How to change compression ratio

[Redmachine]

I know I've searched but can't find the right answers. Without changing to a domed piston how do you change compression ratio's (increase). Naturally I have a 420a, and eventually I will be looking at a total rebuild, and no I am not looking to Turbocharge the car so don't answer with get a gs-t/gs-x. Any answers to my question will be greatly appreciated. My mods so far are 4-2-1 header with highflow cat, hp cyclone CAI, doing the cat back this weekend.

 

[miamieclipse]

umm go to howellautmotive, i think ure gonna need new pistons, not sure tho (howell automotive has 8:5:1, 10:5:1, and 12:5:1 i think). Lower is better for boost.

BTW what is better for nitrous?

 

[totaleklipse97]

well you don't HAVE to get new pistons for a higher compression ratio.. you have 2 other options that i know of. #1 if you are looking at a slight raise in compression then you can get a thinner copper head gasket and that will make a very slight difference. or #2 you can have the head "milled" to change the compression up to about 10.5:1 . For each 4 thousands you are looking at 0.1 point of compression so if your looking to go an even 10.0:1 then get your head milled 16 thousands. If you want it at 10.5:1 comression then you can have it milled about 35 thousands. I KNOW alot of guys here will say "we have no clearance heads" well that's bullshit, they may even call them "interference heads" but you have 40 thousands of clearance before the valve even gets into the valve seat in the piston. If you don't believe me look in the chiltons/haynes manual and it backs it up in writing. A guy on 2gnt has his milled 50 thousands.. i haven't talked to him so i don't know if he has any issues or not. Alot of guys have done this while changing their headgasket and im one of them i had mine milled 35 thousands and no problems. Easy and cheap way to raise your compression without changing your pistsons. And one good option is YOU CAN STILL BOOST... when you get lo-compression pistons it will just bring your compression back to stock. you can run stage 2 boost levels safely and up to about 12psi on race gas and things should be ok. Hope that helps you sir

 

[Redmachine]

Thank you very much that is exactly what I needed to hear

 

[totaleklipse97]

your welcome, anytime my dsm brotha. If you really want some great info.... check out www.2gnt.com it's been my home since day one! i don't know where i would be if i didn't find that site. Right now the registration is open, just e-mail the mods VERY nicely and they will probably let you in.