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PART 1: AV gas in a turbo 2 stroke

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mountainhorse

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JB, ask our buddy Allen how many sets of BPR9EiX's he went thru last season from lead fouling on 50/50 non-ethanol 91/110 Sunoco Std. mix @ 10lbs of boost in the BD PG D-8.

I guess some have a problem... some don't which is wierd to me.

100LL is rated 100/130 lean/rich still.

Good to hear about the cold start properties... I'm wondering what would have brought that about???
 
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adam5187

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Going back a few posts with the lubricity concerns of AV gas I am wondering if a few ounces of 2 cycle oil in with a tank would address this problem or not?
 
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cowboymann02

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So MH did we decide, if your going to run AVgas this year or are you going to stay with race fuel??? You said AV 100LL is about the same as VP mix at 103 octane by your figures correct. IF thats true i will probably run AV gas myself.
 

mountainhorse

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"110" race gas (105/6 MON) mixed 50/50 with 10% ethanol Pump-gas 91 (about 87 MON) ends up being around 97 MON (or slightly less)....

Whereas the straight 100LL will be around 104 MON.

I'm still looking for a more complete picture of the fuels capabilities and character in a 2 stroke large displacement twin.

IMO... The AV gas would be able to tollerate a couple more lbs boost than a 50/50 mix of pump/110 race gas. In fact... given the same boost level the 100LL might just have too HIGH a MON rating for optimum performance (see this post above CLICK HERE)

Can you "Over-Octane"an engine? If so, what happens?

Yes you can over octane an engine.

Generally you will get sluggish throttle response. Also you may get fouled plugs and deposits in the exhaust ports and headers.

When an engine is trying to burn a fuel that has too much octane, the burn rate is incorrect and all of the fuel won't be used up. This excess usually gets left as a deposit or gets pushed out the exhaust.

It is important to match your engine's needs with the correct fuel.
At lower boost levels...you would want to run a mix of 100LL (remember this is about 104 MON) and Pump Premium.

At 10 lbs of boost...Running straight race 110, I know that many people are realizing DECREASED performance compared to mix... That would be realized in top power as well as throttle "character"

In general, with 100LL having ONLY 2 MON points less octane than "110" race gas... the boost levels would only be slightly less for the AV gas... mixed or straight.



What are the experienced Polaris turbo users out there finding they are able to run for boost pressure on straight 110 RACE gas (no pump mix)???





...
 
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Super Dave3

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What are the experienced Polaris turbo users out there finding they are able to run for boost pressure on straight 110 RACE gas (no pump mix)???

12-16 lbs depending on elevation and how well your innercooler works.
 
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cowboymann02

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Outlaw what the hell do you know!!!!!!!!! you probalbly use marking paint to find you way out of the woods each year.... LMAO
Sorry couldn't pass up the cheap shot... what grade VP you running in your twister anyways for everyone to know? Straight Fuel, no mix correct?
 

mountainhorse

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OA.... How bout straight 110 race??...

Not looking for "maximum boost numbers possible with this engine on any fuel...just 110 as it is closest in MON to AV gas.

What are you running on max on 110 Race???
 
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Spaarky

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OMG.... thats not a max number. I have no problem running upwards of 20 for a long period of time.

Great, I run 114 instead of 110. Like I said IMO, that Garret turbo(guess I am assuming a bit what Dave runs) will give up on boost before the motor does. Do I have experience with 110... none, wouldnt touch it. We only run 114, for a long list of reasons. I was just comparing what Dave wanted to do, compared to what I have seen.

If you want to get technical about it, we need to know compression, squish, timing, before any true judgement can be made.

This is a great thread, but the fuel you are running doesnt mean dick, unless you are set up for it. Whether it is pump gas or straight race....

cowboymann02
Straight Fuel, no mix correct?

I garuntee you when you come to pick up your sled there will be straight 114 in it. Until you get comftorable with tuning, Rob will strongly suggest you run it.
 

mountainhorse

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OA.... Thanks for your input... always appreciated.

