out. (They finally figured out
how to build a three speed cheap and junky enough to suit Chevy!! :-)

Aren't dictators funny critters???!

Regards, Greg





More information about the Diy_efi mailing list