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[jdmart]

on my celica i have a few mods and my cuisn tweaked with the timming a little bit and if u know what im talking bout the timming was set at 16 and it used to be at 5 and i noticed it gave it a lil more power and it kinda sounds a lil like its "caming". but it drives better and i have not noticed any problems at all..
what do u guys think about this i would like ur info......

[6strngs]

I'm taking college classes with a major in automotive technology. One class I took last semester was titled "Fuel induction and emissions" in which we talked about gasoline and all the gasses that come out the tail pipe and what they are and how they get there. We covered timing, and the properties of gasoline in that class. I'm sure that higher octanes burn slower. But, what I mean by burns slower does not mean better gas milage. it burns slower in the combustion chamber giving it a better resistance to knock.

Peak pressure, or the point where the pressure in the combustion chamber becomes the greatest to where it forces the piston down, thus spinning the crank, thus moving the other pistons and keeping the car running, should be around 10-20 degrees After top dead center (ATDC). Now, gasoline takes a few milliseconds to burn (approx 2-3 mS) so you fire the spark plug before the piston reaches top dead center (BTDC) so that a few mS later when the piston is on it's way down, the explosion actually occurs. Imagine pedalling a bicycle, when the pedal comes up and around you wait until it's a little bit past the top and then push down on it with your foot and it gives you propulsion. now, if you were to step on the pedal when it was already halfway through it's trip down, you wouldn't get as much power as if you stepped on it right as it passed the top mark. That's how advancing the timing gives you power. However, fire the spark plug too soon and the explosion will happen too soon happen while the piston is still on it's way up and make it hard for the piston to complete it's revolution. That's knock. at idle, we could get away with advanced timing, but as you drive, your timing is always changing, and sometimes under high load, such as wide open throttle, it'll be so advanced it'll begin to knock, which is why we use higher octane gas. This way the gasoline takes longer to burn and preventing knock by delaying the peak pressure slightly.

That said, I don't really see how a higher octane gas could give you worse gas milage. except maybe because it burns slower, it doesn't give as complete of a burn because it's doesn't have enough time to finish, and so more of it just gets wasted out the tailpipe, but that's the only thing I can think of.