av gas vs 91 pump for 2013 stock pro

[Hillside]

I am looking at buying another pro, closeout and the dealer says they will include a full tank of av gas. But, will that high octane affect anything?

I love the idea of running one fuel for both sleds, my other is a turbo 2013 pro tuned for 100ll too.

But, i've never heard of a stock sled running this fuel. TIA

 

[ak]

Won't hurt anything. I would siphon it out and put in your turbo sled and save a few bucks.

 

[richracer1]

From what I've heard, AV & race gas are not very friendly to the OEM fuel filters. It destroys the filter media. Also, the way AV gas or race burns, it may cause a lean condition in an engine tuned for pump gasoline.

 

[mountainhorse]

I saw no degredation in with the AV gas... but in "HOT" (toluene rich) race blends... there were problems... some other SW members sent me their filters... cut open 2 filters that Had run AV for 1000 miles or so... no issues.... Low mileage stock filters on C12 were toast.

The AV Gas is good quality gas... but is WAAAAY over octane.... Premium 91 has a MON (motor octane number) of around 88.... 100LL has a MON of around 104.

It will run ok, but your throttle response will not be as crisp on the bottom end and sluggish in fast throttle transistions... from experience.




.

 

[Kcjepperson]

So is av gas better to run than race fuel? That what it's sounding like?

 

[philsummers21]

This makes no sense to include a full tank of Avgas on a new sled purchase. Av or race fuel will not create more hp in fact it makes less on a stock sled. There is no reason at all to run it.

Av vs racegas is no comparison. I believe avgas is better then MIXING 91 and race because you get a more conistent fuel. But straight avgas will not replace straight race 110 or higher. Most dont need to run straight race tho they blend.

 

[Kcjepperson]

I try and run a gallon of race fuel in every tank mainly because you never know what you get out of the pump. Would it be better mix in av gas. I live close to an airport as well as a place that sells all different octanes of fuel. I am running a gallon of 112 octane to every tank. Or about 10 percent depending how much fuel I need to fill up

 

[mountainhorse]

There are many different factors...

An engine is designed for a particular Octane and will run best with that octane.

There are different thermal properties to the different gasolines. Those properties affect how the engine runs, throttle response at diff rpm and different cooling aspects.

There is a very lengthy thread on the AV gas discussion in the turbo thread.

For all intents and purposes... stock sleds with stock timing curves and compression will not run as well on gas with too high of octane.




.

 

[winter brew]

FWIW, on the older Doo 800's that were designed to run on 87 octane, Doo's dyno testing showed a 4+ HP drop when running 91. I
I would have them skip the Avgas and ask for a gallon of oil instead.

 

[Hillside]

I don't think I'm going to buy the sled, its the end of the season and the last thing I need is another snowmobile. I mean shoot, I already have a 22k sled this year, maybe next year I will get a 163. The whole av gas thing is weird but I have heard it will run cleaner and in colorado it is so hard to find pump 91 without ethanol. You can turn off the timing key apparently so it does make a difference. I don't know but I carry a 55gal drum so running two sleds with av gas would be much easier then running one with 91 and the other av.

all very interesting

 

[Seeker]

Straight Av gas is all I run but I do mix a little bit of Polaris VES Gold in with it on every tank. My sled runs like a raped *** ape...No bogs, no crappy throttle response on bottom or top end, just very crisp all the time...The AV gas seems to stay fresh for a very long time as well. I stored it in my garage all summer long & it was like new 9 months later, unlike the skunky ethanol crap that goes south in a hurry.

Another huge benefit for me is that it does not give me headaches. I have spilled Av gas it on my hand a few times & you cannot even smell on your skin after it dries. If you spill the ethanol infused gas on your hand, it takes a month to get the stink off.

 

[POLZIN]

have them fill it wth AV when you summerize it. AV stores waaaay better than pump gas!

 

[AndrettiDog]

This makes no sense to include a full tank of Avgas on a new sled purchase. Av or race fuel will not create more hp in fact it makes less on a stock sled. There is no reason at all to run it.

Av vs racegas is no comparison. I believe avgas is better then MIXING 91 and race because you get a more conistent fuel. But straight avgas will not replace straight race 110 or higher. Most dont need to run straight race tho they blend.

