I had used the standard 307 SBC TRW flat top pistons in my 250 ( still in there) w/4 valve reliefs.
I had used the 194 cyl head to get high compression 12.0:1
Then I swapped the cylinder head to the large chamber.
I dropped the compression down to 8.4:1 ,I did not change my pistons.
This set-up was for when I ran a Paxton supercharger, 12.0:1 was a little high for a supercharger on pump 91 octane.
They are diffferent compression ratios you can pick inbetween what I had choosen & had run.
I did not leave the combustion chambers to standard size.
But @ the time I felt I had the cheapest combo to use w/out changing the pistons.
12.0:1 small chamber head, then 8.4:1 w/the large chamber head.
IIRC, the cranking compression was around 150 psi w/the low compression set-up & 220 psi w/the high compression set-up.
Back then ,,pistons were not in my budget, so I had to improvise w/what I had..
MBHD
Gee, I'd hate to think what my CR is with 80 lbs. cranking pressure!
I am willing to use custom pistons so long as they are not $200 each. That being said, 12:1 is a bit much for my needs if I end up N/A this year.
Paul
