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Old 01-11-2013, 08:59 AM   #1 (permalink)
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High octane gas

Some people say it's good to run a higher octane gas in snowmobiles and others say never to do it. I know that my grandfather runs airplane fuel in his snowmobile. Is that safe? He tells me I should use it in mine, but I don't know if it is safe or not. Also, what is a good ethanol treatment to use when I do get regular pump gas?
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Old 01-11-2013, 09:14 AM   #2 (permalink)
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I wouldn't run anything over 93 oct. Aviation fuel is going to give u preignition. And u will melt down the motor, almost literally. When using pump gas I always throw in a bit of sea foam and stabil.


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Old 01-11-2013, 11:21 AM   #3 (permalink)
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I wouldn't run anything over 93 oct. Aviation fuel is going to give u preignition. And u will melt down the motor, almost literally. When using pump gas I always throw in a bit of sea foam and stabil.


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Thats what I thought. Thanks

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Old 01-11-2013, 11:22 AM   #4 (permalink)
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I think it would be safe to say never run straight av gas unless your sled is high performance and built specially to run the stuff. What is it, like somewhere around 114 octane? I've heard of guys mixing 50/50 regular and av gas in their muscle cars with stock motors that are around 10:1 compression and a little higher... Haven't heard of anyone doing it in their sleds. Not saying it isn't being done.

Is that a 998cc 4 stroke? If so, you're about 12:1 compression like mine. Not sure what the compression ratio is in 2 strokers.
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Old 01-11-2013, 11:26 AM   #5 (permalink)
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I think it would be safe to say never run straight av gas unless your sled is high performance and built specially to run the stuff. What is it, like somewhere around 114 octane? I've heard of guys mixing 50/50 regular and av gas in their muscle cars with stock motors that are around 10:1 compression and a little higher... Haven't heard of anyone doing it in their sleds. Not saying it isn't being done.

Is that a 998cc 4 stroke? If so, you're about 12:1 compression like mine. Not sure what the compression ratio is in 2 strokers.
Yeah its 114 I think. I thought that was pretty high. My grandfather runs straight av in all his street rods and in his boats as well, he swears by the stuff. And yeah his sled is an '03 Rx-1

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Old 01-11-2013, 11:36 AM   #6 (permalink)
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His RX1 is stock? I wonder if he had to re jet it. I know I couldn't get myself to do it. Besides, gas is spendy enough w/o paying bigger bucks for av gas..... After further research, it looks like you have a 2 stroke.... I wasn't sure.....
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Old 01-11-2013, 11:41 AM   #7 (permalink)
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His RX1 is stock? I wonder if he had to re jet it. I know I couldn't get myself to do it. Besides, gas is spendy enough w/o paying bigger bucks for av gas..... After further research, it looks like you have a 2 stroke.... I wasn't sure.....
Yeah his Rx1 is stock and no he didn't re jet. And yeah sorry I have a 2 stroke.

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Old 01-11-2013, 11:58 AM   #8 (permalink)
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So here is the very short answer to high octane fuels. Unless your engine is designed for it and requires it, you are LOSING power by running it. Octane is basically the fuel's resistance to burn. You need higher octane when you run more pressure, because of either a high compression ratio, or a turbo charger. If the engine is designed to run fine on 87 octane, 91 octane will give you less power, and even less on av gas.


(disclaimer, some engines can advance the timing to take advantage of it, but as far as I know, there are zero snowmobile engines that have knock sensors and are capable of advancing/retarding timing automatically based on sensor input) Even on the engines that do this, they won't go much past what 91 octane gives you, av gas won't make a difference.
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Old 01-11-2013, 12:03 PM   #9 (permalink)
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So here is the very short answer to high octane fuels. Unless your engine is designed for it and requires it, you are LOSING power by running it. Octane is basically the fuel's resistance to burn. You need higher octane when you run more pressure, because of either a high compression ratio, or a turbo charger. If the engine is designed to run fine on 87 octane, 91 octane will give you less power, and even less on av gas.


(disclaimer, some engines can advance the timing to take advantage of it, but as far as I know, there are zero snowmobile engines that have knock sensors and are capable of advancing/retarding timing automatically based on sensor input) Even on the engines that do this, they won't go much past what 91 octane gives you, av gas won't make a difference.
Thanks for the info. I'll just run 87 in it then and not waste my money on higher octane.

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Old 01-11-2013, 12:54 PM   #10 (permalink)
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Yeah his Rx1 is stock and no he didn't re jet. And yeah sorry I have a 2 stroke.

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I wonder if your dad gets away with it because he runs a 4 stroke? I'm guessing the compression ratio is higher on a 4 stroke than a 2? The only reason I say that is, my 4 stroke's compression is over 200psi per cylinder.

I'm still curious to know what the CR is on "stock" 2 strokes. I'm sure it varies, but what are some numbers? Anyone?

I've always heard too the more octane you use the cooler the engine runs. I think there are more ramifications than just not utlilizing all the octane in straight av gas if you run it in a sled. I'm with weasel, I bet you'd burn 'er down....

Hope I'm not hijacking your thread Vipersx..........
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Old 01-11-2013, 01:00 PM   #11 (permalink)
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I wonder if your dad gets away with it because he runs a 4 stroke? I'm guessing the compression ratio is higher on a 4 stroke than a 2? The only reason I say that is, my 4 stroke's compression is over 200psi per cylinder.

I'm still curious to know what the CR is on "stock" 2 strokes. I'm sure it varies, but what are some numbers? Anyone?

