due to longer stroke, stroker pistons not only have repositioned wrist pin (higher up) but also more dish volume. CR is calculated as a ratio of total cyl volume at lowest piston point (BDC) and at TDC. Since strokers have longer stroke, the cyl volume at BDC is higher, and the TDC volume needs to be greater if you want to maintain the CR. SInce head and head gasket volume is usually the same between stroker and non stroker engines (depending on the bore) the only way to increase TDC volume is trough greater dish in the piston. If you take a look at the piston spec for various pistons you wil see that stroker pistons have greater dish volume than non stroker ones for the same CR.

Long rod pistons need to have piston pin height from the stroker piston but dish volume from a non stroker piston. For example, in my long rod 2.0 build I am using 10.5 CR stroker pistons which in 88mm crank non stroker application with 156 mm rods will give me roughly 9.4CR

 

Correct.

As a quick rule, all else being equal, one can expect a drop in SCR of ~1 full integer from using a piston intended for a 2.3 in a 2.0, such as from 9.5 to 8.5:1.

 

Stroker pistons have a different dome dish because changing the stroke alters the compression ratio...

 

boost leak?

 

i tested up to 22psi with no leaking and took forever to loose pressure. my tester popped off at 22psi LOL.
i'm doing a leak down tonight, but i don't think that's the issue. my compression is perfectly even all the way across. i'm doing it anyway.

i expect the compression to be a bit lower after i have done some research. it appears the pistons are 8.5:1 and i am running a 264 cam. the idle and power loss at me stumped.

my next idea is unrelated to the pistons: it's to pull the MIVEC gear to make sure it was put on correctly. if it's off, that explains the idle, loss of power, and slight compression loss.