Can i run 100% AVGAS 100LL?

[33 IMP]

Kiwi nailed it in post#33. Michael, if you're worried about the valve seats, and don't need the higher octane cause your car runs good on pump gas, just a few liters, maybe four per tank, will do what you want, and not change the tune at all.
I run the avgas, in the percentage I do, for a couple reasons. 1. My engine is on the ragged edge of running on pump premium. 2. I can get it in Arizona for LESS money than california premium, it has lead for the seats (not really a concern in my case) and raises my octane rating several points.
I have found no reason not to run it in my case.

 

[Cranky]

No not straight av gas. If you fill the tank the car will run bad, too lean. The specific gravity is way light compared to pump fuel.

You can add some to each tank as said above, and you don’t need it in every tank so you can take a trip with pump fuel without worries.

like 25% av gas Is plenty.

dont fill the tank with av gas. You will be very upset if you do, anyone that tells you to do it has never done it or was way over jetted and the car ran like crap on pump gas. You have been warned! LOL

I've run av gas for a lot of years and didn't experience lean conditions. How high do you have to fly for the specific gravity to make a difference? Most guys I know with small planes don't fly much above 1000 feet and some never do. My last time up with someone and he was staying at 900 and I motioned for him to take it up 300 more so we could get into cooler air temps. Made no adjustments and the engine didn't miss a beat. But I agree with not having to go with 100% av gas....

From my own experience, whatever ratio avgas you decide on, you have to run that CONSISTENTLY or the car will run like ****. The specific gravity is so different than pump gas that its absolutely necessary to tweak the carb(s) for the mixture. If you alter the mixture it will have a noticable effect. What this means is that you'd better have Avgas on hand every time you ad fuel to your tank - and be accurate with your measurements!

Read my comment above.....

Well if i really can't switch between pure regular gas and a mix of avgas 100ll and regular gas without adjusting the carb that's a problem because i can't always get that mix but i do not really want to risk engine damage also.
This would pretty much limit my range, more than an EV does.

At this point i dunno what i will be doing.

Run it.....but like mentioned above, you don't need to run 100% but even if you do, I doubt you'll have carb issues. I never did and lots of guys I knew weren't having issues either. After all, it's not alcohol. That stuff is another story all together.

Looking at the specific gravity of various racing fuels, it doesn't seem to matter whether they're listed as aviation fuel or race gas, the specific gravity is all in the same ballpark. Chevron supreme 91 is in the .73 range. VP Master Fuel Table | VP Racing Fuels

Yup!! And if the SG is so important, how come light aircraft doesn't run like crap on the ground....or even at 500 feet ALT?

Unless you have a pinging problem or you're racing and continually beating the **** out of it with redline RPM's all the time, just use the pump gas! I just drive my cars so I don't need hi-octane, as I have it tuned where it won't knock on pump gas. All the lead does is protect the seats during hi-RPM operation like racing.
To all the nay-sayers that say otherwise, why do most builders say you don't need hardened seats on a street car?

Used to run my 70 Challenger pretty hard in town and on the highway and never had any issues with it. Can't remember the exact mileage on it when I sold it but it was over 100k. I remember when everyone was going nuts because of the low/no lead issue. Chevy engines did have more problems with the no lead gas than Mopars though just because the cast iron in their garbage was low nickel! Fact! As a machinist I've cuts lots of high nickel cast iron vs low nickel and the sound the cutter makes is way different. One day I walked into a buddies shop and he was boring a block and it was really fairly quiet (in relation to a Mopar) and asked him what was he working on. He just laughed and said 'a Chevy'.

 

[Dave P]

Yup!! And if the SG is so important, how come light aircraft doesn't run like crap on the ground....or even at 500 feet ALT?

A couple of points...most piston engine aircraft have mixture controls.... pig rich to turning the fuel totally off.
EGT gauges to lean with and in some cases CHT also. Turbocharged engines even more "tuning" aids

Other than takeoff and landing I and most pilots I know like closer to 3000 feet between the airplane and the ground.....lots more choices if it quits making noise someday. And if actually going somewhere in non turbocharged I like maybe 7500-10000 feet depending on weather and terrain.

