Hey all,

Been trying for months to guess the true compression ratio of my built forged 3sgte without much luck...

Any of you guys know how to work this out if you dont know if the head been skimmed??

Given these specs I guestimated around 9.3:1

Ross 86.5mm 9.0:1 pistons
86mm eagle rods
1.0mm BG
50cc chamber (I've read)
- 4.9cc dome displacement (I've read)
1.360 piston height

Equates to 9.3 ish CR.

If the heads bin skimmed 0.2mm it jumps to 9.7 ish!!!

Does this sound about right?

180 psi on all cylinders cold. Stock is 160 psi (8.5/8.8cr)

St185 block with st205 head. 252 3sge/HKS 256 cams respectively.

Is it possible to find out an unknown CR with the engine in?

Could I do it with a manometer?

Any advice would be greatly appreciated... Again!

Thanks

Chris