Can i run 100% AVGAS 100LL?

[Michael_]

Since england isn't part of the EU anymore i can't import lead additiv (not substitute) anymore.
But my 1969 Dodge Charger R/T 440 has no hardened valve seats (engine has never been rebuilt) and i'm not planning on upgrading to hardened valve seats anytime soon.

It might not be absolutely necessary

Will Unleaded Gas Burn up the Exhaust Valves in an Old-School Muscle-Car Engine?

Does your engine really need hardened valve seats? Will Unleaded Gas Burn up the Exhaust Valves in an Old-School Muscle-Car Engine?

www.motortrend.com

but i tend to be a performance oriented driver.

I can get AVGAS 100LL at my local airport. (I asked, they will sell it to me.)
So i think about switching between filling it up at the airport and regular gas stations. (To maintain some lead in the system.)

Question is can i run 100% pure AVGAS 100LL and can i switch between this stuff and regular 95 Octane gasoline without adjusting the ignition/carb?
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.

Or do i have to settle for one specific type of gas because of the different octane rating?

It would kinda suck having to mix different types of gasoline.
Edit: Even problematic on longer trips since this car likes to drink gas.

 

[33 IMP]

I get 100LL at my local airport, too. I run somewhere around a 60/40 mix, with our pump premium, 91 the way its rated in the US. (60%pp)
If yours runs good on your 95 (don't have to back the timing off) a couple gallons of LL should be plenty, per tank.
Mine is a 10.5 (honest, not mopars mythical c.r.) iron head 500hp 440.

 

[R413]

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

 

[Rusty knuckles]

I dunno about specific tuning to the fuel as I don't change fuel a lot but otherwise yes you can run it straight. I currently have it in my 71 charger. My only suggestion is make sure you have an electric fuel pump or a really good battery or carry a priming bottle with you. The gas in the system evaporates quickly and you have to get it pumped back up every time you shut down.

 

[Michael_]

Thanks!

I run somewhere around a 60/40 mix

What percentage is pump and what avgas?
Is 50:50 already to much avgas?

Under this circumstances i think i have to put a mix of avgas and regular gas whenever i start/end my trips and in between pure regular pump gas.
Might carry a canister with avgas and pour it in at the first tank stop of each trip. (That's a couple gallons)

I would have loved to avoid mixing different types of gasoline (to keep it simple) but seems like i have to.

Edit:

I dunno about specific tuning to the fuel as I don't change fuel a lot but otherwise yes you can run it straight. I currently have it in my 71 charger. My only suggestion is make sure you have an electric fuel pump or a really good battery or carry a priming bottle with you. The gas in the system evaporates quickly and you have to get it pumped back up every time you shut down.

Interesting. Well i do not want to convert to an electric fuel pump, especially since it's a nice original car and i dunno about pouring gas in the barrels everytime.
It probably isn't enough to pump the gas pedal like 20 times?
Extended cranking (which i think you refer to when saying a good battery) is probably hard (at least) on the starter?

 

[sam dupont]

I used to get a deal at a fuel terminal. Through that pipe, they would pump a few different octanes of AV gas. The purges between products would mix the tank I pumped from. They estimated the tank was at 103.

I burned it in a high compression 2500 in a stripped down TR6. I guess I was young, dumb, and lucky as I burned a lot of it autocrossing. Being a LBC in the North, it sat a lot, but the gas never went stinky. Somebody bought the motor out of it and I went V8, so if I hurt it, I never knew and they never said anything.

 

[dadsbee]

I run all of mine 33/66.. 5 gallons Av to 10 gallons premium. All run great...and smell nice tooooo

 

[Rusty knuckles]

I haven't found pumping the pedal to work as there simply isn't any fuel available to get squirted down the intake. I use avgas more for the stability it has than the octane or lead. Everything has trade-offs I suppose. But I'll bet you can hide an electric pump really well and not compromise originality. I hung the pump on my 69 above the rear axle in an existing hole. Other than the hum it makes before it starts you'd never know it was there. Cures all vapor lock issues too.

 

[440 PHIXX]

I ran 50/50 in the 80’s in my ‘Cuda 440-6. But... I have been daily driving a slightly warmed ‘68 273 in my wagon, and the stock 383 in my 4 door. And while I haven’t had the 383 apart, I did pull the heads on the 273. I didn’t see any exhaust valve recession into the head. Has anyone else seen any appreciable wear?

 

[33 IMP]

@Michael _ I run approximately 60% pump premium. 1 to 2 like dadsbee uses works fine too. 8 gallon fuel cell, about five gallons pump premium, then top off with avgas. I have found no need for a jet change for the avgas.

 

[Michael_]

I think the tank capacity is about 60 Liter?
In this case i could carry a 20 Liter canister with AVGAS 100LL for a 1/3rd AVGAS : 2/3rd Regular pump gas mix.

If i need more gas i will run 100% pump gas in between.

That's probably what i do.

 

[gkent]

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!

Personally, I wouldn't worry about the seats. I asked this same question years ago and was told "you might see some wear after 25,000 miles".

 

[gkent]

I run all of mine 33/66.. 5 gallons Av to 10 gallons premium. All run great...and smell nice tooooo

Do you really need avgas with premium ?!?!

 

[Michael_]

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!

Personally, I wouldn't worry about the seats. I asked this same question years ago and was told "you might see some wear after 25,000 miles".

Do other users have the same experience?

When you say "tweak the carbs" do you mean playing with the adjustment screws or putting in different jets and stuff?

 

[dadsbee]

Do you really need avgas with premium ?!?!

500 gallons of it in the yard and at least 3 of 5 cars without hardened seats and high compression... no point gambling.

 

[Michael_]

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.

 

[kiwigtx]

You have been warned! LOL

 

[Michael_]

View attachment 1315582

This is not the engine but the governments fault for banning leaded gasoline.

 

[R413]

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

 

[kiwigtx]

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

Still waiting for the muffler bearings to collapse. Common fault with R/T Chargers.