 

[RJRENTON]

So one guy says run straight av gas No problem. Except you need an electric pump.

another says any mix change requires a jet change Or it’ll run like crap.

Others say use 25%-33% av gas no problem.

the adjustment screws are for the idle feul mixture. wont do anything for cruising AF ratio.

Tell me again, why do I post on these threads?

better get: electric fuel pump, mini starter, mopar performance valve covers, ZDDP, EOS, Rotella, 4 wheel disc brakes, polygraphite bushings, 1.03 torsion bars, sway bars the size of your arm, amber high beam headlamps, amp meter bypass, headlamp relays, 120 amp alternator, Optima battery, pertronix, aluminum radiator with electric fans, green bearings, type F fluid, lobar kickdown cable, subframe connectors, green bearings, 3.55 “posi”, and the biggest BFG TA radials that will fit on the heaviest steel wheels ever made.

PS: don’t ever start the engine unless you remove the coil wire and crank it until you get oil pressure. Saves all the “engine wear” LMFAO

EXCELLENT SYNOPSIS.......but....you forgot to add: NGK spark plugs vs Champion vs AC vs Autolite vs E3 are best, manual transmission lubricant, DOT 5 vs DOT 3 brake fluid, best wax to use, best windshield wiper fluid, best beer to drink, nitrogen vs air in your tires, AND....whatever material and methodology I use is superior to what ever you do or use......just a casual observation.......
BOB RENTON

 

[Cranky]

EXCELLENT SYNOPSIS.......but....you forgot to add: NGK spark plugs vs Champion vs AC vs Autolite vs E3 are best, manual transmission lubricant, DOT 5 vs DOT 3 brake fluid, best wax to use, best windshield wiper fluid, best beer to drink, nitrogen vs air in your tires, AND....whatever material and methodology I use is superior to what ever you do or use......just a casual observation.......
BOB RENTON

It's easier to list the best of the worse beers to NOT drink!!

 

[Cranky]

A couple of points...most piston engine aircraft have mixture controls.... pig rich to turning the fuel totally off.
EGT gauges to lean with and in some cases CHT also. Turbocharged engines even more "tuning" aids

Other than takeoff and landing I and most pilots I know like closer to 3000 feet between the airplane and the ground.....lots more choices if it quits making noise someday. And if actually going somewhere in non turbocharged I like maybe 7500-10000 feet depending on weather and terrain.

Let's say you are at sea level on a 100 degree day with the humidity at 50% (I see that a lot here), so generally how high up off the ground do you get before your readings start changing enough to adjust the mix? I know the SG of avgas isn't all that much different than race fuel or pump gas for that matter. The main difference between avgas and pump gas is the lead content. The SG.....not so much.

 

[69a100]

Let's say you are at sea level on a 100 degree day with the humidity at 50% (I see that a lot here), so generally how high up off the ground do you get before your readings start changing enough to adjust the mix?

I'm guessin that SG means "specific gravity"?
If I remember right from my days of doing altitude chamber rides is that the atmospheric pressure is half at 17K than what it is at sea level. Now you throw in the pressure altitude, pressure gradient and other stuff, it changes the performance of the aircraft. Just like racers playing with the numbers at the track. I guess you'd have to look at the EGT and the EPR to know when to change mixtures? I'm not a pilot so I'm sure I'm not 100% correct on all this but I would guess things start to change around 10K feet or so depending on weather conditions. Hope it helps?
EGT= exhaust gas temps
EPR= engine to pressure ratio

 

[Photon440]

I don't think it really matters too much about aircraft engines at altitude, a lot of them never flew very high, keeping under 10,000 to avoid needing oxygen in unpressurized cabins. Planes like cropdusters stuck close to the earth most of their careers. One way or another, LL100 works pretty good in a car engine, if it needs it.

Meanwhile, the quest for getting all the lead out of avgas continues. Philips 66 for example is experimenting with manganese based additives instead of lead. But while the EPA and FAA have goals toward zero lead, the petrol companies may not want to invest too much into the solution. Avgas accounts for only about 1/10th of 1 percent of gasoline sales, so unless a cheap solution is arrived at, it may not happen.

