low cr pistons, necessary?

[frostee]

hey there, if i were to go turbo with my h22, would low cr pistons really be necessary? I'm pretty sure they would, i dont really know why but the pros use them. Somebody told me that low cr pistons are for ricers because when you boost with them, the compression in the combustion chambers will go up anyways so no matter what, you end up w/ high compression, so how is it better running 8:1 cr pistons than 10:1 cr pistons with boost if it's kinda the same in the end??? just curious......

[gunnmen01]

OK think of this...8.0:1 pistons are like 11:1 CR underboost so 11:1 pistons under boost would be 14:1 CR under boost...im using random #'s i dont know what they might really be...but you get the idea i hope...


gunnmen01

[Polygon]

Like gunnmen01 said, that is true. Not exact, but true. If you don't use lower compression pistons you can crack your head pretty quick. A lot of pros don't lower their compression, but they are rebuilding their motors a lot. If it is a daily driver then NO QUESTION lower the CR to between 8.0:1 and 9.0:1.

[Neutrino]

i concur with polygon for a reliable daily driver never go higher than 9.0:1 compresion under boost. yeah pros use high compresion but they also use only racing fuel with very high octane amd they rebuild their engines all the time but they can afford it.

[frostee]

so is it faster when you just run high compression pistons under boost if you had the money to keep building it like some of the pros? or is it still the same if you just us low compression pistons and boost more?

[luti]

Can't you run high compression pistons with low boost safely?

[Neutrino]

Originally posted by frostee
so is it faster when you just run high compression pistons under boost if you had the money to keep building it like some of the pros? or is it still the same if you just us low compression pistons and boost more?

no high compresion and high boost result in faster speeds. I know a guy with a turbo b18 engine he runs around 11:0 with about 25-30 psi and he is in the 9's. But he rebuilds his engine all the time.

Originally posted by luti
Can't you run high compression pistons with low boost safely?

yeah wich is done all the time with slap on turbo kits on a lot of cars. A 6-8 psi is ussulally safe. But if you really want serious boost you have to rebulild the bottom end and lower the compression.