[goatwgn]

Originally Posted by b-man

Over square - bore dimension bigger than stroke, all Pontiac V8 engines fit this description with the exception of the 326 and 455.

Under square - stroke dimension bigger than bore

Square - both the bore and stroke dimensions are equal

The 455 only needs to be bored approximately +.060” to become ‘square’ (4.210” x 4.210”).

Same thing goes for the 326 with the factory 3.72” bore and 3.75” stroke but only needs to go +.030 over bore to be square. Funny that in 1963 which was the very first year of 326 production the bore was actually 3.76” for some reason and was then reduced to 3.72” for 1964 through the end of production in 1967. Great little V8 which might be the one with the highest reliability and longevity of all Pontiac V8s.

Both of these slightly under square Pontiac engine offerings are excellent street engines for their intended purposes, neither one should be overlooked when either big torque in the case of the 455 or excellent economy in the case of the 326 is desired.

Some here might be surprised to learn that many if not most of the big-cube Pontiac race and street engines are under square. With bore sizes under 4.40” for most and strokes 4.50” and larger Pontiac engines don’t necessarily need to be over square to be great racing or street engines.

I agree on the longevity of the 326. My '66 326 2 bbl went pretty trouble free for 292000 miles, when I pulled it (still running well, but a bit weak) in the late 1980s for a 455, which in itself went 100000 miles, of hard use, and the only reason I pulled it to redo it in 2011 was to reduce the compression to be able to run it trouble free on low octane gas. I was running the old 10.5 to 1 engine with a mild cam with dialed back timing, and octane boosters.