Have used Av. gas. Yes, very expensive and can only get at airports. Not always the easiest to come by. Unless your engine is very high output and used for racing, you wouldn't need it. 

There used to be 3 octane levels of Avgas, 80, 100, 130, all of them leaded. Now the only common Avgas you'll find is 100 octane low lead. It does have a tiny amount lead in it but not alcohol.

Hi to everyone,
They are heavier for the same power, because they need to be made from stronger material due to the higher compression ratio and because they need to have larger cylinder volume because of lower maximal rpm. On longer flights the reduction in fuel weight often makes up for the heavier engine.

As we used to say in my line of business... the answer to any question is "it depends..."

I can see two basic reasons why you might choose to use avgas..  

1.  It MAY contain lead..  IF you run normal valve seats this MAY be a benefit; although there are lots of alternatives (at a much cheaper price).

2.  IF your compression ratio demands it, avgas usually has a higher octane rating than normal pump gas. (Again, there are alternatives).

IMHO, just take your car to the local gas station and top it up with whatever additives your car actually requires.

Cheers, Ian

It depends on which of the common avgas you're talking about. We use unleaded 94 avgas in our boat due to the lack of alcohol and the extended shelf life, the motor is modern injected/computer controlled so maybe it can benefit from the higher octane but we use it mainly because it doesn't have alcohol. I've never tried it in the mini but have run VP unleaded alcohol free "race" gas which works well. If I wanted to use UL94 avgas in the mini I would need to fill gas containers, as the airport won't allow direct automotive filling. The standard 100LL (low lead)avagas I believe has less tetraethyl lead than the old leaded automotive gas and probably wouldn't benefit a mini that has hardened valve seats and standard compression. If you have really high compression it would probably help it. Oh and the stuff is expensive last time we got UL94 it was $5.50/gal

I use Chevron 94. The pump says no methylene with no.

Within the past two weeks I have spoken with 2 long time mini owners (one a mechanic).  Both touted the benefits of using aviation fuel in minis.  I am looking for more information re: pros and cons of aviation fuel.