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Author Topic: Aviation Gas Question
Randy Thieme
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Searched the forum on "av-gas" and did not get any hits so I'll post the question. (I might have gotten the abbreviation wrong.)

Where I work a number of my co-workers are private pilots and fly recreationally. I've been asked twice now why I don't use 100 octane aviation gas (av-gas). Don't know! [help] So I'll pass the question on - why not av-gas? I'm going to get asked the question again by a co-worker so I want an intelligent answer instead of running my finger up and down my lips going bb-bb-bb-bb-bb.

d mathias Verified Driver Made Donation to Website
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Legal compression ratio/max timing advance does not warrent the use of high-octane fuel. Octane only prevents detonation, it does not increase HP.

Also, "What, am I suppose to run to the airport everytime I gas-up?"

Mike Colangelo Verified Driver Made Donation to Website
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Randy, you must be referring to 100LL (100 octane low lead avgas), aka "blue gas".

I've heard of drag racers with high compression engines using 100LL but never any road racers.

Two down sides to using this fuel in your SM are:
1. lead fouling of the spark plugs
2. if your car still has a catalytic converter, the lead in the gas will destroy it.

Also, there might be legality issues with using this fuel in a car that is street-driven (as some SMs are). I think this has to do with the fact that the price of avgas doesn't include road taxes or something like that.

And I'm pretty sure that avgas wouldn't fall under the spirit of POG. [Wink]

Tom's Double O Verified Driver
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Also bad for the oxygen sensor. Not a problem for WOT but might cause rough running in lower RPMs.

-Tom

wheel Verified Driver Made Donation to Website
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I have run 100LL for years in the ASedan. The most consistent fuel you can buy. Never any issues, although carb needs to be re-jetted, when changing from 110 Sunoco. As was pointed out, it does contain some lead. Not really needed for SM.

EBudman Verified Driver
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We ran it in the FVs as well. I got out about the time that the cheater fuels started showing up. Not the greatest for HP, but we used it for the consistancy that wheel mentioned.

Absolutely no advantage to using it compared to POG.

Bellwilliam Verified Driver
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why is it no advantage ? with the octane, doesn't all the ECU-modded car (and isn't that every top SM?) can take full advantage of it ?

fishguyaz
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I run av gas in my formula ford. its about $4/gal compared to the stuff they sell trackside which goes for $8+/gal

+1 to all of the above comments as to why you dont want it in a SM.
in my SM i use pump gas with 91 octane, it works well.

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Josh Pitt
AZ Region

EBudman Verified Driver
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quote:
Originally posted by Bellwilliam:
why is it no advantage ? with the octane, doesn't all the ECU-modded car (and isn't that every top SM?) can take full advantage of it ?

Octane does not make HP in any way, shape or form... without elevated compression, it actually burns too slow & makes marginally LESS HP. Octane merely allows you to run more compression without having to reduce ignition advance to control spark knock. Running more compression, in the amount requiring more than 87-89 octane is not really an option in our "spec" class.

TillerTech
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Years ago, av gas was formulated for low compression and low speed motors. The octane rating was a different formula than the automobile fuel. Most aircraft motors turn less than 4500 rpm. If you look at the application, the common aircraft motor makes .5 hp per cubic inch displacement. Continental O-200 = 100 hp. Compare that to the 1.6 ltr Miata, 97 cubes and 125ish HP. My "F" motor puts 140 to the ground in a mild tune, but will not crank over to start with 91 in the tank.

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Jamie Tucker Series Champ

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Most piston aircraft engines (Lycoming, Continental) do not go over 3000 rpm. They are also very low compression (under 80 PSI). The 100L formula was invented during World War 2 to help control knock at high altitudes in supercharged aircraft. Later it became 100ll as the full leaded fuel went away but it is still used for the same reasons in GA aircraft. The other benefit is 100LL does not go bad like regular gas.

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38BFAST Verified Driver
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It may be called Low Lead but there is considerable lead in the fuel. When doing my annual on my plane a lot of time is spent cleaning the plugs from lead deposits. Lead will kill a O2 sensor in short order.

--------------------
Ralph Provitz
#38
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Higher octane fuel can produce more HP. Gases like Sunoco GT use alcohol to raise the octane rating. Added alcohol can help to lean the mixture, which will help to produce more HP. Although too much alcohol will reduce the HP because it has a lower combustion energy content.

