oil

[Black Yaris]

Originally Posted by Spades

[/threadjack] (again)

High octane rating only determines at what point the fuel will combust. A high octane fuel is to prevent a thing called "Predetonation" from occurring.
Predetonation is not a term you ussually hear in parking lots full of kids showing off their cars, ussually it is used at the dragstrip listening to guys talk about their 400+HP 4cyl boosted cars.

Predetonation is what happens when due to pressure in the combustion chamber the fuel ignites prematurely before the spark plug triggers. This is a very bad thing, because if the number 1 cyl predetonates, it goes against the crankshaft being turned by the pistons that are firing in the correct order with their spark plugs.

The force inside a cylinder chamber becomes increasingly higher when you try to force 20 PSI of boost into it. When the piston goes on what is called the compression stroke(the stroke where it mashes the mixture of air and gasoline together in preporation to be ignited) the pressure can sometimes be enough to cause the mixture to explode.

High octane rated fuel is used to prevent the gasoline and air mixture from blowing up before it is supposed to. The only benifit to using high octane fuel on a car that was designed for 87 octane piss water is that it sometimes burns cleaner because some gas stations may put more adatives in it and sometimes it is a slightly better grade of fuel.

If you ever get boosted or change the compression to something radical(say 14 to 1) then look into 89 octane, untill then, feel free to waste your cash on the gas that costs 30 cents more a gallon.

we had this debate a long time ago... just do a thread search to see what realy happens... our car CAN tell the difference between octanes and does get better gas miles with higher octane