Interesting subject.
Here's a thread I stole from the Cobra web site:

If your engine is properly tuned for use on pump gas, and you switch to TRUE aviation fuel, you can be nearly assured that you will detonate and potentially cause serious harm to the engine!

Please allow me to explain in detail why this is a problem:

An internal combustion engine's fuel requirement is determined by its Brake Specific Fuel Consumption (BSFC). By definition, the BSFC is the amount of fuel required per horsepower to properly run an engine. As a rough rule of thumb, most moderately built naturally aspirated street engines have a BSFC of about .5. This means that the engine requires .5 lbs/hr of fuel per horsepower. So if you have a 400 horsepower engine, the formula would be as follows: 400 x .5 = 200 lbs/hr fuel requirement. Notice that this is figured as a weight of fuel and NOT as a volume of fuel!!

The specific gravity of any element is determined in relationship to the weight of 1 gallon of pure water which is about 8.33 lbs. “Pump gas” has a specific gravity of about .72. To determine its weight, do the following: 8.33 x .72 = 5.99 lbs per gallon. (Technically, gasoline is rated at 6.009 lbs @ 72 degrees Fahrenheit).

The specific gravity of “Av-Gas” is much lighter than pump gas! It usually has a specific gravity of about .61 to .64 and weighs around 5.3 lbs per gallon. So you can see that the same volume of Av-Gas weighs dramatically LESS than “Pump-Gas!!” Remember, your engine needs a certain WEIGHT of fuel, NOT a volume of fuel. If you switch from “Pump-Gas” to “Av-Gas” and you do not change the jetting or injector size to compensate for the fact that the weight of fuel being ingested by the engine has been substantially reduced, YOU WILL RUN THE ENGINE LEAN!!

Let’s go back over that formula from the beginning of this Nerd-Like reply:

A 400 horsepower engine running on gasoline has a .5 BSFC.
400 x .5 = 200 lbs/hr fuel requirement
If “Pump-Gas” weighs 6 lbs per gallon, the engine needs:
200 / 6 = 33.33 gallons per hour.
But if you are running “Av-Gas” that only weighs 5.3 lbs per gallon and you do not make any changes to the jets or injectors, you will continue to receive the same VOLUME of fuel but will run lean determined by the following:
33.33 x 5.3 = 176.6 lbs of fuel

Now we go back to the 400 horsepower engine with the .5 BSFC requirement. It needs 200 lbs/hr, but it is only receiving 177 lbs/hr. So your actual BSFC ends up being:
177 / 400 = .44 BSFC

So now your engine that requires a .5 BSFC is only getting a .44 BSFC. This is very dangerous! I have heard claims by some that when they put “Av-Gas” in their engine, it makes more power—and this is very possible; A lean engine WILL make more power because “Heat is Horsepower.” But just remember:

TOO LEAN, TOO LONG, TOO HOT, TOO BAD!!!

Sorry if this reply is more detailed than necessary. It’s just that I have had an extensive amount of experience with this subject and I felt that this would be an opportunity to hopefully clear the air of some of the many myths, half truths, and sometimes just plain old wrong information. I hope that you realize with the extensive detail, you will see that I intend to EDUCATE rather than “brag” to people that I don’t know.