Originally posted by MainCap
Anybody now what the recommended maximum allowable DYNAMIC compression ratio is for 87,89,and 91 octane unleaded pump gasoline, for an iron head engine with .040 quench under towing load scenarios?

KB's site suggests no more than an 8:1 dynamic CR under the best (light load?) conditions without getting exotic. They also indicate a static CR of no more than 8.5:1 for an engine used for towing that is running on regular unleaded gasoline. I do not find how much more CR can be run with higher than 87 octane pump gas.

I can drop my dynamic CR by running a cam with a later intake valve closing, or I can choose a 28cc dish top piston that will drop my static CR to 8.8 - which seems low to me. I could also drop a cc or two out of my 64cc heads and stick with an 18cc D-cup piston for a static CR of about 9.5:1 but would 89 or 91 octane keep me out of detonation?
I think KB is right on about it's suggestions. Yes, you can drop DCR by going with a cam with a later opening or with a lower SCR by using dished pistons. You might talk with CompCams cam help line about an RV cam that would suit your towing/compression requirements. DCR is a better guide to go by than SCR because the choice of cam will delineate how an engine will run on pump gas more accurately. Normally, a performance engine with iron heads should have a DCR under 8.0. Aluminum heads can get away with .5 more. But 8.0 and 8.5 maximum numbers is figured using 92 octane. I would shoot for a DCR of around 7.75 if you want to use 87 or 89 octane.