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..


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