actual compression ratio

[hensho]

anyone know what the actual compression ratio is of the early sho's.
my 89 seems to run fine on the middle grade gas with no apparent pinging.
i think the octane of this gas is less than 90. should i be using the highest octane available? octane additives? hensho

 

[Off Road SHO]

I believe it is 9.8:1. If you don't hear pinging when you place a load on your engine AND you have good hearing, just run 87 or 89. If you plan on running her hard (loading the engine), stick with the 91+.

Tom