 

[RJRENTON]

I'm guessin that SG means "specific gravity"?
If I remember right from my days of doing altitude chamber rides is that the atmospheric pressure is half at 17K than what it is at sea level. Now you throw in the pressure altitude, pressure gradient and other stuff, it changes the performance of the aircraft. Just like racers playing with the numbers at the track. I guess you'd have to look at the EGT and the EPR to know when to change mixtures? I'm not a pilot so I'm sure I'm not 100% correct on all this but I would guess things start to change around 10K feet or so depending on weather conditions. Hope it helps?
EGT= exhaust gas temps
EPR= engine to pressure ratio

As I remember, as the altitude changes (increases) the air density changes (gets "thiner"..less oxygen) and the temperature decreases, both of which require a leaner fuel mixture. In addition, carburetor air is preheated to prevent icing, as the altitude changes and density changes, the moisture in the air condenses (latent heat of vaporization) due to the vaporization of the fuel. Carburetor calibration becomes critical. EGT and EPR will show mixture distribution and utilization factors as an indication of the performance. This is the reason for "leaning" the mixture as altitude increases. Failure results an over rich mixture in fouled plugs and higher fuel consumption. Just my opinion of course......
BOB RENTON

 

[kiwigtx]

EXCELLENT SYNOPSIS.......but....you forgot to add: NGK spark plugs vs Champion vs AC vs Autolite vs E3 are best, manual transmission lubricant, DOT 5 vs DOT 3 brake fluid, best wax to use, best windshield wiper fluid, best beer to drink, nitrogen vs air in your tires, AND....whatever material and methodology I use is superior to what ever you do or use......just a casual observation.......
BOB RENTON

Silicone blinker fluid for the win.

Just my opinion of course.

Oh, and I'm thinking something else more appropriate for 'SG' in the vein of this thread.

 

[Dave P]

Let's say you are at sea level on a 100 degree day with the humidity at 50% (I see that a lot here), so generally how high up off the ground do you get before your readings start changing enough to adjust the mix? I know the SG of avgas isn't all that much different than race fuel or pump gas for that matter. The main difference between avgas and pump gas is the lead content. The SG.....not so much.

Actually if I was on a short runway on a 100 degree day I might do a full power runup and lean it a touch right on the ground.
Generally in temps of less than 90 degrees and at field elevations of sea level up to a couple of thousand feet I just leave it full rich on
climb out ( full power ) helps cool the engine. I'll lean it at any altitude once power gets pulled back to cruise levels.
Depending on engine instrumentation usually look at leanest cylinder's egt numbers then depending on engine manufactures recommendations, pilot's own personal thoughts yada yada will lean it some where between slightly rich of peak on some cases even lean of peak. There are a lot of variables.

 

[Photon440]

As I remember, as the altitude changes (increases) the air density changes (gets "thiner"..less oxygen) and the temperature decreases, both of which require a leaner fuel mixture. In addition, carburetor air is preheated to prevent icing, as the altitude changes and density changes, the moisture in the air condenses (latent heat of vaporization) due to the vaporization of the fuel. Carburetor calibration becomes critical. EGT and EPR will show mixture distribution and utilization factors as an indication of the performance. This is the reason for "leaning" the mixture as altitude increases. Failure results an over rich mixture in fouled plugs and higher fuel consumption. Just my opinion of course......
BOB RENTON

Another point to consider is that many aircraft engines, particularly in small private planes, are air cooled. For that reason, a lot of engines (example: Lycoming LO-360) state in the manual to use full rich for high power loads such as take off. It isn't the best setting for power, and isn't the best for engine life, but the extra fuel aids in carrying out excess engine heat. The cooler cylinder head helps prevent detonation. We don't have this issue with our liquid cooled engines.

 

[Cranky]

I don't think it really matters too much about aircraft engines at altitude, a lot of them never flew very high, keeping under 10,000 to avoid needing oxygen in unpressurized cabins. Planes like cropdusters stuck close to the earth most of their careers. One way or another, LL100 works pretty good in a car engine, if it needs it.

Meanwhile, the quest for getting all the lead out of avgas continues. Philips 66 for example is experimenting with manganese based additives instead of lead. But while the EPA and FAA have goals toward zero lead, the petrol companies may not want to invest too much into the solution. Avgas accounts for only about 1/10th of 1 percent of gasoline sales, so unless a cheap solution is arrived at, it may not happen.

