Chevy engines

[Curtis Mittong]

someone writes...................

I have a 1976 Pontiac Firebird with a 350 CI engine, is this engine GM
or Chevy?
How can  you tell the difference between the two engines, I was told
Pontiac used Chevy engines in some Firebirds but when or in what models
I dont know.
Is there also any obvious differences between the 350, 400 & 450! ?.


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The pontiac engine was its own engine starting in 1955 and was its own
engine until 1981.  Rumor had it that some Chevy engines filtered over by
1980 in the big Parissienne.  This includes 301, 326, 350, 389, 400, 421,
428, and 455.  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.  I tell pontiac engines by looking
at the heads.  They are very distinct.  Chevy heads have the exhaust face of
the head about 90 degrees from the stroke, so the manifolds or headers go
out, then curve down.  Pontiac heads are cast so that the exhaust mating
face kinda points downward.  Pont heads have a casting number on the center
exhaust port boss.  Yours would probably have one of the following: 6X, 4X,
5C, or 7K3.  Also, most chevy engines with mechanical fuel pumps had them on
the passenger side, while pontiacs are on the drivers side.  Pontiac intake
manifolds were the kind with the space underneath them and a separate valley
pan whereas chevys intake covers the whole valley and no pan is used.  You
can also tell pontiac engines by the fact that they are really fast :)
Pontiac engine codes are usually a two letter code found on the passenger
side front of the block just under the head.  If you email me with that
code, I can tell you all about it; head chamber size, compression ratio, cam
use, stock HP, etc.  I may be prejudiced, but pontiac engines were way ahead
of their time as far as reliability and ability.  The other great thing is;
since they didn't change the block castings from 1955 to 1981, (with minor
exceptions) dialing in the perfect combo is as easy as dialing a phone.

Curtis Mittong, Indiana, PA
96 Black Impala SS
66 Pontiac Bonneville