[Question] Av gas
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Av gas

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    Senior Member Luckie Stiff's Avatar
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    Default Av gas

    What are the pros & cons of running it in your boat?

    Are there any changes that need to be made?

    Thanks
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    "Don't you realize that there are already enough people in the world to hate without you putting in so much effort to give me another?"

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    Senior Member jockorace's Avatar
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    Skip,
    If there is an easy, close location to fill up your boat with LL100 Av-Gas, I would run it. It's reasonably priced compared to 108 (or higher) and unless you are running some crazy high boost levels to require more than 100 octane, Av-Gas is one of the best fuels for the $$. E-85 is actually a better"bang for the buck", but that's another thread. I find it amusing when I see a guy paying $10.00 + for C12/C16 race gas and their engine really doesn't require it.
    I ran LL100 for over 20 years in my blown deals. Simple formula 1) Jet up approx 4 jet sizes (never ran power valves) 2) Run a top end lubricant (Marvel Mystery Oil).
    Av-Gas is a very 'consistant' fuel in regards to quality, obviously since it's for airplanes. If for no other reason.......it smells great! Jocko

    P.S. Another option is to mix it 50-50 with pump gas (premium) to achieve approx 96 octane. Union 76 in Lakeport used to sell that mix right on the water. They marketed it as "Sports Gas".

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    Quote Originally Posted by jockorace View Post

    I ran LL100 for over 20 years in my blown deals. Simple formula 1) Jet up approx 4 jet sizes (never ran power valves) 2) Run a top end lubricant (Marvel Mystery Oil).
    Av-Gas is a very 'consistant' fuel in regards to quality, obviously since it's for airplanes. If for no other reason.......it smells great! Jocko

    P.S. Another option is to mix it 50-50 with pump gas (premium) to achieve approx 96 octane. Union 76 in Lakeport used to sell that mix right on the water. They marketed it as "Sports Gas".

    I mixed it 2:1 for years ( 10 gal av gas/ 5 gal 91)

    I'm planning on running it in the 565 again ( 13:1 comp) ........when I ever get on the water again.

    S CP

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    "BEER BUDGET RACING" Bodean's Hammer's Avatar
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    Quote Originally Posted by Sleeper CP View Post
    I mixed it 2:1 for years ( 10 gal av gas/ 5 gal 91)

    I'm planning on running it in the 565 again ( 13:1 comp) ........when I ever get on the water again.

    S CP
    I have heard from people that mixing it "helps" the burn?? and that it will actually make more power mixed 50/50. I run it straight on a 13:1 motor.

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    Head Janitor FormulaZR's Avatar
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    Potential cons:
    Can make reading plugs a little harder
    Will foul O2 sensors
    If you don't need high octane it's a waste of money

    Pros:
    Cheaper than race gas
    Dead consistent
    Pretty blue tint
    Doesn't have the additives of Mogas - stays fresh much longer
    Airport fuel stations make filling a dual tank boat an absolute breeze
    Doesn't have that terrible smell


    "No, my boat doesn't need any more power" - No one ever

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    Senior Member SoldHondaBoughtHondo's Avatar
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    Quote Originally Posted by Bodean's Hammer View Post
    I have heard from people that mixing it "helps" the burn?? and that it will actually make more power mixed 50/50. I run it straight on a 13:1 motor.
    That seems to be true on some motors...while i don't know for sure on anything other that the stuff i have tinkered with

    I did have a 1000 cc air cool bike that lost 2-3 mph on the top end on straight av green....put pump gas back in and it was still down on power.
    ( had a clean stretch of I-80 that i ran on the way to work every day...I liked leaving late for work and still get there early)

    I ran about 4 gal. of pump through it...2 days later i got my number back...So i added about 50% av..picked up almost 2. Next day i ran close to 100% av and lost 4 mph....

    I changed nothing else... Bike was always consistent...125-130 on a bike with no faring is very hp sensitive.

    5 hp is worth about 2mph at that speed...
    10.0-1 compression..It did respond to timing changes with the av.
    36 total is stock to 38 total was good for almost 3 mph...past 40*it nosed over.

    We used to have a 550 gal. above ground av green tank where i worked..had an old 70 camaro with a 10.5-1 327 with z28 off road cam and z28 chambered exhaust. Ran ok on pump gas...i could back it up to av gas tank and add... if i was low on pump you could hear it when it hit the motor..cam sounded better...idle rpm came up 50-75 rpm...and make ya like to sniff tailpipe!...av and a little timing on that deal was the difference between 147 and 153....flat ground air density =" 60 fwy east of central about 3 am" ....ya, i know..not very accurate....lol....but it was repeatable..

    As for how any of that applies to marine....i have no idea....it might be as simple as tune to suit application...but on a 13:1 deal
    i would think it would like 100%
    I don't have much run time yet but my 11:1 closed chamber deal seems ok with 89-91 mix @ 32* and the one time i had 50% av 91 mix it was pulling the best rpm at the hit around 38*.

    I was always told av burns a little slower but hotter..more timing covers the burn time and a slightly colder plug controls the heat.
    Never did much with jetting....mmo is a good thing...

