Rich Sandor

100LL / 100 octane low lead aviation fuel (avgas)

How would it hurt the engine? What does the lead do that's bad. Does the relatively high octane level offset the small amount of lead? or do lead deposits destroy the innards of the 2.5L?

I have acess to avgas for much cheaper than what it costs, and I'm just wondering.

fast951

The lead will destroy your O2 sensor, and the cat converter. The main problem with using avgas is its density.
The avgas has a lower density than automotive gas. Which means, your car will run leaner. You can tune it to use avgas, but you'll be replacing O2 sensors often... Unless you tune the car then take out the O2 sensor.
I strongly discourage you from running avgas by itself in your car. A mixture is always recommended.
After you compare the pros and cons, I think you'll decide not to use avgas.

Alan C.

If it is a track only car I'd consider looking into avgas if I had a stand alone system. As fast951 noted you need to be able to tune for the change in density. I've thought about doing a Tec3 file for avagas this summer.

Alan

Rich Sandor

Does the lead harm anything in the combustion chamber? I'm guessing the stuff doesn't exactly burn along with the fuel, so there would be lots of deposits throughout the cylinder walls and what not. If so, is that harmful?

Could I run the car without a Cat and o2 sensor?

fast951

A standalone engine management is fine, however the change in density is amout 15% or so, you might be able to run the mixture a bit richer by upping the fuel pressure. But not ideal! Also, make sure you mix it with regular gas.
I ran it on my car as a mix for few times while on the track, now I just stick to race gas.

For a street car, I recommend you keep the O2 sensor. For track use, you are a WOT most of the time and outside the closed loop so the O2 sensor can be removed. I personally like to keep the O2 sensor on my race car as I use it for my AF meter.

One more thing to look into, is that lead works as lubricant. I doubt it'll damage the valve seats, but someone else might want to shine in on this one.

Bill

The only thing I am aware that lead will impact in the combustion chamber, is the spark plugs. In the days of leaded gas, spark plugs did not last as long as they do now. The lead would deposit itself onto the plugs and eventually foul them.

The leaded gas formula did several things. One was to boost octane and thus reduce detonation. Another being that lead was used as a cushion for the valves and seats. When lead was legislated out, this was the biggest impact on engines designed for leaded gas use. On new cars, the manufactures hardened the valves and seats. Older cars had to have the hardened valves/seats retrofitted. So to get back to the question, there may be a chance of the lead fouling the valves/seats. However this is just conjecture on my part as I have not seen a newer car that has been run on leaded fuel for any length of time.

I have also never seen a turbocharged car run on leaded gas (automotive turbo technology came after lead). Given that one of the adverse caracteristics of lead was that it would deposit itself onto surfaces it contacted, Then perhaps it could also gum up a turbo or a wastegate. Or anything else in the intake/exhaust system that you can think of (like the guys above stated, O2, Cat, etc.).

Alan C.

I run my turbo on leaded gas. No problems with valves, seats or turbo. I don't use the O2 sensor and the car is not programmed in closed loop. The O2 sensor has no authority on any fuel calulations.

Alan C.

Dave951M

Why, when you can get good gas at the track or-- mix your own.

MachSchnell

I've seen this discussed quite a bit by a buddy at nasa (well, Lockheed Martin as a contractor for NASA but you get the point) with regard to turbo japanese cars...apparently the biggest issue with avgas is a very severe lack of consistancy among quality control...I guess the setup of the aviation engines don't require quite the same levels of consistancy with regard to fuel quality/octane, and quite a few guys had tried this and failed at the track due to detonation after the first tank of gas ran clean as can be, and the second pinged the whole way down the quarter...basic answer, it's a helluva lot cheaper to invest in the true leaded at the track for days when you need it than replace parts of the motor if the batch you get ain't so hot...

Sumflow

Quote:

Originally Posted by Bill

I have also never seen a turbocharged car run on leaded gas (automotive turbo technology came after lead). Given that one of the adverse caracteristics of lead was that it would deposit itself onto surfaces it contacted, Then perhaps it could also gum up a turbo or a wastegate.

Leaded gasoline was phased out in the US from 1975 - 1986 . In 1965 Chevy had a turbocharged 164 cubic inch, aluminum alloy, “ pancake” Corvair engine. The turbo was rated at 180 horsepower @ 4000 RPM. Probably ran on gas available at the pump.

Tedro951

My experience with Avgas is in aviation, but my opinion is that if an engine doesn't need the octane, it is better suited to lead free. I would buy that the lead is good for valve stems/guides, but it doesn't seem to pan out in real world experience. All of the smaller continentals (and probably big ones) seem to love Mogas and its ability to give long, trouble-free life to valves. I will confess that when breaking in a new off road engine, I mix 100LL and premium auto for the first tank.

Paulyy

I know this thread is old.. Just so you know.

My dads 924 was designed to run on 98 octane Leaded fuel. When it was phased out in Australia, it was replaced by "super unleaded" which is now just 98 unleaded. When my dad made the change, the whole engine went up to ****. The mechanical fuel injection didn't work properly and the car never ran the same.

my 951 (952) was designed to run on leaded also. I know this because it has a resonator instead of a catalyst converter (after market cat in the wrong spot). No Unleaded stickers anywhere. DME in closed loop (which late last year the DME for the first time saw an o2 reading) and the damn fuel pump nossel doesn't fit into the fuel filler hole properly.

Not sure about the valve seats though.

Grandpa#3

As poor airmen back in the early 1960's we ran our cars on a half and half mixture of regular leaded and 115/145 avgas. We never had any problems out of our car engines.

Cheers,
Larry

Turbo17

Surprisingly, the 100LL avgas currently available has about four times the lead that regular leaded mogas used to have - despite being called "Low Lead".

Edrtith

I will confess that when breaking in a new off road engine