--------------------
Jeff Thompson
SM #16 - Detroit Region
Great Lake Division

Randy Thieme
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Thanks for all the input!

Shop Teacher
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I rarely drive my car at 15000 ft. Av gas is make for altitude. Not sea level.

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Al Angulo
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Kent Carter Verified Driver Made Donation to Website
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I have always heard that the vapor pressure issue (sea level vs 15k') with avgas, but wondered it is still applies with injected cars. Thoughts?

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Do I turn my 99 Hard S into a killerfast SM or seek a donor?

Mike Colangelo Verified Driver Made Donation to Website
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quote:
Originally posted by Shop Teacher:
I rarely drive my car at 15000 ft. Av gas is make for altitude. Not sea level.

???

Back when I was flying Cessnas and Pipers (I can only afford one expensive hobby at a time) I rarely flew above 6500 ft MSL. Those engines seemed to run just fine at any altitude I flew.

Michael53
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As mentioned, the only real problem is the lead. Currently available 100LL has 2 grams of TEL per U.S. gallon of fuel. That's enough lead to take out an O2 sensor before the end of the first practice session. Other than the check engine light coming on you'd never notice it. SM's are almost always in open loop mode. But, I'll stick to POG in my spec Miata.

Where I love to use 100LL (other than my plane of course) is any occasional use device: Chainsaw, edger, mower/tractor near end of season. The shelf life of 100LL and never having to deal with a gummed up carburetor more than offsets the price delta with auto gas. I always keep a 5 gal jug at the house!

Weekend Warrior Verified Driver Made Donation to Website
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quote:
Originally posted by Michael53:
As mentioned, the only real problem is the lead. Currently available 100LL has 2 grams of TEL per U.S. gallon of fuel. That's enough lead to take out an O2 sensor before the end of the first practice session. Other than the check engine light coming on you'd never notice it. SM's are almost always in open loop mode. But, I'll stick to POG in my spec Miata.

Where I love to use 100LL (other than my plane of course) is any occasional use device: Chainsaw, edger, mower/tractor near end of season. The shelf life of 100LL and never having to deal with a gummed up carburetor more than offsets the price delta with auto gas. I always keep a 5 gal jug at the house!

How wide is your street? I'm landing there next time I'm low......

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Michael53
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Alan,
The street is a little narrow. Most of my visitors prefer to land on the 60' wide 2600' strip on the other side of the house! (grin) [thumbsup] - Mike

Weekend Warrior Verified Driver Made Donation to Website
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That would be a bit less stressful..

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TillerTech
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I'll be landing on the Polish runway, 2800' wide and 150' long...........

There are much better things to chase than bad gas.

John

--------------------
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Danny Steyn Verified Driver
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quote:
Originally posted by TillerTech:
I'll be landing on the Polish runway, 2800' wide and 150' long...........
John

now that's funny!

--------------------
Danny
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wheel Verified Driver Made Donation to Website
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I did get in trouble with the Stewards because I landed counter race on the front straight at MAM. Photo at left.

Reggie Verified Driver
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Stewards can sometimes be SO darn picky over the little things....

UCFBrett
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Once when I had to fill up at Auto Club Speedway, they had run out of 91 octane. I had to pump in some 100 octane, which made no discernible difference in performance. Sure smells cool, though.

Now that I think about it, I did have to replace the O2 sensor not long after that.

J. Douglas
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I don't know if this applys to Miatas but back in the Spec XR100 days we used to ecourage new rookies to use race gas because it burned slower in our stock motors. Regular gas actully burned with more of a "pop" and they seemed to run off the corners better. One of the secrects you used when you need to win so you had gas money to get home.
Speaking of semi cheating I used to fill the air cleaner up with starting fluid so when you started off the line with a dead motor it would make great power for the first ten yards. Enough to give you the holeshot.... and the money.
Jerry

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Just before you go out to qualify, drop a few chunks of dry ice in the gas tank. It will keep the whole tank of fuel nice and cool.

Randy Thieme
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quote:
Originally posted by wheel:
Just before you go out to qualify, drop a few chunks of dry ice in the gas tank. It will keep the whole tank of fuel nice and cool.

Frozen greenhouse gases? That is sooooo environmentally wrong. I'm calling the White House. [Smile]

   

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