Whats the compression, with thinner headgasket?

I have a 2005 ZX6R (636) and i am going to be doing some work on her and after i get the cylinder head back will be using a thinner head gasket. .018 versus the standard .028 one.

Specs on Motor
Bore x stroke: 68 x 43.8mm
standard compression is 12.9 to 1
looking to get a nice and easy 13.5 to 1

 

Since the compression ratio is the ratio of the volume of the cylinder with the piston at BDC compared to the volume of the cylinder with the piston at TDC, to figure the volume, you'll need to know the volume of the combustion chamber with the stock gasket and the volume of the combustion chamber with the thinner gasket to compute the overall volume...

 

The calculation for compression ratio is:

(swept volume+clearance volume)/clearance volume

A down and dirty way (that's accurate) to figure clearance volume is:

Divide swept volume by 1 less than compression wanted.

Example: 149.945 / 11.4 = 13.153

Using 13.153 as the clearance volume, use the calculation above:

(149.945 + 13.153) / 13.153 = 12.4 ( supposed stock R6 compression ratio)

I used R6 numbers as an example above.
Of course, you're assuming the claimed stock compression ratio is really what Kawasaki says it is if you use their specs.

 

Online CR calculator:

http://www.csgnetwork.com/compcalc.html

more or less for cars, but works well for any engine. It does have the ability to adjust for head gasket thickness, as you requested, but you need to know your combustion chamber volume. Guess at about 12-13 ccs for a 600 and you can get an estimate if you don't have a burette.