Straight av gas in 800cfi?

[BILTIT]

Anyone running straight av gas in the cfi-2 800's for lengths of time?

Have a 13.6 par head on my long rod and running ~25% race fuel mix at 1800ft with no DET. Brad says he can make me a 14.5 head, I figure I would need almost a 50/50 of race or go straight av. Not sure if straight av has any bad sides with this motor/fuel system?


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[JonezyBones]

Guys with turbo's do all the time. They mix oil with their fuel to help keep the fuel system lubricated.

 

[damx]

Did you gain anything from the 12.5:1 head.

 

[BILTIT]

Yup, 250rpm. Added 2grams of weight and still running 8250rpm (69.5g at 1850-2200ft, maxed out my adjustables). Much more responsive as well.


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[Jaynelson]

The only thing that comes up in the sled world is people claiming its a "dry" fuel. I think the whole "dry" thing was made up by the sled world. No one in the turbo car world ever brings it up, as it is inaccurate. If anything, it has more lubrication than 91 because the lead is a lubricant.

 

[machinest660]

I was running 50/50 av gas premium on my pro with the MTNK fix kit and 13-1 head, The sled just didn't seem as responsive and sometime had a stumble in it as compared to 25/75 blend of race gas. It for some reason still kicked into DET limp mode on the av gas well, It just seemed to run better on the race gas for some reason. Thats just my experience with av gas any way. If i keep this sled next season I will be going to a lower compression head just so i can run pump gas. Let us know what you decide and how it works.

 

[BILTIT]

I may try some av gas with this setup and compare the different fuels.


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[Ultrasauras]

av gas

I may try some av gas with this setup and compare the different fuels.


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I run a 13.6-1 pa head and a MTNTK fix kit at 3400 feet i run 70/ 30 avgas and 50/50 in the mountains sled works good running 11-66 at 6-8000 feet with all other clutching stock on my 2012.

 

[BILTIT]

I was running 62g from 6-8000 with the 12.5 domes, guessing if i gained 2+gram here at home i should gain 2+grams in the mountains aswell so 64+g (these are dalton adjustables so more like the polaris 10 series weights). I use stock primary spring and have a TIED secondary which i switched out back to back with carls cycle clutching setup.

 

[assault11]

Guys with turbo's do all the time. They mix oil with their fuel to help keep the fuel system lubricated.

Av gas and race gas lubricate more with the lead. Av gas and race gas do eat at the fuel filters though so you should change them twice as often. Some people love av gas some people hate it. I would just stick with that race gas. IMO av gas isn't good for these high heat high rev 2 stroke motors. Av gas was made for planes which aren't ever really stressed and only rev around 3000 rpm not 8000 and pinned for 30 seconds at a time. You'll make more power with a race/ premium blend and have lower chance of det

 

[3beans]

The lead may foul plugs a bit faster to!

 

[mountainhorse]

So that we are talking "apples to apples" here... Using Motor Octane Numbers (MON)

100LL AV gas approx 104 MON
"110" Race Gas approx 106/107 MON
Pump Premium "91" approx 87 MON

Running straight AV will probably give you diminished performance... and, IMO, you should run it as a mix in approximately the same proportions as you would for race gas.

For a detailed discussion of AV/PUMP/Race.. see this thread.

http://www.snowest.com/forum/showthread.php?t=220800









.

 

[BILTIT]

So basically 50av/50pump would be enough with 14.5 domes at 1850ft is what you are saying? Alittle more than what would be required if I used 110 race fuel mix.


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[philsummers21]

Have ran straight avgas for a couple years now. Prefer it over race fuel cause its way cheaper and easier to get.

 

[mountainhorse]

Phil...

Straight race in your Turbo??? (This is about an NA Sled)



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[AndrettiDog]

You run Av or race fuel to increase your octane level to avoid detonation. The stock Pro shouldn't have more than 91 octane at elevation (I'm at 9k+). I ran 88 non ethanol and that sled ran amazing. Additional octane is just a waste of money and the sled will not run as hot.

I would run 50% pump/Av fuel if I were you. Av fuel is cheaper and has lead for lubrication. If you get detonation, go up on the Av fuel.

 

[BILTIT]

I finally had a chance to read the link MH posted, fantastic! Thanks MH, that helps a lot.

I may just switch my pontiac 455 (11.8:1 comp) powered boat to AV gas vs the straight 110 I am using now.


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[Jay]

I've responded to several av gas threads over the years and I guess I'll throw my 2 cents in again. I have run av in every sled I have ever owned, from a stock 440 to full mod 650's, one '91rxl to mod 700/800's to W/C 1200 triples and soon in a ubr BB I'm working on. Every mixture from 100% to a couple of gallons in a tank. Av works great, is it as good as C112 or C114? no, but it's a very reasonable fuel for high compression engines to avoid detonation. I have never had ANY issues with using av, I've never had any issues with it being "dry", I've never seen it eat fuel lines or filters. I have come out of the cabin after the sled has been sitting, after riding all day in that real fine powder, the kind that gets into everything and freezes up throttles, carbs, etc. and my sled starts on 2 pulls and happily idles while everyone else is cursing and pulling a mile of rope out of their sled. I would run av in anything, anywhere, anytime, did I mention it works great? One thing I would say to Biltit is at your elevation with 13.5/1 compression I would run straight av and anything over that, like 14/1 or 14.5/1 I would step up to a 50/50 mix of C112 and good premium pump gas, at least that was the advice I was given by a very reputable engine builder. 14.5/1 at 1850' running 50/50 av and pump is not a good idea.

Edit: I never had any issues with plug fouling either, jet it right and your golden. Also as another guy pointed out av is kept very clean by the manufacturers/distributors. The local corner gas doesn't really worry about water or crap in their tanks but the FAA definitely gets unhappy when planes start falling out of the skies because of dirty fuel.

 

[BILTIT]

The 50/50 is just my guesstimate. I assumed since 25/75% of 110/91 is enough for the 13.6 head than a 50/50 of 110/91 would be enough for a 14.5. From what has been said av gas is close to the MON of 110 race.

I would start with 100% AV and reduce it until I saw DET or undesirable running characteristics and then add more back in.


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[w9]

Torco race fuel concentrate is a good option as well and is intended more for what your looking for than AV gas is.Mix the Torco with 91 and works out to 105 octane.