The highest Octane I can buy locally is 91. The car is tuned for 93-95 octane. How much do octane boosters actually increase the octane rating? You read where it says 2 to 3 points. Does that mean from 91 to 93-94 or does it mean from 91 to 91.3 or 91.4??

What brands work best? What about adding aviation fuel (100 octane) to the 91 pump gas, like 5 gallons of avgas to an empty tank then fill it up with 91 octane?

Any suggestions?

 

I believe it takes ten points to raise it one octane number.

 

that is correct. a point is .1. so if it raises the octane 7 points from 91 octane it would be 91.7 octane

 

If it is a street car any you cannot get 93 octane in your area, then I suggest retuning the car for 91 octane. You will need to retune your fuel computer or EMS if you mix 91 octane with avgas, xylene, toulene, etc., so you may as well just tune your computer for something that is easily available like 91 octane. You can always just retune for race fuel at the race track when you need maximum performance.

BTW, 100LL avgas is loaded with lead, and is technically illegal to use on the street.