It's amazing how many people don't get this. Race fuel or av gas doesn't make your sled run faster, technically it will run cooler and produce less HP. You run race or av fuel because your motor requires it (with high comp heads or turbo setups). Whoever is adding race fuel to ethanol fuel or lower octane fuel is getting an overall less ethanol diluted fuel and/or a higher octane mixture. This can be good depending on what you need, but doesn't produce more power. Just keeps the motor from detonation.

Av fuel often has lead in it. Make sure you don't use it in your car as it will tear apart your cat converter. I've been told that the lead fuel is good for lubrication.

 

[jims68]

AV gas

Your 0'2 sensors can act up too. Took some out of a race sled and dumped it into my Hyundi and threw a 02 code that next day. Filled car up with 89 and cleaned 02 sensor. Was lucky that time and later told same on cats will plug up because of the lead. I use it as a stabilant yet. One gallon to every five max in my generators and lawn mowers and such. My Lincoln welder\generator is at least 5 years old and still smells sweat and gas looks good yet. Wouldn't reccomend that but is used more as a standby then a welder. People come looking for the race gas smell when you are out camping too! We use to race extensivly with av gas before DI ignition but you need to be on top of your timing and jetting or they fall flat on there faces like 10 lengths in the 660 bad! Realy messed with tech in the day too! Cheaper then VP or other race furmulated gas too if you can buy it at an airport.

 

[cateye5312]

There are many different factors...

An engine is designed for a particular Octane and will run best with that octane.

There are different thermal properties to the different gasolines. Those properties affect how the engine runs, throttle response at diff rpm and different cooling aspects.

There is a very lengthy thread on the AV gas discussion in the turbo thread.

For all intents and purposes... stock sleds with stock timing curves and compression will not run as well on gas with too high of octane.


.

My old physics teacher always said to run the lowest possible octane that didn't cause knocking as that would perform the best in that particular engine. Don't know if I would go that radical on a sled but his comment leads me to believe there is something to Mountainhorse's points.

 

[Scott]

My old physics teacher always said to run the lowest possible octane that didn't cause knocking as that would perform the best in that particular engine. Don't know if I would go that radical on a sled but his comment leads me to believe there is something to Mountainhorse's points.

I've always heard it that way too. Run as low as possible.

 

[RMK935VA]

Just like MH and others said, running higher octane than recommended will likely cause the sled to run worse not better. The oil companies would love for everyone to put in higher octane fuel because they make more money on it. Do what the manufacturer recommends period. Otherwise, you are spending more money and making less power. That is silly. However, the comment that Av Gas will last longer is correct. It is manufactured to not lose octane or attract moisture over long periods of inactivity. That makes great sense for an airplane. I think that using Stabil is a cheaper option for long periods of inactivity (storage, summer, etc.).

 

[jims68]

av gas

You guys are on the right track! Remember the old leaded regular gas? If I remember right it was 82 or 83 Octance MON and the mottocross guys used this fuel alot. Test showed it burned the hottest which converts to more thermal energy. I could get away with 50\50 mix with premium or VP red any stronger and I would loose the exhaust side of the pistons at about 550 feet of course in the lead! Problem was I was running cast pistons per improved rules and forged would of worked. If it was really cold I mean 20 below cold I could do the 660 but only a few times then loose the top ring. Oxy-Propelene was the ticket but VERY illegal and highly toxic plus only lasted a few hours after mixing. Ahh the good old days and I'm only 44!!!

 

[Kcjepperson]

I don't know anyone that wants to run race gas/av because its cool, I run a gallon just to offset the who knows what you'll get out of the hose dilemma. I am starting to decrease the amount I use slowly to see if I do hit det with the 910. I haven't had one det so far and I have been riding twice a week for the last two months.

How would changing timing affect running race/av gas?

 

[mountainhorse]

Octane is not the only characteristic that affect the "fitness for use"... Different gasolines have different thermal properties in the blends that affect things like throttle character, amount of heat produced, vapor lock, combustion heat etc.

You can have two different fuels with the same Octane (weather you are measuring RON, MON or R+M/2)... but work very differently in the engine.

Some things to "Chew on"

What does octane really measure and how important is it?

One of the most frequently asked technical questions we get at VP involves the difference between Motor, Research and R+M/2 Octane Numbers. The next most frequently asked question is why some fuel companies represent their fuels with Motor Octane Numbers, while other companies use Research or R+M/2 Octane Numbers.



