[ItBites]

Don:

The only avgas to use is called 110LL ("110 Low Lead"). This stuff is usually blue, but can be greenish at times. Do not use red!! As I recall, the 110 is supposed to be 110 octane, but that isn't quite true (for car octane) and as I recall this has something to do with a difference from the octane rating used for pump gas being an average of the research + motor octane [(r+m)/2]. If you mix 50/50 with premium, it'll work great for even 12.5 CR, provided you're reasonable with the timing. Do not use with catalytic converters as it has lead in it. You're also warned about using it in conjunction with O2 sensors, but, while it will degrade the sensors, you'll experience lifetimes of the sensor of >10000mi even so. For most Cobras, changing a $75 O2 sensor every 10000mi would be a few years down the road.

I'm surprised the naysayers haven't chimed in. They usually post a few websites that I did find to be very informative. If you read the websites carefully, you realize that the gripes about avgas usually result in a conclusion that avgas is an acceptable, cheap way to keep from killing your high compression motor if you're just driving it around. In fact, I have seen no info that concludes any damage can be done by avgas. Most of the comparison info is related to racing and does conclude that when racing, racing gas should be used. Fine, but I'll tell ya avgas is a cheap way to drive around if you're not racing. It also smells good and will allow storage for longer without problems and will cool the intake valve and chamber. A pretty good compromise way to run around!!!

I can also add that if you change to race gas, expect to re-tune. Avgas seems to ruun pretty well with a pump gas tune