    A load of av green, a splash of mmo and 30-1 bean oil in an 84 495 ktm is a thing of beauty...Back to back to back passes up big sand mountain with the throttle pinned...ran the same mahle for 12+ years.....although my buddy...who builds engines...refuses to run av in anything...

    My thoughts are kinda simple....change things, change one thing at a time...pay attention to everything and take nothing for granted......and if someone tells ya your up in the night, always listen....cause 'told ya so' can really suck
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    Senior Member jockorace's Avatar
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    SHBH, interesting post. It sounds like you had positive results on several applications. I'm surprised though that you didn't melt something down given that you never upped your jetting (even slightly). Either you were initially jetted a little fat, or you just got lucky. Just think how much speed you would have gained with more jet!
    On my blown deals w/2 dominators I absolutely had to go from 90/94 up to 94/100 jetting. Jocko
    Last edited by jockorace; 08-23-2011 at 03:22 PM.

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    Quote Originally Posted by jockorace View Post
    SHBH, interesting post. It sounds like you had positive results on several applications. I'm surprised though that you didn't melt something down given that you never upped your jetting (even slightly). Either you were initially jetted a little fat, or you just got lucky. Just think how much speed you would have gained with more jet!
    On my blown deals w/2 dominators I absolutely had to go from 90/94 up to 94/100 jetting. Jocko
    10.8:1 compression 565 @ 855 hp on Trick 104 made 850 hp with 3:1 av gas/ 91 mixture same jetting same timing, same dyno, same day, same hour on the clock.


    S CP
    Last edited by Sleeper CP; 08-23-2011 at 04:52 PM.

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    One of the big "pro's" for me is NOT paying sales tax for av. It really pisses me off to pay Tax on gas that you don't use to run on a public hwy or street. Especially if you buy your gas at a dock were they jack the price up to begin with!

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    Member jonesdrivingajones's Avatar
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    Default remember

    Just remember, as all the pros or cons are stated, av gas is formulated to be used at higher elevation. I agree, it is a cheaper source, but if you're at the level of av gas vs. barrel gas; then you have spent enuff on your engine to not worry about cost of fuel.
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    I have to disagree about AV gas being formulated to run at higher altitude. AV gas is used from below sea level to higher altitude. You may even buy the gas below sea level and fly to a mountain top and it needs to work. Jetting will change with altitude though. The major difference is AV gas is a dry gas from the airport. That means it doesn't have water in it. Water in an airplane's fuel can be a problem since the water would freeze at altitude. Airports are very careful about keeping water out of what you get.

    I ran it for years before going to E85 and never had a problem. I have never used a lubricant in my AV gas, but I know many that do. I could still never find any damage caused by fuel.

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    Senior Member Luckie Stiff's Avatar
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    Thanks for all the replies guys. It's not that I'm at a point where it's AV or barrel gas, but I am @ the point that 93 octane is my only real option. Doing some comparison pricing this past weekend and it didn't seem to me to be too high, about $1.75 difference. I think I'll go 50/50 this weekend and see what the boat thinks about it...
    "Don't you realize that there are already enough people in the world to hate without you putting in so much effort to give me another?"

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    Member TOMSS1's Avatar
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    Quote Originally Posted by jockorace View Post
    SHBH, interesting post. It sounds like you had positive results on several applications. I'm surprised though that you didn't melt something down given that you never upped your jetting (even slightly). Either you were initially jetted a little fat, or you just got lucky. Just think how much speed you would have gained with more jet!
    On my blown deals w/2 dominators I absolutely had to go from 90/94 up to 94/100 jetting. Jocko
    Jocko is 100% correct. Blown 509, 2 Pro systems carbs, Intial dyno beak in and runs w 110 race gas on Saturday, A/F looked fine as the carbs came out of the box, Finshed up today, Timing ended up at 34, used 100 Low lead blue AV gas for all pulls today. Jetting had to go up 7 numbers to get the A/F back to a level we were comforable with. Specific gravity of the fuel is low (6.8) vs 110 race gas. Seemed like a good deal for a mild deal at about 950 hp. My Dyno guy doesnt love the idea but A/F ended up OK and the EGT numbers were fine. Time will tell.

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    Quote Originally Posted by TOMSS1 View Post
    Jocko is 100% correct. Blown 509, 2 Pro systems carbs, Intial dyno beak in and runs w 110 race gas on Saturday, A/F looked fine as the carbs came out of the box, Finshed up today, Timing ended up at 34, used 100 Low lead blue AV gas for all pulls today. Jetting had to go up 7 numbers to get the A/F back to a level we were comforable with. Specific gravity of the fuel is low (6.8) vs 110 race gas. Seemed like a good deal for a mild deal at about 950 hp. My Dyno guy doesnt love the idea but A/F ended up OK and the EGT numbers were fine. Time will tell.
    And what were the numbers between the two fuels ? The 565 was down 5hp, but I didn't re-jet or change the timing.


    S CP

    "Dark Sarcasm"
    Going fast is only half the fun ... what you make go
    fast is the other half.
    " A Government big enough to give you everything you want is big enough to take away everything you have"

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