Realize first that octane is a measurement of a fuel’s ability to resist detonation—nothing more. The two types of machines used for testing octane—a Motor Octane machine and a Research Octane machine—were designed in the 1930s. They were designed to test for octane numbers from the 0-100 range, therefore, any number above 100 is an extrapolation.

Both of these machines are dinosaurs and are not adequate for today's high tech fuels or engines, but they’re the only means available for testing fuels. These machines are one-cylinder engines with an adjustable head that can move up or down to increase or lower the compression ratio while the engine is running. The Motor and Research machines are the same in this respect, but they differ in several other characteristics. 



The following is a comparison of the two machines used for testing octane numbers:
---------------------- Motor Octane Machine --------- Research Octane Machine
RPM --------------------------900------------------------------ 600
INTAKE TEMP.---------------300 DEGREES F -----------------120 DEGREES F
TIMING --------------------VARIABLE BASIC------------------FIXED AT 13 DEGREES
(DOES NOT CHANGE)
----------------------------SETTING 26 DEGREES

As you can see, the Motor Octane machine runs at a higher RPM, higher temperature and more timing. This machine puts more stress on the fuel than a Research machine and more accurately simulates a racing engine. VP Racing Fuels always includes Motor Octane Numbers when promoting its fuels because our fuels are used exclusively for racing applications.

The Research Octane machine will always produce a higher number for the obvious reason that it does not put the same amount of stress on the fuel. This number is used by some fuel companies to trick the racer into thinking the fuel is rated higher, i.e., higher quality, than it really is. The “R+M/2” Octane Number is the average of the Research and Motor Octane numbers for a fuel and is the number displayed with yellow labels on retail level gas pumps.

When comparing fuels for racing purposes make sure to compare Motor Octane Numbers because these are the ones that count in your racing application. Focusing on the MON of each fuel will help ensure you’re comparing apples to apples with regard to octane.

But bear in mind, a fuel’s ability to prevent detonation is a function of more than just octane. For example, VP’s fuels—oxygenated or nonoxygenated—vaporize much better than competitive fuels with comparable octane ratings. This means VP fuels cool the intake charge, burn faster and yield more efficient combustion. As a result, the “effective” octane rating of VP’s fuels is even higher than the rating generated by the octane test. As a result, VP fuels will prevent detonation more effectively than competitive fuels with comparable MONs.

Besides octane, what else do I need to consider when selecting a fuel ?

Too often, racers focus only on octane when evaluating the quality of a fuel. Octane is certainly important, but it’s just one of several key fuel properties that should be considered when evaluating and selecting a fuel. It’s entirely possible to generate more horsepower with a lower octane fuel if it’s designed properly with respect to its other key properties. It’s also possible for two fuels to have the same octane rating, but perform very differently due to their other key properties.

1. OCTANE: Octane is simply a rating of a fuel’s ability to resist detonation and/or preignition. It is not so much an indication of a fuel’s ability to make power, but rather a fuel’s ability to make power safely, i.e., without blowing your engine. Octane is rated in Research Octane Numbers (RON), Motor Octane Numbers (MON) and Pump Octane Numbers (R+M/2). A Pump Octane Number is the number you see on the yellow decal at gas stations, representing the average of the fuel’s RON and MON. (See below for a more detailed explanation of how octane numbers are derived and what they represent.)

VP relies on MON numbers because the MON test more accurately simulates racing conditions. Don't be fooled by high RON or R+M/2 numbers. Many companies use these simply because they look higher and are easier to come by because of the test methods. Also bear in mind that the ability of fuel to resist detonation is more than just a function of octane.

2. BURNING SPEED: This is the speed at which fuel releases its energy and is partially a function of a fuel’s vaporization qualities. At high RPMs, there is very little time (real time - not crank rotation) for the fuel to release its energy. Peak cylinder pressure should occur around 20˚ ATDC. If the fuel is still burning after this, it’s not contributing to peak cylinder pressure, which is what the rear wheels see. Because VP’s fuels are designed with a particular focus on vaporization characteristics, most of VP’s fuels—oxygenated or nonoxygenated—vaporize much better than comparable competitive fuels. This means it cools the intake charge, burns faster and yields more efficient combustion. As a result, the “effective” octane rating of VP’s fuels is even higher than the octane test indicates, and they will prevent detonation better than competitive fuels with similar MONs.