I've flown in lots of small aircraft and have done some flying and have never ever gone over 5k feet in one. 15-2000 was more the norm and many times it was just above the heat dome. Here in the summer time, just above 1000 feet the temps get comfy especially in an open cockpit. It's also high enough to not get too friendly with radio towers.....

 

[mrhemi]

I've flown in lots of small aircraft and have done some flying and have never ever gone over 5k feet in one. 15-2000 was more the norm and many times it was just above the heat dome. Here in the summer time, just above 1000 feet the temps get comfy especially in an open cockpit. It's also high enough to not get too friendly with radio towers.....

Depends what you are doing. I used to fly a lot of cross country trips in my Piper Cherokee. The optimum efficiency altitude (by the flight manual) was 7000'. So we always tried for that density altitude (a whole other topic) for maximum efficiency on long trips

 

[PeteyDaMan]

ok, I'll throw my experience with 100LL in here
I buy it for my Charger with a 10.5:1 512 and a 950 carb
The engine loves it. I typically run it straight.
It does not run leaner, if anything it runs fatter. AFR gauge shows it went from 12.5:1 to about 11.5:1 at cruise
I had gotten a bad batch of 93 at a local gas station so I drained and and bought the 100LL just to prove I had bad gas
Once I did that I loved how the car ran so I continue to run it although I put only a few miles a week on the car

let the flaming begin (or continue....what ever)

 

[Mally69]

ok, I'll throw my experience with 100LL in here
I buy it for my Charger with a 10.5:1 512 and a 950 carb
The engine loves it. I typically run it straight.
It does not run leaner, if anything it runs fatter. AFR gauge shows it went from 12.5:1 to about 11.5:1 at cruise
I had gotten a bad batch of 93 at a local gas station so I drained and and bought the 100LL just to prove I had bad gas
Once I did that I loved how the car ran so I continue to run it although I put only a few miles a week on the car

let the flaming begin (or continue....what ever)

I ran it in my car for years, straight. Not mixed. Tuned my engine on it. It runs just fine. It burns slower and colder than 93 obviously so if u have lower compression ur total timing may be need to be a tad more advanced than normal with it. My dist was locked out so i could clearly tell where it wanted to run..

 

[Jerry Hall]

My cars love it too, but it's up to $7 per gallon here now, so I mix it 50/50 with 90 octane non ethanol to lower my fuel costs. Just saying.

 

[66Satellite47]

Back in the day, mid '70's I mixed 100LL with the premium available with 12.3 CR. It worked great. With todays non oxy, I'm sure 100LL 50/50 would work fine with iron heads and 10.5 to 11 CR.

 

[biomedtechguy]

The car is currently tuned for standard 95 Octane (german rating standard) gasoline that i can buy at every pump. At least that's what im putting in and the engine runs great.

I read every post but I don't understand the OP question maybe?
As far as LowLead (the LL in AVGas), how is some lead worse than NO lead (unleaded) pump gas for non-hardened valve seats when lead acts as a valve seat cushion? I'd think it would be better.
Tuning advantage since you state the engine runs great on pump gas?? You should be able to get more timing advance, but that's only an advantage if your engine needs more advance or makes noticeably more power with more advance at WOT.

 

[33 IMP]

I read every post but I don't understand the OP question maybe?
As far as LowLead (the LL in AVGas), how is some lead worse than NO lead (unleaded) pump gas for non-hardened valve seats when lead acts as a valve seat cushion? I'd think it would be better.
Tuning advantage since you state the engine runs great on pump gas?? You should be able to get more timing advance, but that's only an advantage if your engine needs more advance or makes noticeably more power with more advance at WOT.

I may be misinterpreting the OP, but I think he's saying his car runs fine on his 95 (probably the same as our 91, just rated differently) but he's worried about the valves and seats, from unleaded fuel.
We basically told him that a gallon or two 100LL in a tank is plenty to save his valves, IF he can get it.
I personally run around 33% avgas, because my combo is on the ragged edge of running on pump (it will, if I take a couple degrees out), and I CAN get it.
(and Arizona avgas is cheaper than california 91 !).