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)**