This is a great thread, but the fuel you are running doesnt mean dick, unless you are set up for it. Whether it is pump gas or straight race....

You are right on the money there.

The title of this thread is related to AV Gas though

110 (approx 106 MON) is approx the same MON # as AV Gas(104 MON)... of course, as I'm pointing out there are differences in the fuels.

I'm wondering, for those that run straight 110 Race with ZERO mix, (whatever brand) what boost levels are you running?
 
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mountainhorse

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From what I'm finding out from people that DO run the straight 110, with zero mix is that 11-13 lbs is where these machines want to run well.

Of course it also has to do with system design, state of tune, static compression, fuel mapping, charge temps etc... all of those will raise or lower the Octane dependency levels.

This is simply a 'rough idea' here that will, hopefully, shed some light on this topic outside of speculation and unsupported rumor.

Less than than that and they get Spongy on the throttle response as well as other "over octane" issues, more than that and deto problems start to pop up.

IMO, the reason to run AV gas would be, in large part, to avoid the ethanol in pump fuel and avoid the high cost and logistics of Race gas.

For those reasons, running it straight, Zero mix, seems to have advantages... BUT, and I know this cuts into the ego a bit, 11-12 lbs of boost will require a VERY skilled rider to pilot the sled in technical situations... Many riders just are not up to this level (yet) (me included)

IMO, Mixing AV gas with pump fuel will give you back some of the throttle character that we all like, but not get rid of the ethanol problems that are causing issues in our power sports equipment.

The weak link is Crappy 91 pump gas with ethanol and/or other poor performing oxygenates in it.

It would be nice if one of the race gas suppliers could provide a good quality, 91-94 octane (R+M/2 rating) that was designed for power-sports equipment, no-lead added, no oxygenates/ethanol AT a Reasonable price... VP and Sunoco both make this type of fuel but it actually costs significantly more than 110 Leaded Race fuel!!

There is no real easy answer here.
 
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cowboymann02

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Straight 114 it will be, did you get time to look at the sled build pics i have in the other member build forum. better put your shades on before you look at them. won't get lost in the snow thats for sure...............
 
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LT

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I just want say thanks to everyone who has put so much time and effort to shed light on this somewhat cloudy topic!

This is a great topic and ive learn a great deal about a topic that i had really no knowledge of at all.

Keep up the great work SW
 

guidoxpress

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would there be any difference in using AVGAS vs Race Fuel in a Big Bore vs a Turbo...

Carls recommends using 50/50 (91/110) for 5000ft-8000ft (ill have to dbl check the ranges) for their 975 big bores...

but i am about to use straight 100LL AVGAS after i get it tuned right...

but nothing on big bores here, just turbos...either way, IMO...avgas is the way to go
 

mountainhorse

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Guido... mix the AV 50/50 as well IMO.

The 100LL is 104 MON... 110 from VP and Sunoco is 107/106 MON respectively.

Hot topic these days, IMO... there will be some throttle response diff if you run too much octane in this setup.... I think that straight 100LL (104 MON) will be too much octane for optimal results... especially since you can find non ethanol pump for mixing in your area.

See the thread above.. some good info.
 

guidoxpress

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Guido... mix the AV 50/50 as well IMO.

The 100LL is 104 MON... 110 from VP and Sunoco is 107/106 MON respectively.

Hot topic these days, IMO... there will be some throttle response diff if you run too much octane in this setup.... I think that straight 100LL (104 MON) will be too much octane for optimal results... especially since you can find non ethanol pump for mixing in your area.

See the thread above.. some good info.

thats even better news then straight 100LL then...so 50% Avgas/50% 91 pump...good to know...

yeh sorry to hijack your thread guys, just not much help or talk about big bores and fuel setups....but when i turbo the other sled it will drink 100LL Avgas for sure...

this is the BEST AVGAS vs Race Fuel thread on here IMO...

MH you have gone above and beyond to get this detailed info, its great to you have around as always...
 
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