I'm using the popular 9.4: 1 high compression map for 93 octane. Turns out the my area only has 92 octane and could drop into 91 in surrounding states. Is there any corrections I should make to the timing map? Such as retard a bit? any rule of thumb? Or is the 93 Octane tune close enough for 92?

 

General rule of thumb is to retard it one degree on a piston motor for every octane point lost until you can get it on a dyno and tune it for those specific octanes.

I would lean toward 1.5 for a rotary, only because if you do get detonation, it can mean goodbye apex seals, so would want to be more conservative until you can get it tuned properly for what you are going to use. Higher octanes have more resistance to detonation, and burn slower, so the way a flame front propagates though the combustion chamber is going to be different.

 

Did find some 110 octane race gas at $15 a gallon.

thank you for confirming there is a slight difference. What I learned was premium fuel has different definition depending on region. Yet we type out responses like it’s universal.

thank you again

 

it's possible to "make" 93 octane fuel by mixing the lower and higher octane fuels. I was thinking of doing the same when I go to have my FD tuned in southern California.

http://wallaceracing.com/octane-mix-calc.php

https://find93.com/octane-mixture-calculator#

 

That’s an interesting calculator. Not sure if I’d commit to that. I’m not competing, so I’ll drop a few hp for reliability

 

it’s always the assumptions that shoot you in the foot, or even worse, through the heart or head.
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