Use of Aviation Fuel

[Tim Genovese]

I routinely add about 5 gallons of aviation fuel when I fill the tank in my L-78 with 94 octane unleaded. I have been told recently by a carburetor rebuilder that today's aviation fuel is not a wise choice and that I would be better off adding an Octane Boaster and a Lead Substitute at each fill-up.

Are there any experts out there that can shed some light on this subject?

[Joe L.]

Re: Use of Aviation Fuel

Tim----

I agree with your carburetor rebuilder. I've covered this ground before, so it should be in the archives in more detail than I'm going to go into now. But, briefly, leaded gasolines, aviation or otherwise, contain chemicals known as "scavengers". These "scavengers" are necessary to allow tetraethyl lead to be used in gasoline. However, they are extremely corrosive to carburetors and other engine parts. The bottom line is, and has always been, that lead in gasoline is GOOD for exhaust valves seats and fuel octane rating. Lead is BAD for everything else in the engine.

High octane unleaded and hardened exhaust valve seats is the way to go. A good alternative is high octane unleaded, non-lead octane boost IF NEEDED, and a lead substitute, primarily for "insurance", containing "Powershield" manufactured by the Lubrizol Corporation. Stewart-Warner Alemite, Unocal, and Red Line are at least 3 that do. I like the Stewart-Warner Alemite since it's concentrated and very convenient to carry and use.

In my opinion, folks with expensive and hard-to-replace carburetors(like folks with the Holley 3124 found on L-78 engines)should avoid leaded gas or leaded additives like the plague.

[Joe L.]

Re: Use of Aviation Fuel

Tim----

I agree with your carburetor rebuilder. I've covered this ground before, so it should be in the archives in more detail than I'm going to go into now. But, briefly, leaded gasolines, aviation or otherwise, contain chemicals known as "scavengers". These "scavengers" are necessary to allow tetraethyl lead to be used in gasoline. However, they are extremely corrosive to carburetors and other engine parts. The bottom line is, and has always been, that lead in gasoline is GOOD for exhaust valves seats and fuel octane rating. Lead is BAD for everything else in the engine.

High octane unleaded and hardened exhaust valve seats is the way to go. A good alternative is high octane unleaded, non-lead octane boost IF NEEDED, and a lead substitute, primarily for "insurance", containing "Powershield" manufactured by the Lubrizol Corporation. Stewart-Warner Alemite, Unocal, and Red Line are at least 3 that do. I like the Stewart-Warner Alemite since it's concentrated and very convenient to carry and use.

In my opinion, folks with expensive and hard-to-replace carburetors(like folks with the Holley 3124 found on L-78 engines)should avoid leaded gas or leaded additives like the plague.

[Roger Coen]

Re: Use of Aviation Fuel

In addition to the above, avaition fuel is formulated to work best at "altitude". Not sure how this might affect "on earth operation" but why take chances?

[Roger Coen]

Re: Use of Aviation Fuel

In addition to the above, avaition fuel is formulated to work best at "altitude". Not sure how this might affect "on earth operation" but why take chances?

[Everett Ogilvie]

Re: Use of Aviation Fuel

Hi. This weekend I got some new information (to me) about aviation fuel. I used to add av gas and dilute it for my L72 427. When available, I used to buy racing fuels in place of the av gas. Here in Albuquerque I recently found a supplier of racing fuel with 114 research octane and 106 motor octane. The supplier had some info regarding LL100 av gas: it is formulated to burn "hot" (most likely due to the Reid vapor pressure, etc.) for planes at altitude where cold temps and carbs are the rule. This hotter, slower burning, could be harmful to car engines. The racing fuels are formulated to burn (expand) much faster, which causes "cooling" due to adiabatic expansion (about the only thing I recall from my thermodynamic courses). The faster, cooler burning is good for our car engines relative to the slower, hotter burning of av gas.

I dilute 5 gals of racing fuel with 10 or more gals of unleaded premium, which provides more than enough octane for my 1 mile altitude, and the racing fuel has lead, and even though diluted with unleaded, there should be enough lead to protect the standard valve seats (70's leaded fuel had far more lead than what was required to protect valve seats). Hope this helps.

[Everett Ogilvie]

Re: Use of Aviation Fuel

Hi. This weekend I got some new information (to me) about aviation fuel. I used to add av gas and dilute it for my L72 427. When available, I used to buy racing fuels in place of the av gas. Here in Albuquerque I recently found a supplier of racing fuel with 114 research octane and 106 motor octane. The supplier had some info regarding LL100 av gas: it is formulated to burn "hot" (most likely due to the Reid vapor pressure, etc.) for planes at altitude where cold temps and carbs are the rule. This hotter, slower burning, could be harmful to car engines. The racing fuels are formulated to burn (expand) much faster, which causes "cooling" due to adiabatic expansion (about the only thing I recall from my thermodynamic courses). The faster, cooler burning is good for our car engines relative to the slower, hotter burning of av gas.

I dilute 5 gals of racing fuel with 10 or more gals of unleaded premium, which provides more than enough octane for my 1 mile altitude, and the racing fuel has lead, and even though diluted with unleaded, there should be enough lead to protect the standard valve seats (70's leaded fuel had far more lead than what was required to protect valve seats). Hope this helps.