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Hello all, well as the title says, what is the difference between 87 and 91 octane fuels? Does it actually make a difference for your sled/motor performance wise? reliability wise? Is it worth the extra $ at the pump to buy premium? On a few of my Polaris's, it has the premium/regular octane fuel key settings, what does this do? I have heard it messes with the timing?

And what is T.P.S? (Throttle Position Sensor right?) well if that true, what does it do or what is it's actual function?

Thanks in advance.
 

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87 and 91 are octane ratings, which essentially means that the higher the octane the better your sled performs. In sleds I always get the higher octane in my sled, but in a car it's worth going with the lowest, you do get better mileage but it isn't worth it money-wise. If you have the premium setting, run that with 91 or 93. It will make it run better, but don't do it with low grade fuel. Also, if you can find a gas station that doesn't put ethanol in their higher octane gas, then that would be even better.
 

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TPS, i believe is sense where you throttle is at so it know how much fuel/oil to send, is it EFI? otherwise it might be like a TSS which prevents you from starting your sled at WOT so it doesnt launch out of your hand, the higher the octane the more power, octane is what gives you more boom for your buck, the switch just changes your sled so it runs to perform better with the premium fuel
 

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do you mean fuel key as in the fuel resistor?

polaris' now comes with a feature where the ECU can select the proper operating software based on the type of fuel being used. i highly recommend running 91+ no matter what. but what the resistors are for is whether you are running fuel with ethanol or without. the 160 ohm resistor is for non ethanol. the 24 ohm resistor is for ethanol fuel. the 24 ohm is your best bet when in doubt of what fuel u are getting.

detonation sensors reduce the engines timing if the sled has bad fuel, water in fuel, plugged fuel filter, they dont recommend using and alcohol or de-icers like fuel additives while using the 160 ohm resistor.

they claim 87 is safe to use, but also claim u lose engine performance and fuel economy over all.

as far as the tps goes, its a sensor, sensors are only to do one thing, and that is relay info the sleds ecu. info on what the engine should do, provide more or less power, it helps make acceleration smoother, prevents bogging etc.

there are ways to test the tps, say if u think its faulty, polaris makes a kit for like 150 bucks but we made one in my dads shop, other wise go to radio shack and get the stuff u need for like 15 bucks
 

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the numbers are octane ratings. The higher the number, the harder it is for the fuel charge to ignite. With 87 Octane (Regular), if your sled motor is running hot (low snow condition, or just really "givin er" in low snow") the temperature is much higher in your motor. When a piston is on the upstroke with the fuel charge, the low grade fuel (87/Regular) can ignite from heat alone, not the spark from the spark plug, it ignites the fuel charge BEFORE it hits TDC and pushes down on the piston when it is still on the upstroke, causing a "knocking" effect, which after time (often a SHORT time) can melt or burn a hole in the top of your piston.

With 91 Octane fuel (Premium) the fuel doesn't really ignite due to heat if under heavy load in less than ideal conditions. It ignites once the spark plug produces the spark. You piston will rise all the way to TDC, and the fuel charge will burn when the piston is at TDC (assuming your timing is set properly). This DOES NOT make your fuel usage decrease or increase, just gets the most down pressure out of 1 fuel charge, and doesn't cause knocking, detonation or motor failure do to piston melting.

If your riding a liquid cooled sled, at average speeds on the trail, with cool temperatures and good snow/cooling, there is ZERO need for Premium fuel over Regular fuel, as it DOES NOT increase your performance or fuel milage.

Octane and the combustion of the fuel go hand in hand with engine temperature, pressure/load being exerted on the motor, and timing.

That is the reason Race Sleds use high octane fuels (104, 110, 114) as it is very susceptible to premature ignition, as the motors are very high revving and WOT the whole time for the most part, the motor is getting hot, and A LOT of load is being exerted onto the motor. The racers need the motor to ignite the fuel charge at TDC (or VERY VERY slightly before, to slow the momentum of the piston upstroke to invert into the downstroke) so the motor is burning all of the fuel charge (not letting some run out the exhaust port) and not putting a very heavy push on the piston trying to go in the opposite direction.

A LOT of piston damage (melting, pitting, warping, holes, etc...)are caused due to low octane's premature combustion. Most people say it is water in the gas that causes it. This is true, but not in the implied way. The water lowers the Octane level, which makes the motor blow the fuel charge on the upstroke, and puts too much pressure and heat on the piston.


Oh and a Quick tip, "Gas Line Anti-freeze" is just as bad as water (or worse) for lowering the Octane level of fuel, and they are, for lack of a better analogy, a bunch of little Pac-Man's. They need to eat something, and if there is no water in your gas, they go after the fuel molecules and particles which lower your octane. When using it, only use it if you really think water could have gotten in the tank, and only use A LITTLE!

No Idea with T.P.S other than it stands for Throttle Position Sensor.


**This comes directly from a chemist at Esso (my Uncle)**
 

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The only thing that octane in the fuel does is make it more resistant to detonation. You can run the engine with more timing and at a lower BSFC or (Brake Specific Fuel Consumption) if the engine does not detonate. Both will let the engine produce more power. A lower BSFC does mean it will have better fuel mileage weather it is a sled or a automobile.
The TPS lets the ECU know what the throttle position is. The ECU then adjusts the timing and the fuel delivery based on the throttle position (along with inputs from other sensors).
 

