Just need some help in estimating compression ratios.

How much does the CR increase when the block and head get skimmed/rectified. Not that the head is warped, but because i'm going to be rebuilding it, it makes sense to do it to make sure everything is straight.
I'm guessing about 1/10th of a mm on the head and same on the block, so were looking at 2/10ths of a mm?

How much would that increase compression by?

 

Without doing the math, I'd say the difference will be negligible. I'll send you a PayPal invoice if you want me to do the math.

 

Negligible, maybe. But i still want to know.

 

2/10ths of a mm... Don't worry about it. That's only .0078".

 

The reason i ask is because i want to end up with a 9.5 CR, so i need to order the pistons with the right CR to allow for the rectifying.

 

The stroke is 81.4mm, and the bore is 95.5mm. Stock CR is10.6 to 1. You're removing a total of 0.2mm, which will reduce the volume of the combustion chamber.

You can use the formula here:
http://en.wikipedia.org/wiki/Compression_ratio#Formula

to solve for the volume of the stock chamber, since you know all the other values. Once you have that, you compute the volume represented by the 0.2mm change (volume equals piston area times 0.2mm), subtract that from the original chamber volume, and use the smaller chamber volume figure to compute the new compression ratio.

 

brings me back to my algebra days! time to shake the cobwebs.