The formula your suggesting will only give the difference the change in the gasket thickness will make. If I am understanding you correct, then you are correct.JimmyJam, the equation that I gave is accurate as long as you are changing the compression by changing the head gasket thickness only. Piston domes and valve pockets have absolutely no bearing, because you are physically moving the entire cylinder head (valves and chamber and all) closer to the top of the piston by the difference in thickness of the head gasket.
I wouldn't be surprised one bit if the compression ratio is not what they claim it is.
I tried that B4, far to much monkey motion involved. So I graduated up to how real engine builders do it using a graduated burret and a piece of plexiglass with a hole in it. The piece of plexi glass is placed over the Combustion Chamber and sealed with grease. Then it is filled thru the hole.I think that Gofaster´s formula is correct.
No matter the piston dome shape, the cylinder holes of the gasket are about circular. That holes form a cylinder itself, the height (thickness) of the gasket.
As the .45 gasket is .2 thinner than the stock gasket (Kawi numbers..) you can calculate a .2mm height cylinder, and subtract it from the theorical combustion chamber volume.
Then you make this calculation independent from the piston dome shape.
If you want to know the exact (real) comb. chamber volume, then you may find the exact TDC in any cylinder, and fill the chamber up with oil, using a syringe until the oil begins to reach the plugs thread. Be carefull to record the amount of oil exactly. Cylinder bank has to be as 90° to the floor as possible to minimize the possibility of keeping an air bubble in the chamber.
You can take the oil out using the same syringe and a hose.
but will not account for the shape of the top of the piston, (All piston manufacters such as Wiseco / JE have this figure and can give it to you, or you can measure it your self using a berret, a piston, the block and piece of plexi glass like I have shown.)If I'm understanding that method correctly, the flat piece of plexiglass gets laid against the cylinder head with the engine apart. It will give the volume inside the head itself, but will not account for the shape of the top of the piston, the distance from the top of the piston to the top of the block, or the thickness accounted for by the compressed head gasket. And obviously the engine needs to be apart. (Or is that piece of plexiglass going somewhere else?)
The other method thru the sparkplug hole works with the engine assembled and accounts for all of the above. Yeah, it's a pain one way or the other, but something like the burette/syringe method is the only way of measuring the ACTUAL volumes of these chambers.