850 octane recommendations

snobyrd · Dec 14, 2018

The manuel says 87 or 91 can be used , but 91 is Recommended in the engine specifications,But in another part of the owners manual it says to use 91 octane to prevent poor engine performance and bad fuel economy. The manual is conficting itself. Does anybody know the compression ratio of this engine? In my opinion, 87 should offer better performance at Altitude than 91, the engine should be equipped with a det sensor , as we know more or octane does not equal more power, only a more stable combustion chamber, What is everyone’s opinion on this.

ripnit · Dec 14, 2018

Can run 87 if have to(I my self would run it in eth mode whether it's ethanol gas or not).....best to be safe and run 91 if available. My .02

NoNonsense · Dec 14, 2018

snobyrd said:
In my opinion, 87 should offer better performance at Altitude than 91, the Sanjan should be equipped with a det sensor , as we know more or octane does not equal more power, only a more stable combustion chamber, What is everyone’s opinion on this.

That's not at all true.. octane is resistance to knock.. more knock resistance means optimized ignition for greater indicated power, lower indicated specific fuel consumption, etc. Most OE powersports applications will design a combustion chamber and develop a calibration optimized for 91 oct pump gas. In this instance, you aren't gaining anything running race gas, but you will lose performance and increase likelihood of knock if you run 87 oct. Yes, the knock sensor should catch it, but it's after the knock event happened and it will pull timing and ultimately lose some performance.

It is true that you're less likely to have knock with lower atmospheric pressure, but you're definitely not going to have a performance gain with lower octane pump gas.

Devilmanak · Dec 14, 2018

NoNonsense said:
That's not at all true.. octane is resistance to knock.. more knock resistance means optimized ignition for greater indicated power, lower indicated specific fuel consumption, etc. Most OE powersports applications will design a combustion chamber and develop a calibration optimized for 91 oct pump gas. In this instance, you aren't gaining anything running race gas, but you will lose performance and increase likelihood of knock if you run 87 oct. Yes, the knock sensor should catch it, but it's after the knock event happened and it will pull timing and ultimately lose some performance.

It is true that you're less likely to have knock with lower atmospheric pressure, but you're definitely not going to have a performance gain with lower octane pump gas.

You didn't read his post. ALTITUDE. I have two supercharged F150 trucks, I tune them with gas, depending on current setup and ECU tune. A lot of the time at 5000 feet elevation, they run better on 87 or 89 octane than the "required" 91.

NoNonsense · Dec 17, 2018

Devilmanak said:
You didn't read his post. ALTITUDE. I have two supercharged F150 trucks, I tune them with gas, depending on current setup and ECU tune. A lot of the time at 5000 feet elevation, they run better on 87 or 89 octane than the "required" 91.

There is chemically no advantage to running lower octane fuel, including elevation and especially when boosted. You're either calibrating poorly or the lower octane fuel has ethanol content. There is literally zero evidence that can dispute this aside from people on the internet that don't understand fuel properties or thermodynamics giving their opinion.

AndrettiDog · Dec 17, 2018

In my past Polaris 800's, I could run 87 non ethanol fuel with no head on the non ethanol setting above 10k. Ran like a raped ape! I'm not a thermodynamic whatever, but to me you want to run hot without any detonation or risking the motor. I put 2800 miles on a Pro this way.

revrider07 · Dec 17, 2018

Fuel to air ratio low octane burns cleaner with correct ratio for compression.

NoNonsense · Dec 18, 2018

revrider07 said:
Fuel to air ratio low octane burns cleaner with correct ratio for compression.

I'm beating a dead horse here, but octane has nothing to do with burning cleaner or changing A/F ratio. Octane is an additive difference. There is no significant change in HC content.

87e10 will burn "cleaner" (leaner) than 91e0 because it is oxygenated, but no different than 91e10 aside from the fact that the 87oct is more prone to knock/pre-ignition.

knikflyer · Dec 22, 2018

In Alaska we can only get max 90 octane pump gas (no ethanol). Since i buy 100 LL Avgas in bulk for my other hobby i usually throw 1 to 1.5 gallons of it in each tank fill to give me a little more octane margin. I have had no issues doing this.

