I am having trouble figuring the cr with various D series pistons for my ZC turbo project. I would like the cr to be 8.8:1 to 9.0:1 and use off the shelf pistons, any brand really. I've been using the cr calculator from
http://www.c-speedracing.com/howto/c...c/compcalc.php
and using these #'s

ZC bore 75mm
ZC stroke 90mm
cc volume 43.8
piston to deck height .040
stock head gasket

Every piston dome displacement I put in is giving me what I think are really low #'s. Like a SRP D16Z6 piston that is 9.1:1 on the Z6 coming up with 7.3:1 or a SRP D16A6 piston rated at 11:1 on the A6 coming out to 9.4:1 on the ZC. I realize the ZC has a bigger cc volume...but my #'s seem way low. Any ideas where my math is wrong?

And concerning using Endyne rollerwaves for the ZC do they all require the block to be .5 overbored unless you custom order them?
Just thought I'd ask that question here first.

 

You are doing everything right, putting a6 pistons in a ZC will give you incredibly low compression.. its because of the large chamber.

Factory ZC pistons are domed....

I cant remember what sizes the rollerwaves come in, but the largest is .20 over and that is what I got, I dont know if they have stock bore size, they could have a few mm larger ones.

Jeff