3. ENERGY VALUE: Energy value is an expression of the potential energy in fuel. The energy value is measured in BTUs per pound, not per gallon. The difference is important as the air/fuel ratio is in weight, not volume. Generally speaking, VP’s fuels measure high in BTUs per pound and thus, have a higher energy value. This higher energy value will have a positive impact on horsepower at any compression ratio or engine speed.

4. COOLING EFFECT: The cooling effect of fuel is related to the heat of vaporization. The higher a fuel’s heat of vaporization, the better its ability to cool the intake mixture. The superior vaporization characteristics of VP’s fuels make cooling effect one of their key advantages. A better cooling effect can generate some horsepower gains in 4-stroke engines and even bigger gains in 2-stroke engines. VP’s superior cooling effect can also ensure circle track racers maintain power in the longest races and harshest conditions. In virtually any application, the cooling effect of VP’s fuels will help extend engine life.

Understanding these key properties of fuel will better equip you to evaluate fuels for your application. By clicking on your application to the right,
you’ll find a list of VP fuels designed with you in mind, along with the fuels’ relevant characteristics.
....

More (Octane) ISN'T always better!!

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.

I've been diving into the whole Aviation gas thing... trying to learn as much as I can... It takes a bit of digging to find relevant information.

Since I'm a newby to the fuel thing and didn't spend much time on this in my engineering coursework ...I'm definitely open to critique from those in the know.

I was able to find out that the "100" in the 100LL name is actually NOT a standard MON or RON octane number...It is a "Lean Octane Number" (LON) and NOT actually MON (Motor Octane Number)

Conoco-Phillips rates their 100LL fuel at 99.5 "LON".
See this Document for information from Conoco ...CLICK HERE

I did however find another document by Conoco Phillips that actually ran a formal Motor Octane (MON) test on thier same 100LL "AV Gas" when they were working on testing the viability of Aviation Grade Ethanol (AGE). CLICK HERE FOR THIS DOCUMENT... It will open up in a word document.

It shows the results of their MON testing on their 100LL Aviation Fuel.

The Difference in this test is that that they varied the intake temp but found the 100LL to be very stable over a temp gradient... The MON of 100LL in the testing by Conoco-Philips was 104 at the standard 300 degree intake temp used on all other MON testing...

My biggest concern with this fuel is throttle response from the higher evap temps.

As a direct replacement for pump 91... I'm still not sure... for a mod motor with Higher compression or turbo applications... it is growing on me.

I'm starting to wonder if there is any kind of additive that will reduce the Evap temps and improve the throttle response of AV gas.

With the increasingly poor quality of pump gas, the ethanol in today's pump gas that seems to be raising havoc and the relatively cheap price of AV Gas at around $4.60/US Gallon compared to race fuels... The AV Gas is peaking a lot of peoples interest. ...prices from 100LL.com

Here is a good post from Sherrif on the forums here.

Fuel Terminology (maybe some clarification for you guys)

Fuel Terminology & Definitions:


OCTANE
Below is a more detailed explanation of the types of octane. Generally, Octane is rated in Research Octane Numbers, (RON), Motor Octane Numbers, (MON) and Pump Octane Numbers (R+M÷2). Pump Octane numbers are what you see on the yellow decal on your local gasoline pump and represents the average of the (RON) and (MON). (RON) is generally the higher number and is the number many companies choose to use advertising their products, however (MON) is the octane number more relevant to racing as it is one of the factors that represents the fuel's ability to resist preignition. Other important factors related to a fuel's ability to make power and resist preignition are listed below including BURNING SPEED, ENERGY VALUE and COOLING EFFECT. SEE OCTANE REQUIREMENTS BELOW.

Motor Octane (MON):
(a) CFR Tested @ 900 rpms, timing is varied with compression ratio, fuel is preheated to 300 degrees Fahrenheit, intake air is preheated to 100 degrees Fahrenheit.
(b) Motor Octane, measured under varying load is definitely the most representative octane measurement for actual engine octane requirements.
(c) The closer the Motor Octane number to the Research Octane number the more stable the fuel is throughout the RPM range . This is very critical when running higher that 7500+ RPM's engine speed. (See the Octane Differential in the chart above)
R+M÷2 Octane (R+M/2):

RESEARCH Octane numbers
(a) This method of measurement consists of adding together both the MOTOR and and then dividing by two.
(b) This is the number in that yellow box that you see on the gas pumps.
(c) This number should only be used when determining which fuel to use in your street car or tow vehicle. This method is NOT intended for correct use in your racing engine.