Jaynelson · Dec 22, 2018

Call me crazy, but I puts the 91 in it and runs it on the 91 setting. We ride at 5-7,000' ....but often have to start out at 2-3k'

Snowbird11 · Dec 23, 2018

i'm not well versed on the subject but my 2017 800 would pull 50-100 more revs on 91 ethanol vs 88 non-eth (8k-11k elev). i run non-eth in all my small engines and anything that may have fuel sitting in it for more than 6 weeks. that has eliminated many carb rebuilds and the constant need for injector cleaner in my engines. if i do have ethanol sitting in my tanks i try to have them completely full (ethanol is hygroscopic) and hopefully have a stabilizer that prevents two phase separation.

mtncat1 · Dec 23, 2018

NoNonsense said:
There is chemically no advantage to running lower octane fuel, including elevation and especially when boosted. You're either calibrating poorly or the lower octane fuel has ethanol content. There is literally zero evidence that can dispute this aside from people on the internet that don't understand fuel properties or thermodynamics giving their opinion.

you are wrong low octane fuel ignites easier than high octane fuel ,a low compression engine gains no advantage from high octane fuel and can loose power from running it,
however you are correct a high performance engine can gain massive amounts of hp by increasing compression and advancing timing .

NoNonsense · Dec 24, 2018

mtncat1 said:
you are wrong low octane fuel ignites easier than high octane fuel ,a low compression engine gains no advantage from high octane fuel and can loose power from running it,
however you are correct a high performance engine can gain massive amounts of hp by increasing compression and advancing timing .

If by ignite easier, you mean auto-ignite (knock) at a lower cylinder temp and pressure, then you are right. If you have a homogeneous charge and are controlling the ignition source (i.e. spark ignition engine), then you are wrong. Octane doesn’t effect flame propagation or flame speed / burn rate in the combustion chamber.

mtncat1 · Dec 24, 2018

any way you slice it there is no performance advantage in running high octane gas in a low compression engine .

kanedog · Dec 25, 2018

90% of you clowns can’t tell the difference between a good running sled and a stuttering, bogging sled anyways. As if you’re gonna know difference between 94 and 91 octane fuel. Haha

Mafesto · Dec 25, 2018

Ethanol contains less energy than non-ethanol gasoline. So if ethanol is the agent used to increase octane, lower performance could be expected.

Probably not to a level that would be noticeable.

Now the argument exists that higher octane would allow the compression ratio to be higher or timing advanced, thus noticeably increasing the power.

If we're simply talking premium vs 87 octane (neither containing ethanol) I'm not aware of a difference in btu content.

Teth-Air · Dec 25, 2018

I think you guys are missing the point some here as you argue over the fuels ability to burn one better than another. It's the maps that must be considered. Polaris says they have detuned the map for ethanol fuels in order to protect the motors. So if you run non-ethanol fuel you are giving up some performance by running the ethanol mode. Now how do they do this?? More fuel to keep the pistons cooler, timing changes etc. Maybe there are conditions that this ethanol map could actually make your sled run better though. e.g. I often have put my sled in ethanol mode for trail riding as I believe they run leaner at mid-range. Also if you have a more free-flow exhaust you may find a little richer fueling could even add power.

knikflyer · Dec 25, 2018

kanedog said:
90% of you clowns can’t tell the difference between a good running sled and a stuttering, bogging sled anyways. As if you’re gonna know difference between 94 and 91 octane fuel. Haha

Oh Great Oracle of all things sled, I believe it's called 'erring on the conservative side'. I'd much rather run a homebrew 94ish octane blend than the iffy pump I can buy here.

Sheetmetalfab · Dec 25, 2018

knikflyer said:
Oh Great Oracle of all things sled, I believe it's called 'erring on the conservative side'. I'd much rather run a homebrew 94ish octane blend than the iffy pump I can buy here.

Don’t feed the troll.

kanedog · Dec 25, 2018

knikflyer said:
Oh Great Oracle of all things sled, I believe it's called 'erring on the conservative side'. I'd much rather run a homebrew 94ish octane blend than the iffy pump I can buy here.

Ahahahaha! “Great Oracle of all things sled.” Thats awesome! I’m gonna put that under my screen name.

850 octane recommendations

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