According to information on the Mortec page, the small block 400 had a bore
of 4.125 and a stroke of 3.76. The big block 400 had a bore of 4.125 and a
stroke of 3.76. Both calculate to 402 and both were called 400 by Chevrolet.
I often wonder what was going on. This was just when cars had become subject
to California smog restrictions and more were soon to become effective. It
was also a few years before the major reductions of engine variations by GM.
It would have been VERY unlikely that two engine blocks would just happen to
work out to the exact same bore and stroke. The big block was a slight
increase from the 396 (only 30 thousandths larger). I always figured that
was some manufacturing convenience that came about when the block was
recored to handle the 4.250 bore of the 454, but now I'm beginning to
suspect it was for some other reason. It is just too much to accept that it
came out with the same exact bore and stroke as the new small block 400 all
by accident, and at the same time too.
In 1967 the GM engine line-up standardized on the 350 displacement. The
Chevy 327 got a new crank to become a 350. This was the first time a 'wierd'
bore or stroke dimension was used. (The 265 was 3.750 bore and 3.0 stroke.
The bore increased 1/8 inch to 3.875 for the 283. Then it increased another
1/8 to 4.000 and the stroke increased to 3 1/4 for the 327. It seems obvious
to me that the engineers picked a bore and a stroke and the displacement
came out to whatever it came out to be. Note the change with the 350 - bore
stayed the same as the 327 but the stroke increased from 3 1/4 to 3.48
inches - not 3.5 inches you would have expected. Seems obvious the GM front
office had decreed that the displacement should be exactly 350. Same year
Pontiac increased the 326 to 350, Olds came up with a 350 etc. Sure looks
like a pattern to me.
Same year the Pontiac 389 turned into a 400. Don't remember the Olds or
Buick - hope someone can contribute what they did. Interesting thing to me
is that the Chevy 396 did NOT change to 400. (Could it be because SS-396 was
too powerful a marketing tool to mess with?) But then 3 years later it
turned into a 402. When all the GM divisions - Pontiac, Olds, Buick went to
a 455, Chevy did the 454.
I'd love to read a book about the corporate planning and the Chevy vs GM
intrigue that must have been going on back then. There was talk of
government anti-trust action against GM back then (notice how the government
picks on the successful firms till they lose it) and the guess was that
Chevrolet would be broken off as a separate company leaving GM with BOP and
Cadillac. Could that have been behind some of the engine identity posturing?
Or was it about preparing for the engine/drivetrain simplification that
occurred in the 70's. Remember the law suits about Olds owners who sued
because their car came with a Chevy engine? And for a few years all the GM
adverts in the magazines came with fine print that said, "GM automobiles may
be equipped with engines from various GM divisions" or something like that
so they wouldn't get sued again. Maybe the plan all along was to have a 350,
a 400 and a 455 and phase out the different division's engines and just have
one of each. Kinda like there used to be a Hydra-Matic, a Dynaflow, a
PowerGlide, a TurboGlide and that changed to a Turbo-Hydra-Matic 350 and a
THM 400 that served all divisions?
Anyone else have any insight on this?
Gwyn Reedy
Brandon, Florida
mailto:mgr@mgrcorp.com
> -----Original Message-----
> From: owner-oletrucks@autox.team.net
> [mailto:owner-oletrucks@autox.team.net]On Behalf Of Kevin Lake
> Sent: Sunday, March 14, 1999 11:53 AM
> To: MarkNoakes@aol.com; oletrucks@autox.team.net
> Subject: Re: Re: [oletrucks] 366 V-8/big blocks
>
> Weren't all of the 400ci motors small-blocks? I have seen a 402ci. big
> block, but I thought all of the 400ci motors were small-blocks.
>
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