There is also piston deck height, and piston dome height that has to be considered in the CR calculations. What the last poster stated would be accurate only for a completely flat top piston that had 0 deck height and no valve pockets, none which applies to the 10R, or most engines.
Years back I bought a graduated burret, can been seen in one of my threads. I used it to measure the combustion chamber volume of my ZX7 Superbike heads, and valve pockets on what I thought was 13 to 1 Wiseco pistons.
After I finished up the math, even with the 13 to 1 pistons I was only getting 11.5 to 1. So I called and talked to a tech at Wiseco. Here is what he told me.
Compression Ratios as advertised by the manufacters is as about inflated as the horsepower figures they advertise and the ZX7 really only had about a 10 to 1 Comp ratio stock from the factory, so I was actually getting a 1.5 bump with the Wiseco pistons. Which is significant, but no where near 13 ro 1 as advertised.
He says they (Wiseco) obviously can't advertise the pistons as 11.5 to 1 because that would be less than what Kawasaki claims for the stock engine. They would never sell any pistons and are therfore forced to play the same game of inflating #s.
So not only are HP #s inflated, so are claimed compression ratio figures.
Unless you have a graduated burret, a piston deck height measuring tool, know for certain or can measure the dome volume of the piston and the valve pockets, you will never get an accurate reading.
My guess stock is less than 12 to 1. and the .45 gasket don't really bump it up much more than a 1/4, if that much.
I know this is hard to beleive, but I have measured many engines and have found it to be so.
Also consider 13.00 to 1 is the max compression ratio that NASCAR allows and they have the most effiecient heads and piston domes ever designed, and detonation is the limiting factor for HP because they are only allowed 100 Octane gas.
So NO, we do not have 13 to 1 CR in our engines, even with the .45 gasket. It would NEVER run even on 93 pump gas and stay together at 13 to 1.
Last edited by JimmyJam; 12-24-2007 at 05:37 PM.