Johns vette

Just took a comp test on my newly rebuilt 76 350 L-82 s/r world heads and isky cam and got 6 with 170 lbs. and 2 with 180lbs. Before the rebuild all 8 were between 138 and 150lbs. Any ideas what octane I should be burning?

Gordonm

The cranking compression has nothing to do with your compression ratio. It is just telling you that all the cylinders are fairly equal and you have a good seal. The place that rebuil your motor should know what compression ratio you have. If you have aluminum heads you might get away with 10.5 to 1 with pump gas. Iron heads maybe 9.5 to 1. You could retard the timing but that will lose power. Take it out and if it starts to rattle and the timing is correct try a little booster.

Nomad78SA

John,
Pick up a copy of the new issue of Car Craft. There is a article on that very subject. You need to read it all but had a small chart
8:0:1=cranking pressure 135
9:0:1=163
10:0:1= 195
11:0:1=232
Neil in Tenn

nunus79

I have 185psi and have run as low as 89 octane on the street with no apparent problems. I don't know if I can run lower octane because I never tried.

8T1-7T9 BIONIC VETTE

Nunus79,
I'm running 180 psi on all cylinders....what's my compression ratio?

nunus79

DAMN GOOD :D

Seriously, it is virtually impossible to back calculate compression ratio from cranking compression. Cranking compression measures your static compression, general cylinder/valve condition & cam timing. The 180 is respectable.

Johns vette

Thanks for the info people! :seeya