assuming the same fuel supply, would the air/fuel ratio get richer or leaner as compression is lowered? ...i am thinking richer...but what what the hell do i know...


[Modified by downpipe, 4:56 PM 1/31/2002]


[Modified by downpipe, 4:57 PM 1/31/2002]

 

Comparing an engine to an air pump, assuming volumetric efficiency remains the same, although there is more volume in the cylinder now, the engine may not be able to take advantage of it, so by that thinking it would remain the same. or, if the engine was able to fill the cylinder better (FI) it would become leaner. Wow. What a complicated question, this one really has me thinking. Another though, the cylinder having less compression, with the bottom of the combustion chamber(top of piston) being further from the top of the combustion chamber(cylinder head) I would think it would be a little tougher to maintain a more uniform mixture. Damn, all this thinking is hurting.

 

also, the lower compression would mean lower cylinder pressures, right? and what happens to the a/f mixture then when it burns? does it burn less fuel?

 

I'm guessing it would. My engine had bad rings, so my compression dropped alot .. and the car ran really rich. So I'm assuming it does burn up less gas.

 

You wouldnt have any higher cylinder pressures neccesarily, that is dictated by your timing, and of course detonation...which you dont want. I would say that you would run a little leaner with a lower compression ratio. Basically the reason you would need to run leaner is due to the fact that you need to "cool" the combustion chambers with higher compression, thereby running a little more fuel. There is also the need for more fuel with higher compression engines b/c the mixture burns much quicker than lower compression. Basically you can compare lowering your compression ratio like lowering the time it takes to burn the mixture, kinda like race gas.