DD......checked out Tech Wiki for measuring cc's on the cylinder head and piston. Didn't have a metric syringe handy.....measured 1 oz (29.57cc) for the GX combustion chamber and 1/2 oz (14.79cc) for the A15 piston dish. How do I calculate compression ratio?

I like to google for a compression ratio calculator

Figure your head gasket thickness
* 1.2 mm standard gasket
* 0.6 mm high perf Nissan gasket
* 0.8 mm Tomei gasket

Your parts sound fairly typical, I'm gonna guess 9:1, good for regular fuel

CR=Vc/(Vc+Vs)
Vc = clearance volume 1.5oz in your case
Vs = swept volume = stroke x cylinder area

Just be consistent with units and you can use what ever units you want.

am I doing it wrong? Says 8:1. That'll run like a dog ...

Piston dish may be too much

Might need more help with this. Do I need flattop pistons? I will remeasure today.

By your calcs

Swept volume plus c/c volume (head only) plus gasket divided by chamber volume (piston and head) plus gasket

A15 = 371.75cc per cylinder
Chamber 29.57 + 14.79 = 44.36
Assume 1mm gasket = 4.5cc

So 371.75+4.5+29.57 = 405.82 divided by 44.36+4.5

= 8.3 cr

I just plugged the figures into this calculator:
http://www.csgnetwork.com/compcalc.html
and got 8.44 CR using the above figures.

This is why i used the mazda flat top pistons when i did my rebuild, though it seems i ended up with too much CR....
Use the mazda pistons but machine off 1.5mm rather than 1mm and it should be about 10.5:1 CR

Ok thanks everyone. I will get a more precise syringe tomorrow and check the cc's again. Will report back later.

There are at least 5 different factory A15 pistons, all with different dishes. Because A-series heads are all around 30cc, the dish is used to vary compression from USA 8:1 and 8.5:1 to JDM 9:1

* Centered dish shallow
* Centered dish deep
* Offset dish

Also the shape varies to correspond the chamber design. The Offset pistons enable some quench without flattops. The H95 head is the only one with a larger chamber CC, so uses the smallest piston dish.

DD...I have the offset dish and the engine came with the H95 head which I will replace with the GX head. So if I use a centered dish piston will my compression go up?