Research Octane (RON):
(a) CFR tested @ 600 RPM's, fixed timing at 13 degrees BTDC, fuel temp is not controlled and intake air is varied with the barometric pressure.
(b) This is basically a No-Load test and this number should NEVER be used to determine which fuel to use in your race engine.

Specific Gravity (SG):
Density of the fuel.
(a) This is the weight of fuel compared to water, water being at 1.00. If race fuel is .750 (specific gravity) it would weigh ¾ the weight of water. If water at 60 degrees Fahrenheit weighs 8.125 pounds per gallon (ppg), then race fuel at .750 will weigh 6.09 (ppg).
(b) The less dense the fuel (lower specific gravity) the higher the BTU content and the better the stability of the fuel at higher RPM's.
(c) The lower the specific gravity of the fuel, the more crucial the jetting becomes, and the easier it is to run the engine lean, possible causing internal damage.
(d) The combustion speed is determined primarily by the pressure (density) of the fuel mixture. A lower (SG) or viscosity fuel will flow more through an orifice (jet) and a higher (SG) or viscosity will flow less.
Lead Content (LC):

Amount of Tetraethyl Lead in grams per gallon.
(a) When lead is added to fuel, the knock resistance (anti-knock value) is increased. Lead is also used to increase the octane to a higher number.

Reid Vapor Pressure RVP:
The pressure of the fuel. The tendency of the gasoline to evaporate. Too high of a RVP may cause the fuel to boil or evaporate in the pump, lines or carburetor at a given temperature which can lead to "vapor lock". Too low of a RVP and the fuel will not vaporize and could cause difficulty starting the engine when cold. Most Racing Fuels have an RVP in the range of 5 to 7.

Color
Simply the physical appearance color of the fuel.

Dielectric
The electrical charge of the molecules within the fuel. These are approximated numbers of the fuel dielectric value when using a HDE G-01 Fuel Analyzer. The accuracy of fuel checked should be within +/- 0.4 points. When two stroke oil is added to the fuel the meter reading will be INCREASED by 0.1 to 0.2 points depending on the type and ratio of the two stroke oil. The 2 stroke oil may also significantly change the color. Fuel additives will also change meter reading from that of untreated fuel.

Consistency:
It is very important that the fuel you use maintain the purity and consistency regardless of which brand fuel you use. Try to purchase fuel that has been stored in sealed containers and a high volume dealer. Open or bulk fuel storage tanks may have a tendency to sweat and produce moisture, therefore changing the consistency or purity of the fuel. If at all possible buy your fuel in a factory sealed drum although the cost is generally higher but the quality may well be worth it in the long run.

Burning Speed:
Burning Speed is the speed at which fuel releases its energy. In a high speed internal combustion engine there is very little time (real time - not crank rotation timing) for the fuel to release its energy. Peak cylinder pressure should occur around 20 degrees ATDC. If the fuel is still burning past this point, it will not contribute to the peak cylinder pressure thus it is not contributing to the power output of the engine. Too fast of a burn or too slow of a burn of the fuel will result in less than optimum power.

Energy Value:
Energy value is an expression of the potential energy in the fuel. This energy is measured in BTU's (British Thermal Units) per POUND, not per gallon. This data is important as Air Fuel (AF) ratio is measured in weight and not volume. This value may vary with compression ratio and engine speed.

Cooling Effect:
Cooling effect of the fuel is related to the heat of vaporization. The higher the heat of vaporization, the better its effect on cooling the intake mixture for a denser charge. This is of some benefit in 4-stroke engines, but can be a large source of gain in 2-stroke engines.

Knock - Detonation - Ping
Intense pressure within the cylinder due to inability of fuel to have a controlled burn This could be caused by to low of an octane fuel for the application or incorrect tuning procedures. The sound you hear is from the actual vibration of the cylinder walls or the fuel exploding micro seconds prior to timed ignition firing which may cause two intense high pressure waves to collide or clap together and the colliding energy wave produces the sound you hear. This is hard on an engine. It is just like taking a ball peen hammer to the pistons. Use of proper fuel and tuning techniques will control this situation. Excess oil in the cylinder due to poor ring seal can cause detonation.

