30 cc heads on pump gas?

[Skaterfast]

Can I run 91 or 92 octane gas if I install 30 cc heads on my twin 225 Promaxs? I will run the usual 1/2 91 and 1/2 AV gas, but if I need to run just 91 or 92 octane without hot rodding it is this ok?

[steve]

You will detonate at 91 or 92 octane. You need about 95.5-96 octane .

[Skaterfast]

What are my 1997 225 Promax heads? 36 cc? Can I go 32 cc and run 91 or 92. Keep in mind if I ever need to run straight pump gas it would be for 5 miles at most.

[steve]

they are 38cc. You can run 34cc on pump gas. If you use the #58 gasket you may like that a little better. I'd run the #58 and 34.5-35cc heads rather then the #44 and 34cc heads. 91-93 octane and you might get by with 89 at 2500 and under rpm if you get in a jam but I would not run 89 in the motor for normal use. 32 or 33 is too tight. Be sure your timing is at 25 degrees max and there are no timing advance or retard boxes on the motor.