can someone please explain how the whole compression ratio thing works. i understand the higher the compression the greater the power but then you run into the risk of engine knock right. Also does a higher cr decrease gas mileage and how would you go about increasing the cr. thanks i feel noobish asking this.

 

Upon reading your question I became curious about this too and I found a pretty good article on it.
http://www.carcraft.com/techarticles...tio/index.html

 

Higher compression does generally make more power and torque however I have heard the gains stop at about 15 or 17:1. Well the engine is more prone to knock but can easily be fixed with an engine tune. You can increase compression by higher compression pistons, milling the head, thinner head gasket such as the y8. As far as gas mileage goes it depends.

 

also, with a higher compression ratio, you'll want to run premium gas, even with a tune. That's why you have to run premium on cars like the rsx-s... the general rule of thumb is premium for 10.5:1 and up.

 

i'm curious too. also why does everyone say you shouldn't run high comp pistons with boost. i see the logic behind it but wouldn't you just be able to lower the boost to run the same amount of hp?

 

that is a yes

 

If I'm correct, it has to do with detonation; it's just safer to run higher boost levels and lower compression. Still, with modern engines, you're fine to run moderately high compression ratios; Look through HMO's engine list; most of the compression ratios for the vtec engines are 10.4:1 - 10.6:1... those engines seem to do just fine with boost.