This is not about my RX7, but my dirt bike. I posted here because I think I might get a better answer then in the lounge. I own a KX125 with an engine built by RPM Rick Peterson out in California. It is 139cc, ported, and runs on race gas (110). With the price of race gas, almost $6 a gallon, and the fact that I have to drive 50 miles to purchase the stuff, replacing the top end to run on 93 octane is in the future plans. But until then, I came up with another idea.

When I last purchased the race gas, all they had was 115 octane. I was told to use 110 octane in the bike. I was thinking that if I add 1 gallon of 93 octane to 4 gallons of 115, the octane I came up with is 106.6. I just did this buy averaging the octanes together.

Because of my amateur level of riding skills and the fact is the bike has a ton of power that I don't use, would it be safe to cut the race gas to a lower octane to save money?

 

I would suggest talking to the engine builder, it sounds good, but he might have specific reasons for the 110 octain, and he might have ideas on how to cut some of the costs.

 

You are right, Averaging does work.

 

Give it a try and see how low you can go before performance craps out.
Responsiveness will decrease.
With my stock YZ250, for races I mix 50/50 110 race fuel to 93octane.

 

That does not sound right, unless you have an OBDII ECU. Otherwise, you lower octane will light more easily, and will give you an almost undetectable improvement, until you detonate. Progressivly lower octane is a bad idea IMHO. If the motor is designed/set-up to run with 110, you will need to change timing to be ableto runa signifigantly lower octane. Keep in mind Pre-mix als lowers octane, but I am sure that was taken into account on the octane recomendation. Good luck, Carl