100 oct LL AV gas
 

Does anybody have any advice on the use of this Av gas? Are there any timing or jetting changes needed for a blower motor, or will this just give me more "margin" in terms of detonation. I found this stuff a couple of miles from my house. Just swipe the card and can buy 24hrs a day at $2 a gallon.

avgas
 

I have used it with no problems with the exception the carbs started leaking around the bowl gaskets.

more octain is better! no changes needed as far as I know....ran it for years in my sled and my turbo dune buggie,Crazyhorse runs it in his camero all the time.

100LL should not require any jetting change. The vapor pressure is different from auto gas but it shouldn't affect you. The higher octane may allow you to increase the total advance but I'd be very careful. One thing about 100LL, bromide is added to promote lead deposit scavenging in the cylinders (lead/carbon deposits are a bad thing in aircraft engines) and it is highly corrosive after combustion. Another good thing about avgas is the extremely long shelf-life. 100LL has a shelf-life of 12 months with no loss of octane. Autogas is 30 days. Jim, you just needed to take that carb apart anyway.:D

I think av gas is a low lead type fuel. I run leaded 110 Union 76 racing fuel in my 13.2:1 compression motor and it works great. We tried av gas on an 11:1 iron head motor and got into detonation. Buy a spark plug viewer and make sure you're not picking up aluminum beads next to your center electrodes after some short blasts at wot. If you are seeing these beads your getting into detonation and something needs to be adjusted. The options are normally running too lean, too hot of plugs or too much timing. This tuning is what makes HP boating fun if you have the patience. Whats wrong anyway, isn't 100 MPH in a 21 foot hull fast enough for you? Good luck and be safe!

Note: I am assuming you are going to pump up the boost for a max HP and speed run.

correct me if i'm wrong on this.....but isnt AV gas "dry"? I have heard you should add some Marvel Mystery oil to it for reg engine use?

I use nothing but av-gas in my cat. I am running a blown 510, Mooneyham 8-71 blower, PFM Superchiller, Brodix heads, 10# boost at 5800 rpm. I have never had a detonation problem even when running in 120+ degree heat. I do use about 8 ounces of Marvels oil for about every 25 gallons. My engine builder recommended this because av does run a little "dry".

We used to sell 100LL (many years ago) and I had many of the same questions, so I went to Phoenix Labs in Chicago and got some answers. I just can't remember all of them. If I remember correctly the LL in Avgas is relative, it still has 2 grams per gal of lead, which is a substantial amount. The 100 octane is also measured differently for the aviation spec, and I think the R+M/2 rating is even higher.

Anyhow, ran it for years with no problems.

Just something else to ponder about the use of high octane fuels. Many engine experts claim using these type of fuels in an engine that will run "detonation free" with pump fuels will decrease HP. What do you guys think?

Thanks guys!

I just didn't want to make any silly errors that many others knew about. I'm not looking for any performance edge, just more margin of safety during the hot months. Currently running 32 degrees of advance with 8.5 lbs boost with 8.25 c.r. with intercooler.