About compression ratio evo-help me

[flanker c]

hi guys,i am not mloc fans.last year i bought mitsubishi evo4 transplant with evo6 engine done by previous owner.after 8 month used in boost0.9bar i plan to do top overhaul and minor mod.after my mechanic take out the engine head, he said my engine not a stock! piston change already..87mm size! probably Fairlady VG30DETT piston.also 1.5mm HKS metal gasket.intercooler and cams from TME.Turbo from E7 (TD05HRA-16G6-9.8T)..after overhaul completed my compression ratio only 7.8:1 ! isit too low for 4G63 engine? i dyno it and only can gain 271.1hp on wheel..boost 1.4 bar run with PFC Commander and 255lph walbro fp. the question is what the best compression ratio for evo engine? i got feel more G force and I curiously why my HP like stock engine? How to gain compression ratio? all evo sifus pls help me??

 

[Cow]

correct me if i'm wrong, but the 1.5mm gasket probably lowered the compression?

 

[sub7]

I have similar setup and intend to boost high. That's why the compression is lower than factory 9:1. You should get more power with 272 cam :)