im under the impression that i should tune the car on the octane i run most of the time, 91... or should i tune the car for 100oct or c16??

 

Get the car tuned for the lowest octane that you drive it with...Why would you tune for 100 octane when all you have is 91? Do you want to blow your motor?

Tuning for 91 and driving on 100 won't hurt your car, tuning for 100 and driving on 91 will.

Don't tune for anything less than 91, or better yet, 93 if it's available where you live.

 

Your first assumption is correct. Tune the car for what gas you will be using. Make sure to use new spark plugs for your tuning.

 

ok... just making sure, i hear all these people with stupid numbers on 100oct or c16,... I only get 91 around here for the most part, can also get 100 but the price is to crazy now.

 

You can tune with high octane fuel as a safety net, you'll have a little more margin for error if you have conditions that would typically be unfavorable (lean mixture, and/or too much timing, too much boost, etc.) on a lower octane fuel.

The thing I don't like about tuning on race gas (my defn of race gas: higher octane fuel you seldom run in your car) is if you're looking at knock levels and call it good and then go fill up with 91 and then suddenly you notice a big increase in knocks... that could be a problem.

Tune the car with the gas you're going to be running