I've always heard too the more octane you use the cooler the engine runs. I think there are more ramifications than just not utlilizing all the octane in straight av gas if you run it in a sled. I'm with weasel, I bet you'd burn 'er down....

Hope I'm not hijacking your thread Vipersx..........
No your not, I like all the info. Im not sure about the cr on a 2 stroke. Im going ti look it up and see what I find.

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Old 01-11-2013, 01:07 PM   #12 (permalink)
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According to the owners manual #1 cylinder is 5.8:1 and #2 and 3 are 6.6:1

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Old 01-11-2013, 01:54 PM   #13 (permalink)
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Wow, that's a lot less than the RX1s and I assume 4 strokes in general. Since high compression likes high octane may explain why the stock 2 strokes would grenade and your dads doesn't... Still not going to try av gas...... Thanks for the info....
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Old 01-11-2013, 02:15 PM   #14 (permalink)
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Just one more thing. I know he talked my cousin into using av fuel in his sled which is a '95 zr 700 and he has had no problems so far, but has only been out once this year so far. I'll warn him about it and see what happens. Thanks for all the replies.

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Old 01-11-2013, 04:21 PM   #15 (permalink)
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for summer storage only , i put 5 gal. of av gas in sleds , it has no ethanol so i do not worry about phaze separation. i start them once a month for a few min. and yes it has a advance key. i add pump gas for running in winter .
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Old 01-11-2013, 04:30 PM   #16 (permalink)
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for summer storage only , i put 5 gal. of av gas in sleds , it has no ethanol so i do not worry about phaze separation. i start them once a month for a few min. and yes it has a advance key. i add pump gas for running in winter .
Yeah thats a good idea.

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Old 01-11-2013, 06:03 PM   #17 (permalink)
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I've always heard too the more octane you use the cooler the engine runs. I think there are more ramifications than just not utlilizing all the octane in straight av gas if you run it in a sled.

If you are talking just gasoline, and making zero engine changes, higher octane will slightly reduce your cylinder temperatures, and slightly increase your EGT's. Higher octane gas will ignite later and burn slightly slower, so there is more energy going out the exhaust pipe. The lower temps are just because you are changing where the gas is being fully used up.

Now if you are talking about running e85 (rocket fuel in the turbocharged car world!), that will result in substantially lower head and EGT's. At least in my car, I'm around 1650 EGT on pump gas, and 1450-1500 on e85.
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Old 01-11-2013, 07:08 PM   #18 (permalink)
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Anything over 10:1 compression will require higher octane fuel. Av gas is not necessarily higher octane.

Avgas is gasoline fuel for reciprocating piston engine aircraft and is not to be confused with jet fuel. As with all gasolines, avgas is very volatile and is extremely flammable at normal operating temperatures. Procedures and equipment for safe handling of this product must therefore be of the highest order.

Avgas grades are defined primarily by their octane rating. Two ratings are applied to aviation gasolines (the lean mixture rating and the rich mixture rating) which results in a multiple numbering system e.g. Avgas 100/130 (in this case the lean mixture performance rating is 100 and the rich mixture rating is 130).

In the past, there were many different grades of aviation gasoline in general use e.g. 80/87, 91/96, 100/130,108/135 and 115/145. However, with decreasing demand these have been rationalised down to one principle grade, Avgas 100/130. (To avoid confusion and to attempt to eliminate errors in handling aviation gasoline, it is common practice to designate the grade by just the lean mixture performance, i.e. Avgas 100/130 becomes Avgas 100). More recently, an additional grade was introduced to allow one fuel to be used in engines originally designed for grades with lower lead contents: this grade is called Avgas 100LL, the LL standing for 'low lead'.

All equipment and facilities handling avgas are color coded and display prominently the API markings denoting the actual grade carried. Currently the two major grades in use internationally are Avgas 100LL and Avgas 100. To ease identification the fuels are dyed; for example Avgas 100LL is colored blue, while Avgas 100 is colored green.
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Old 01-11-2013, 07:39 PM   #19 (permalink)
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Anything over 10:1 compression will require higher octane fuel. Av gas is not necessarily higher octane.

Avgas is gasoline fuel for reciprocating piston engine aircraft and is not to be confused with jet fuel. As with all gasolines, avgas is very volatile and is extremely flammable at normal operating temperatures. Procedures and equipment for safe handling of this product must therefore be of the highest order.

Avgas grades are defined primarily by their octane rating. Two ratings are applied to aviation gasolines (the lean mixture rating and the rich mixture rating) which results in a multiple numbering system e.g. Avgas 100/130 (in this case the lean mixture performance rating is 100 and the rich mixture rating is 130).

In the past, there were many different grades of aviation gasoline in general use e.g. 80/87, 91/96, 100/130,108/135 and 115/145. However, with decreasing demand these have been rationalised down to one principle grade, Avgas 100/130. (To avoid confusion and to attempt to eliminate errors in handling aviation gasoline, it is common practice to designate the grade by just the lean mixture performance, i.e. Avgas 100/130 becomes Avgas 100). More recently, an additional grade was introduced to allow one fuel to be used in engines originally designed for grades with lower lead contents: this grade is called Avgas 100LL, the LL standing for 'low lead'.

All equipment and facilities handling avgas are color coded and display prominently the API markings denoting the actual grade carried. Currently the two major grades in use internationally are Avgas 100LL and Avgas 100. To ease identification the fuels are dyed; for example Avgas 100LL is colored blue, while Avgas 100 is colored green.
I know the stuff my grandfather uses is clear. Any idea what octane that might be?

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