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erick said:
The only thing that octane in the fuel does is make it more resistant to detonation. You can run the engine with more timing and at a lower BSFC or (Brake Specific Fuel Consumption) if the engine does not detonate. Both will let the engine produce more power. A lower BSFC does mean it will have better fuel mileage weather it is a sled or a automobile.
The TPS lets the ECU know what the throttle position is. The ECU then adjusts the timing and the fuel delivery based on the throttle position (along with inputs from other sensors).
How does the T.P.S work on traditional style Carbureted motors though?
 

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It "feels" how far the throttle blade is open. This tells it how much air is coming in, and it sends a voltage signal ( up to 5 volts) to the computer. it sends signals back and forward so the ecu can adjust the timing accordingly.

you can get way more into it but im not the doctor in this area
 

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jesse500 said:
the numbers are octane ratings. The higher the number, the harder it is for the fuel charge to ignite. With 87 Octane (Regular), if your sled motor is running hot (low snow condition, or just really "givin er" in low snow") the temperature is much higher in your motor. When a piston is on the upstroke with the fuel charge, the low grade fuel (87/Regular) can ignite from heat alone, not the spark from the spark plug, it ignites the fuel charge BEFORE it hits TDC and pushes down on the piston when it is still on the upstroke, causing a "knocking" effect, which after time (often a SHORT time) can melt or burn a hole in the top of your piston.

With 91 Octane fuel (Premium) the fuel doesn't really ignite due to heat if under heavy load in less than ideal conditions. It ignites once the spark plug produces the spark. You piston will rise all the way to TDC, and the fuel charge will burn when the piston is at TDC (assuming your timing is set properly). This DOES NOT make your fuel usage decrease or increase, just gets the most down pressure out of 1 fuel charge, and doesn't cause knocking, detonation or motor failure do to piston melting.

If your riding a liquid cooled sled, at average speeds on the trail, with cool temperatures and good snow/cooling, there is ZERO need for Premium fuel over Regular fuel, as it DOES NOT increase your performance or fuel milage.

Octane and the combustion of the fuel go hand in hand with engine temperature, pressure/load being exerted on the motor, and timing.

That is the reason Race Sleds use high octane fuels (104, 110, 114) as it is very susceptible to premature ignition, as the motors are very high revving and WOT the whole time for the most part, the motor is getting hot, and A LOT of load is being exerted onto the motor. The racers need the motor to ignite the fuel charge at TDC (or VERY VERY slightly before, to slow the momentum of the piston upstroke to invert into the downstroke) so the motor is burning all of the fuel charge (not letting some run out the exhaust port) and not putting a very heavy push on the piston trying to go in the opposite direction.

A LOT of piston damage (melting, pitting, warping, holes, etc...)are caused due to low octane's premature combustion. Most people say it is water in the gas that causes it. This is true, but not in the implied way. The water lowers the Octane level, which makes the motor blow the fuel charge on the upstroke, and puts too much pressure and heat on the piston.


Oh and a Quick tip, "Gas Line Anti-freeze" is just as bad as water (or worse) for lowering the Octane level of fuel, and they are, for lack of a better analogy, a bunch of little Pac-Man's. They need to eat something, and if there is no water in your gas, they go after the fuel molecules and particles which lower your octane. When using it, only use it if you really think water could have gotten in the tank, and only use A LITTLE!

No Idea with T.P.S other than it stands for Throttle Position Sensor.


**This comes directly from a chemist at Esso (my Uncle)**
You are close, but you have a few details wrong after playing the telephone game with your Uncle.

The fuel charge is ALWAYS ignited before TDC. Race setup, trail setup, your Chevy Suburban, etc. The reason is that the fuel doesn't all burn at once. The flame kernel starts at the spark plug (assuming no pre-ignition happened - pre-ignition is what happens when the mixture ignites before the spark happens, and is quite rare unless you have way too tight of squish band), and then quickly expands to burn everything in the cylinder. The trick to spark timing is to time the spark so that the peak cylinder pressure happens as the piston starts it's downstroke after TDC. Detonation is what happens when the mixture burns fast enough that the peak cylinder pressure happens before the piston crosses TDC. It isn't necessarily because the mixture ignited before the spark plug ignited it. Detonation causes incredible heat on the piston as the temperature and pressure of the burn is extremely high, outside of normal tolerances for aluminum if it happens for any length of time.
 

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Bames said:
87 and 91 are octane ratings, which essentially means that the higher the octane the better your sled performs. In sleds I always get the higher octane in my sled, but in a car it's worth going with the lowest, you do get better mileage but it isn't worth it money-wise. If you have the premium setting, run that with 91 or 93. It will make it run better, but don't do it with low grade fuel. Also, if you can find a gas station that doesn't put ethanol in their higher octane gas, then that would be even better.
Hey, just wondering can you run regular 81 or 87 octane fuel in a 2007 Polaris IQ HO 600?
 

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81 octane? I don't think it's even legal to sell that.

87 is ok to run in your sled IF the manual says it's ok to do so.. If the manual says to use higher octane, than use higher octane.
 
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