Pre - Ignition
Pre-ignition is the premature ignition or lighting of the mixture in the cylinder. This condition takes place prior to the spark plug firing. It is usually caused by a deposit or object glowing in the combustion chamber. A overheated spark plug or incorrect tuning parameters can cause preignition. This condition usually occurs while the piston is traveling up during the compression cycle. Pre-ignition may cause the piston to attempt to change directions which can cause major mechanical damage within the engine. Pre-ignition is much different that detonation although they both can reak havock on your engine.

Octane Requirements -
Fuel Needs
The required octane is one that provides a controlled burn throughout the power cycle of the engine. As noted above octane, is not the only factor within the fuel that controls the burn and there are many factors within the engine that affect the burn rate which then affect the amount of octane or burn control required. These factors include, but may not be limited to, engine compression, camshaft timing, ignition timing, combustion chamber design, spark plug location, valve adjustment, engine operating temperature, fuel mixture, and weather. Extremely high octane is not best for performance.

A higher octane slows the burn rate and conversely a lower octane quickens the burn rate. You desire a burn rate that will match the needs and characteristics of your engine so that you may produce the maximum amount of power, but at the same time retain reliability. It is better to error to the higher side of the octane instead of the lower.

Normally a margin of safety is desired just in case the air gets really dense or the engine temperature climbs a little high to prevent detonation in these instances

I am just wondering if running pure av gas in a 2 stroke turbo is a cheaper alternative to a 50/50 race fuel/premium mix. I can get it here in Alberta for 1.46 per litre, so any info or problems would be appreciated, thanks. I will be running 12lbs of on d7 with a silber kit.

Thanks man...

Just trying to find out for myself too.

To answer the original question...100LL straight will have Higher MON than a 50/50 mix of 91-pump / 110 VP/Sunoco (both around 106-107 MON)

Straight AV-Gas 100LL has an MON of approx 104 when measured using the same standards as other motor gasoline... not the Aviation lean/rich numbers that 100LL is usually rated with.

As a side note...
VP 110 is 110 R+M/2 octane... 107 MON, 113 RON

Sunoco Standard 110 is 110 R+M/2 octane... 106 MON, 114 RON

Both fuels will have different running character... they both (VP/Sunoco) have significantly different Reid Vapor pressures, 90% evap #'s and some other properties that can affect performance... which one is better for MY kind of riding.... I don't know (yet)

I would expect these two different brands of 110 to run differently in the same sled.

SNOW JW :As far as dry, throttle response ect. maybe siting on a dyno with a magnifying glass you may get a wee bit more throttle response if any but for the average sled it's a great turbo fuel and as long as you have some cold charge temps it's very surprising how far you can push the fuel before you get into some DET.

Also with some searching on SW you will find there are many guys that run Av gas with allot of years and miles on there sled and never had a fuel related issue.

Barnes... I'm looking for good reasons to use the AV-fuel too.

I've heard the "dyno/magnifying" argument ... but no side by side testing on the mountain on the same sleds or in the same sled, same day.

Also... 100LL should not give you fuel related issues... it is generally very high Quality fuel, stable, and higher octane...

It does have lead, as mentioned above, some plug fouling will happen.

average sled it's a great turbo fuel and as long as you have some cold charge temps it's very surprising how far you can push the fuel before you get into some DET.

The AV gas with it's higher boiling point will actually resist deto more than straight Race 110... due to the higher distil temps (evap temps)... From what I'm finding out (slowly) is that with 100LL you can actually have liquid fuel hitting the dome and cooling the comb chamber.

My concern with the 100LL is Not the WOT running or det protection... it is the radical throttle swings in high-load boondocking... ie, throttle response. Although it may run "well" how is it compared to race gas straight or in 50/50 blend in large throttle position swings.

100LL is only 2 MON octane points lower than Sunoco Standard with different properties.

Here is a great post that spurred me on to look into this more... this guy really knows his stuff and backs it up with solid information.

CLICK HERE...Great, easy reading.

This was written before ALL pump fuel had ethanol in it... If someone has a local pump that THIS SEASON has non ethanol... let me know what location and station you can get it from... Help some fellow sledders out!

"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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