The Stovebolt Site Forums The Shop Area Engine Shop pontiac 326 and 336

Can someone tell me if a Pontiac 326 c.i. and 336 c.i. engine are the same and do the parts interchange? I found a web site that says they are. If that is the case I might be able to save a little cash in rebuilding the engine in my 59 GMC.

The Pontiac 326 was produced in '67 and '68. It was the grocery-getter motor in Poncho full-size, and the base V8 in '67-68 Firebird. Usually mated to a 2-speed SuperTurbine 300. This engine has 3.718" bore and a 3.75" stroke. The main journal diameter was 3.00" All '59-'79 pontiac motors used a water pump mounted into the timing cover, a valley pan, non-adjustable valvetrain and a reverse-rotation CCW distributor. I doubt that parts from a Pontiac engine would fit any other engine family.

If you find out otherwise, please let me know.

Good luck

Chip

I sent the information over to my dad, who has been in Pontiacs since the early 50's. This is what he came up with.

I found proof - the 1963 326 Pontiac engine was indeed 336 ci.
And '63 was the first year it was used in the Pontiac cars. My
Sealed Power catalog lists this:

326 Engine:
1963 Bore was 3 25/32" which is 3.781 and the stroke is 3.75, for
a displacement of 336.8 ci.

1964-67 - Bore was 3 23/32" which is 3.719, and the stroke is
3.75, for 325.89 ci.

We have been associated with Pontiacs for many years, and have
good reference material on them. The first year for the Pontiac
"326" engine in a Pontiac car was 1963. That engine was actually
336.8 cubes with a bore of 3.781 and stroke of 3.75.

The Pontiac "326" engine used from 1964 to 1967 (last year of use)
had a bore of 3.719 and stroke of 3.75 for a displacement of
325.89 ci.

We are not positive the 1963 336 ci was identical to the GMC 336
but believe it was. Many other parts other then block and pistons
would have been identical between the two engines.

If you need more help, let us know. Joe

Hi Joe,

That is some good info! I wrench corrected.

How come none of my books or websites I found list a 326 for 64-66? All I find for '60-66 is a 316, 347, 370, 389 or 421 motors. Was '68 the last year for 326, or first year for Pontiac 350?

I thought that each division of GM had its own powertrain engineering group until early 80s? I didn't know many parts would swap between Poncho, GMC, Olds, etc.

Is the crankshaft the same between a 326,350,389 and 400? 3" mains, 2.25" rods, 3.75" stroke?

I also got that email you sent. I enjoyed the pics of that LeMans racer!

Good luck

Chip

I had a "326" '63 Tempest in college. Had that goofy swing axle trans/axle in the rear with a 3 speed. Pretty quick for those days & only a 2 barrel carb. Rear suspension was majorlly squirrely and as I recall it had one rear brake that would only quit self adjusting when the wheel was locked up. Always had to budget enough "klicks" in before going out at night to cover the number of back ups one might do during to coarse of an evening.
We'll call that "Generous Motors, the Developing Years"......

The cranks on the small engines are all the same size. The material and quality differ through the years. The 67-70 400's were the better cranks. The newer 400 got a little weaker as the years went on.

I don't know why the books don't list the early 326, none of my did, but I remember seeing the 326 badge on the Tempest.

Pontiac parts will only work in Pontiac engines, the GMC used a Pontiac engine for many years. The early years it was the 6 cyl, then the V8. Joe