High Compression

[Terry Petty]

Is there a "sellers" or "wanted" section on this forum? I'm thinking a set of 250HP 2bbl 70 cc #62 heads would be good to bring my compression down to around 9.3:1 on my 65 326 HO (10.5:1CR).

#76 and #77 389 heads with 70cc have slightly larger valves, 1.92" and 1.66", but not sure if they would create interference with the cylinder walls.

I see a 67 326HO uses these larger size valves (just for comparison), but I think at a different valve angle. But I believe the 67 and up also space the valves wider so I'm wondering if the 76's and 77's will clear on a 326.

 

[melsg5]

I think you should contact this company with your question. Their chart seems to show that you would lower the compression to 8.6:1 with the number 62 heads.

http://www.wallaceracing.com/head1.htm

 

[Terry Petty]

I'm basing my numbers on pure mathematics. If my engine is 10.5:1 with 60cc #22 heads, and I install 70cc #62 heads, I come up somewhere around 9.3:1 on my engine. These numbers for the heads came from Ron's Pontiac Pages.
http://ronspontiacpage.com/reference-pages/stockheadspecs.htm

I've already seen that chart, it states that the 250HP engine has 8.6:1 compression, but does not say if the pistons are different.

The question about the 389 heads and whether or not the valves will clear on a 326 stock bore is till pending. Any idea about that, anyone?

 

[melsg5]

I gave you the link to Wallace racing to ask them about the clearance issue with the larger valves. You could also check a book that covers Pontiac engine rebuilding.

https://play.google.com/store/books...US&gclid=CIjqrIyHpswCFYZXNwodYkEH0Q&gclsrc=ds