Curious if using avgas 100LL would be good, bad or ugly in my F-Type S? Benefits? Risks? Waste of $? Thoughts?

Please be nice if this is the stupidest question of the week… lol.

 

Your cat converters wouldn't like the lead content.

Cheers
DD

 

yeah… Thought that might be an issue…

 

Generally on a car tuned to run the 100LL you assume the cats have been removed.

As a default, increasing the octane will not gain anything unless you are octane limited. You'd be better served by mixing some E85 in there, it's effectively about 105 octane, a slight blend to bring your tank to E25-30 is a similar boost in octane but often won't push the car lean enough to cause issues.

Are you just doing it for fun or is there a goal here?

 

We can get 101 un-leaded ($9.50 per gallon). But like said above, unless you're octane limited it won't make any diffrence.

 

In addition to the cats, the O2 sensors also dislike leaded fuel.

If the goal is knock protection, 100 octane unleaded is available.

 

I actually live closer to 100ll than high octane fuel (I live on an airport), so I wondered if this was an option. I get it at just a bit above cost, so while there is a price difference, its not much.

 

There's much more to 100LL. It's aka 100/130.
At Lean A/F typical Octane is 99.6-102
At Rich A/F typical Octane is 130-132
Modern avgas is very different from 30 years earlier. Commonly held beliefs just ain't so.
The Tetraethyl-Lead density is currently limited at <0.56 g/l, but production avgas ranges from 0.36-0.50 g/l
Lead deposits in engines no longer exist, that was fixed decades ago. The TEL is reduced to Lead Oxide during combustion, this reaction increases Octane. They've added Ethylene Dibromide to scavenge Lead Oxide which forms Lead Bromide >>> Exhaust Gas. The lead oxide >> Ethylene Dibromide affinity is remarkably effective so Lead Oxide doesn't leave lead deposits behind. I've scoped and opened many engines and have never found visible lead deposits.

These engines are 550CI, Twin Turbo Charged, Twin Intercooled, Fuel injected, air cooled, 300HP at 2800 RPM continuous duty up to 25k AMSL and live 2000 Hours until OH.
The pilot has dash mounted controls for A/F ratio, Manifold Pressure, with Ex Gas Temps per cylinder displayed. The Pilot will tune A/F for peak power, then Lean Fuel known as Lean of Peak, for best economy, 100 Octane. Or the tune can be Rich of Peak where manifold pressure can be increased, utilizing 130 Octane.

Why it matters here... because those who play with 100LL avgas fully miss the point. Guys run 130 Race Gas at 3 ATM. That's not simple to do, but if you could just run avgas rich around 11:1 to allow +1 ATM boost, that'd be the bomb. Avgas power drop Rich of Peak is insignificant. Maybe add a big timing advance, 2x SC RPM, a load of Methanol and/or Water, lots of fun to be had.

 

Back when I raced, I watched people throw away money of high octane gas all the time. They would think higher octane meant better performance, but if the motor wasn't tuned to the high octane, it would run worse, and that was with unleaded. Add lead into the equation and the car would run horribly and you would have to buy a series of replacement parts that don't play well with lead.

 

Your car would need to be tuned for higher octane, with a base tune it would be useless and could even hurt your engine.

 

Almost everyone clings to commonly held beliefs; most were true in the 60's or 70's.
I may not have clarified well. 100LL avgas has evolved substantially since long ago.
I shared the TEL density common now, I guess that was too obscure. TEL density is very low. More importantly decades ago, they added scavenging agents to carry the Lead-Oxide out with the exhaust.

In short, I doubt modern 100LL could lead foul anything when used for weekend drag fun. Many Aircraft piston engines have O2 sensors for Pilot information. That's the only fuel they use, and lead deposits have been effectively eliminated.

It's very true that Octane too high for the CC pressure will reduce engine power output below the correct Octane fuel. I could never feel the change, but a couple percent always shows up on finish line speed, and on the dyno. If you can add CC pressure, like with a waste gate, you'll get to burn more fuel; that's a great reason to increase Octane.

I've never seen this error break an engine, but it wouldn't surprise me.

 

your question is the opposite of stupid. It's stupid to pump avgas in to see what'll happen without at least asking.


I've watched mine hunt for most efficient ignition advance. It'll advance until knock is sensed, then retard just enough. It also hunts for leanest A/F limits. Very sophisticated controls. They do this to allow your trip to continue when the station has only 87 for sale. The range for these hunts probably does not extend up to 100 Octane, but I wish I knew.

 

In the summer of '88 and the summer of '89, I worked at RHV as a line guy. 95% of my job was driving around a big gas truck and refueling planes. There was one old guy with a 60's mercury that would have his tank filled with 100 LL and he was the one and only exception to no 100 LL in cars rule. Even back then it was drilled in that we were not to take on the liability of putting 100 LL in cars as the avgas would destroy catalytic converters in one tank. A weekend of use would absolutley destroy things. Many airports have self serve pumps that you could drive right up to and I'm not sure how they would handle the liability.

The vast majority of general aviation planes do not have O2 sensors. There really isn't a need as you have manual control over so many more aspects of the engine. You spend time getting the engine leaned out just right for your altitude, curise speed (RPMs), etc. You don't have that in cars, where the computers rely on many things, including the O2 sensors. I personally have never flown a plane with O2 sensors as those were too new to be in my budget, so I can't speak from experience about the process for checking them and cleaning them. I do know that it's not the same as a car, though, and the O2 sensors in airplanes also have a much shorter lifespan and are designed for use with 100LL.

 

O2 sensors don't control things, can be dash mounted dials, or just push data to a data storage, maybe now to an app.

Allowable TEL gets a fresh government reset when the producers lock chemist in a closet long enough to reduce. The produces report as required and have to serve up their secret sauce. The TEL is much lower, but more effective is the scavenging agents. There are a few, and the struggle continues. I've only seen a couple O2 reports. Guys with constant speed props and twin turbos think they are cheap. It'll identify one cylinder in-trouble during live operation, so that's cool. You could save an $90k engine, by finding the bad $8k Cylinder.

Whatever happens, or doesn't in an aircraft, will not likely repeat in an auto engine.

 

Unleaded nozzles were built with a smaller diameter and cars built for unleaded had a restrictor in the fuel filler neck to only allow that, and not the larger leaded nozzle. Part of the regular emissions testing here was to check for the restrictor with a standard metal rod, which was required to not fit.