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100LL AV gas

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Hello, I was wondering if 100LL AV gas can be run in a CRF 450? Thank you!

Edited by CCC4

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yes, Avgas just does not have all the detergents and ethenol blend pump gas does. It is regulated by the faa and government. Its just better gas. If your crf is modded then you might need higher octane than 100LL avgas.

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I read once that avgas was formulated for a slower burn rate than auto gas. Aviation reciprocating engines are usually run in the range of 1900 to 2500 rpms, for your crf thats just above idle, so you may not be getting as much power as you would with car gas since the fuel air charge might still be burning when the exhaust valve opens. This would translate to reduced fuel economy since you would be using higher throttle settings to achieve the same power you would with car gas.

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The AV gas will avoid detonation better than pump gas. But that doesn't mean you'll make more power with it either though.

If you were to put a sniffer on the pipe while running AV gas you'd find a ton of HC's in the exhaust. Thats unburned fuel. That unburned fuel carries a lot of heat out of the combustion chamber which will lower temps. Which helps again with detonation.

Two stroke guys seem to have decent luck running it. You can "get away with" more stuff on Av gas without having to deal with catastrophic detonation, like high compression and short duration cam combo's. But any real gain will be in your head, not at the tire.

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i run 110 leaded, it makes a difference on how the engine performs. i don't think it makes more power, it just works better than pump gas. problem is it costs double+.

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I run nothing but 100LL in my 2-strokes so I always have some around. Because it's already in my garage, there are many times that I fill my CRF's tank up with 100LL. There is no noticeable difference in power or throttle response between 100LL and premium pump gas in a CRF450, but the lead in the 100LL may improve intake valve life. It's good fuel and it's the cheapest fuel I can get in Texas that doesn't contain Ethanol. At $4.30/gal 100LL is only 70 cents more than premium pump around here.

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I read once that avgas was formulated for a slower burn rate than auto gas. Aviation reciprocating engines are usually run in the range of 1900 to 2500 rpms, for your crf thats just above idle, so you may not be getting as much power as you would with car gas since the fuel air charge might still be burning when the exhaust valve opens. This would translate to reduced fuel economy since you would be using higher throttle settings to achieve the same power you would with car gas.

....also formulated for running at altitude (lower oxygen), and for running the motor at constant or steady RPM for extended timeframe.

Unfortunately, I don't have the mojo to hold my bike wide open for the length of a race! :smirk:

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....also formulated for running at altitude (lower oxygen), and for running the motor at constant or steady RPM for extended timeframe.

People express that theory all the time, but in reality, 100LL runs like pump gas. The benefits of 100LL are more consistent jetting, cleaner top ends, no gunked up carb from ethanol, less prone to detonate, longer storage life and possibly longer valve life.

100LL is good fuel for dirt bikes.

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People express that theory all the time, but in reality, 100LL runs like pump gas. The benefits of 100LL are more consistent jetting, cleaner top ends, no gunked up carb from ethanol, less prone to detonate, longer storage life and possibly longer valve life.

100LL is good fuel for dirt bikes.

I agree. But for me (and maybe not for everyone else), I have to go right by the station that sells no-ethanol fuel to get to the airport. So I get all the benefits mentioned here, and the AVgas costs more.:smirk:

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Av gas is designed for low-rpm and low-compression motors. FMF and Pro-Circuit would send letters back with their motors saying "DO NOT RUN AV GAS".

I never tried AV gas but I figured the guys that build motors for a living know they are talking about. MXA and Dirt Bike also said not to use AV gas.

I do know you want to avoid ethanol! It's just plain bad for everything.

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I agree. But for me (and maybe not for everyone else), I have to go right by the station that sells no-ethanol fuel to get to the airport. So I get all the benefits mentioned here, and the AVgas costs more.:smirk:

Yeah, Florida doesn't have the EPA air restrictions that most us us deal with so you guys still have good pump gas.

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Av gas is designed for low-rpm and low-compression motors. FMF and Pro-Circuit would send letters back with their motors saying "DO NOT RUN AV GAS".

I never tried AV gas but I figured the guys that build motors for a living know they are talking about. MXA and Dirt Bike also said not to use AV gas.

I do know you want to avoid ethanol! It's just plain bad for everything.

The reason that PC and FMF would do that is because their full mod 2-stroke engines require 110 octane so you need something like C12.

If you want a fuel that's better than pump gas, 100LL is a good option. I've been using it since 1981 in my dirt bikes and I've never suffered any ill effect from it. I haven't had a single engine failure since 1980 so the fuel is good.

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Hey thanks! Yes, I run 100LL in my YZ 290 smoker with excellent results. A buddy of mine told me that I would be fine with 100LL in a 4 stroke but he also suggested mixing a little pre-mix, somewhere around 100:1? Would this just be kind of an insurance? I was also thinking about running it in a 280 4 stroke with FMF full exhaust with power bomb header. Any real benefits? I can buy 100LL for $4.88 a gallon. Thank you for all the feedback! :smirk:

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Any real benefits? I can buy 100LL for $4.88 a gallon. Thank you for all the feedback! :smirk:

There are real benefits with a 2-stroke because many stock and mildly modified 2T engines detonate on pump gas. 100LL is perfect for them.

Stock 4-strokes tend to run well on ethanol pump gas, but if you want to avoid the problems associated with ethanol, 100LL is a good alternative. I never add oil to 100LL when I use it in my thumpers.

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Another thing to consider is the lower energy content of ethanol (84,600 BTU/gallon). It is less than premium gasoline

(131,200 BTU/gallon), so using the typical E10, 90% gasoline and 10% ethanol (120,900 BTU/gallon), will produce slightly less power across the board. Also, fuel economy will suffer.

(fyi - A BTU is a "British Thermal Unit" and is the amount of energy rquired to raise the temperature of 1 pound of water 1 degree F.)

Datasource: Transportation Energy Data Book from Oak Ridge National Laboratory http://cta.ornl.gov/data/appendix_b.shtml.

Hope this helps!

Edited by jleblanc321
typo & updated information

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Av gas is designed for low-rpm and low-compression motors. FMF and Pro-Circuit would send letters back with their motors saying "DO NOT RUN AV GAS".

I never tried AV gas but I figured the guys that build motors for a living know they are talking about. MXA and Dirt Bike also said not to use AV gas.

I do know you want to avoid ethanol! It's just plain bad for everything.

Its not just the octane, they also want more lead in the fuel. The lead is slippery stuff and helps the bottom ends live longer. More oil doesnt always to it either.

Things to note this would be the massive problems with the 500 two strokes in MotoGP when they took away the lead. Every factory had riders going over the bars at close to 200mph when the engines seized up at WOT.

In Dirtbikes we dont generally have those kinds of problems, but it illustrates the issues.

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Have used AV gas since the mid 70's run it in my 13.5 to 1 CRF 450 no problems!

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i think try VP C12 race fuel at about 20 % mixed with premium gas you guys will never go back 2 avgas .theirs also a oxygenated vp fuel desined for 4 strokes U4 i think is the name of it but i have not tryed it yet

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With oxygenated fuel you can run a bit richer on the main and it feels smoother on power delivery IMO.

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