Replies to This Discussion

Permalink Reply by Peter Eiberger on Tuesday

I would avoid octane booster as it generally comes in two forms: tetraethyl lead (might as well run avgas) or MMT. The MMT will leave brown/orange deposits inside the engine and spark plugs. These deposits can cause harm over time.

You are better off running avgas with some decalin, or mix avgas with your 89 octane pure gas. DON'T mix leaded gas with ethanol gas. 

• ▶ Reply

Permalink Reply by Cody Furlow on Tuesday

Thanks, I was thinking about mixing 100LL at a rate of 1 gal per 5 gal of regular gas not ethanol gas. Does that sound like a good mix?

• ▶ Reply

Permalink Reply by Paul Bonasera on Tuesday

I was wondering why you say not to mix Ethanol gas with 100LL? I have been doing it for years without any problems.

• ▶ Reply

Permalink Reply by Peter Eiberger yesterday

 Long story short, TEL (lead) lowers the octane rating of the ethanol. Common question on racing forums about mixing e85 with leaded gas.

Some info copy/pasted below. Book being referenced is Internal Combustion Engines by Edward Obert

You guys need to know that the metallic additives used to raise the octane of gasoline lower the octane of the alcohols. TEL, TML, and MMT are pro-knock in behavior with methanol and ethanol and probably the other alcohols as well. I don't know for a fact, but I strongly suspect, that MMT is significantly pro-knock in alcohols. I've seen and been told of engine wrecks that I know had methanol and MMT involved (and TEL in one).

In Obert's book he shows the R/M octane numbers of methanol as 106/92 and ethanol as 107/89. The addition of 3ml TEL per gallon of ethanol lowers the 107 to 102. You decide what this means to you when you mix leaded race fuel with alcohol.

• ▶ Reply

Permalink Reply by Paul Bonasera yesterday

Well, I normally run Auto fuel with 10% Ethanol in my planes. When I travel and have to refuel, I buy 100LL. The only problem I have ever had is lead fouling on long trips and the 2 months of having to clean the plugs after all the Leaded fuel is gone. When I was still riding dirt bikes, my bike (CRF450R) ran best on a 50/50 mix of 100LL and 91 Oct auto gas with 10% ethanol.

• ▶ Reply

Permalink Reply by Peter Eiberger 22 hours ago

Try some decalin lead scavenger when you run 100LL. It keeps lead from building up in the combustion cylinders and spark plugs. Decalin is recommended by WW Flycorvair, Viking, and others when running 100LL. You can get it from spruce

• ▶ Reply

Permalink Reply by Paul Bonasera 19 hours ago

I did read through that. I believe it could be a problem if mixed with 100% ethanol, but at a 10% mix, I don't see any issues.

• ▶ Reply

Permalink Reply by Jim MacWilliams yesterday

The recommendation I received from UL Power at Sun&Fun this year was to use 93 unleaded with ethanol such as Shell's V-Power assuming all hoses and connections were ethanol resistant. If I was on a cross country, go ahead and fill it with 100LL and return to using 93 VPower when I return home.  No issues with mixing the two so said UL Power.

My plane, a CH650B, has ethanol resistant hoses, except for the blasted fuel senders.  Ethanol over time will dissolve the center connection to the fuel sender.  I have replaced the original fuel senders in mine with Stewart Warner fuel senders and sealed them with Van's fuel tank sealant (MC-240-B1/2).

• ▶ Reply