Cory M

We have a couple of Carrera racecars that run on 100 octane race fuel. We always used to mix 110 leaded with 91 octane pump gas with a 1:1 ratio to achieve the right octane level. The main reason for doing this was to save a few bucks since the 110 leaded and 100 unleaded are the same price at the track (no one out here sells 110 unleaded). The engine runs good either way. A respected mechanic who specializes in air cooled 911's said that we should only run the unleaded and not mix. He said the leaded fuel was bad and something about the spark plug threads galling, I'll ask him more next time I see him. I was wondering if anyone had any info on the negatives of running leaded fuel? Between the 2 cars we burn up a lot of fuel on a race weekend and not mixing the fuel can potentially add hundreds of dollars in cost to the race weekend.

Matt Romanowski

Lead is usually considered an upper cyclinder lubricant, so the galling makes not sense to me. I've never heard that as a problem with leaded fuel either.

Depending on the fuel, they have different burn speeds and other properties. I don't see any problem with mixing it.

Kurt R

I think he has that backwards. If you aren't running cats or O2 sensors there's no reason you can't use leaded fuel.

amso3

We had an issue at Sebring this past weekend at the PCA club race, they ran out of 98 unleaded. I spoke with a PMNA engineer to discuss our options: 91 unleaded or 110 leaded. He said to go with leaded, but it would probably foul the O2 sensors. Luckily, we only needed about 4 gal in each car so no problem. I expect that spark plugs in aluminum heads would have anti-seize on them so I doubt galling would occur

MUSSBERGER

I would think if that much lead got up in the threads you would have bigger problems than just galling.

Bailey-86-MA

I have run 112 leaded race fuel for 5 years with no problems. No cat or O2 sensor.

Matt Romanowski

It's not the top of the threads you have to worry about, it's the bottom near the combustion chamber. But, lead won't cause that much in the way of deposits. Especially on the threads (if they protrude).

Steve Weiner-Rennsport Systems

Nothing to be concerned about; use your current mix in good health. Quite obviously, if your cars are running O2 sensors in closed-loop, they will not last long using leaded fuels, but you can deal with that by monitoring Lambda voltages.

I do use a tiny bit of copper-based anti-seize on plug threads to prevent any damage when they are extracted.

Cory M

That's good to hear. Thanks everyone for all of the feedback. I'll ask my mechanic about it again, maybe I misinterpreted what he meant.

JBreckeen

2 points:

1. I have been running strait 100 octane AvGas (very leaded!!!) for several years now, and it has not even killed my O2 sensor - yes, no cat. I have seen zero problems contributed to the AvGas or lead in the engine, spark plugs, electronics, etc. . . No detonation, no slow burning, no fouling, basically none of the problems that fill the internets forums full of second-hand information.

2. 100LL in airplanes - there is so much lead in AvGas, and these engines are so underworked (ie 360 cubic inch, 8.5/1 compression ratio, max RPM 2700, 180 HP), that when you pull the plugs out, there can be chunks of lead in the threads and head of the plug - sometimes causing a dead-short across the plug.

So in my experience, lead is fine for cars without Cats. But, as usual - your milage my vary!

Good luck . . .