I don't have to look it up, as I have been calculating the compression ratio on race engines and such for 40 plus years. It is a simple mathematical problem. Try it for yourself.

Example

Total volume at BDC = 1000cc
Total volume at TDC = 100cc
1000 divided by 100 = 10
Compression Ratio = 10:1

Next:

Total Volume at BDC = 990cc (Combustion area decreased by 10)
Total Volume at TDC = 90cc (See above)
990cc divided by 90cc = 11
Compression Ratio = 11:1

Math don't lie.....

http://en.wikipedia.org/wiki/Compression_ratio

AV8TOR