c/r

[yelizardking]

what exactly is the compression ratio? can i get some info on that? why is it so very importan?

[94_AcCoRd_EX]

Compression ratio is the ratio of the total volume of the cylinder and combustion chamber with the piston at BDC (bottom dead center) and TDC (top dead center)...

[yelizardking]

can you run that by me one more time?

[AzCivic]

ok when the piston is at the bottom of the stroke(BDC) that is the 1 in the compression ratio ex. 9:(1) and when it reaches the top of the stroke(TDC) that air is compressed 9 times smaller than it original volume hence the 9 in 9:1 . the higher the compression ratio the more power there is to be had but you'll also risk detonation(the air and gas self igniting at a bad time) which will ruin an engine unless you run race gas which has a higher octane(higher octane= more resistance to detonation).
On the street 11:1 is as high as you want to go, but with a turbo you'll want a 8.5:1 or so compression. Hope this helps.

[Mushroom]

Why do we use lower compression with FI?

[AzCivic]

a turbo forces more air into the cylinder so in a way it increases compression plus the if your intercooler sucks then the intake charge will be hella hot and again give you another chance for detonation.