Don't Substitute Aviation Gasoline For Racing Gasoline
Don't substitute Aviation Gasoline for Racing Gasoline unless your race engine operates at 10,000 feet altitude, and does not exceed 2,800 RPM.
Many racers see Aviation Gasoline (AvGas) as a way to reduce the cost of their racing operation. This may be true, but if you want the most out of your engine and want to avoid problems. AvGas may not be your first choice. AvGas is a good gasoline for low speed aircraft engines that run at 2,700 to 2,800 RPM at 10,000 feet or higher. This does not mean it is a good gasoline for racing engines operating at 8,000 to 10,000 RPM. AvGas is also illegal to use in anything except aircraft engines. Violations can carry a potential penalty of $25,000.00 per day of violation.
AvGas octane numbers are determined in a different test than motor gasoline octane numbers. Do not be confused by the big numbers from the AvGas test method. They are not comparable to motor gasoline test numbers. The 110 leaded gasoline will test out at about 160 on the AvGas scale.
AvGas is held to tighter requirements than street gasoline, but not nearly as tight as is the entire line of Racing Gasolines. Some racing gasoline blenders us AvGas as a blending component to save money.
AvGas has a lower specific gravity than most racing gasolines. This means that if a racer tries AvGas and has not re-jetted, he can burn a piston because the air-fuel ratio is too lean and/or the engine detonated. To make a good comparison between two gasolines, the air-fuel mixtures must be the same. Even after re-jetting, the racer can experience burned pistons with AvGas if the Motor Octane Number (MON) is lower than what his or her engine needs.
Another potential problem with AvGas is that there are several different octane grades. The 80/87 grade is red in color and can get you in lots of trouble because of its very low octane number. The 100LL is blue and the 100/130 grade is green. Both of these have much lower Motor Octane Numbers (MON) than most racing gasolines and will detonate when the engine octane demand is greater than the octane number of the gasoline.
The bottom line is: Feed that high dollar racing engine a good grade of gasoline so it will deliver the maximum performance. Don't use "low bidder" mentality.