Quote:
Originally Posted by arcturus
Just as a matter interest how does one work out how much to remove from a head to up CR? For example,if a head was skimmed to flatten it what effect would that have. How much would it need to be skimmed by to make a noticeable difference?
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To do a proper, but rough calculation, you need to do some measuring. I looked at the specifications of the B16B engine and there is not enough information given to determine. In particular, you need to measure your combustion chamber volume, the piston dish (or dome) volume, the piston to deck clearance and the head gasket clearance. Once you have the numbers from either the given specs and the measurements, you can plug the information into a compression ratio calculator. Then you can see how changes in the combustion chamber from changing the head affect the compression ratio.
http://www.csgnetwork.com/compcalc.html
Other major players in the compression ratio game are changes in piston dish (or dome) volume and piston to deck clearance. If you get real tricky and start using high lift camshafts, you may need to cut eyebrows for valve clearance in your block and that volume will also need to be calculated and plugged in.
I can't speak to the Volvo engines. My MGA engine has a somewhat smaller bore and a somewhat longer stroke than a B16B engine. The combustion chamber spec is 38 cc, but mine always seem to measure about 42 cc, probably due to valve recession and a slight modification (easing) of a point that creates a known hot spot. With those engines, each 0.010 milled off the head reduces the combustion chamber by about 1 cc and increases the compression ratio by about a tenth of a point. That should at least give a rough idea.
The stock B16B engine compression ratio is given at 8.2 to 1.