The compression ratio is swept volume + clearance volume divided by clearance volume.
The swept volume is the amount of volume take due to one stroke of the piston.
The clearance volume is the gap that is left on the top of the piston at top dead centre. This gap comprises of the head volume and the rest of the cylinder and the head gasket.
So if you reduce the gap on the top of the piston by skimming the head, the swept volume will be forced into a smaller space, thus increasing total pressure.
If the compression ratio tops 10.5/1, then you may need to start using fuel additives to prevent detonation.
Increased pressure means higher temperatures before ignition. So the total temperature during and after ignition will be higher than normal. The temperature increase may go high enough to cause spontanious combustion, (explosion) rather than a regulated burn. This can cause significant damage to the pistons, valves and if too severe, the head itself. Look on youtube at drag racing and you will find some footage of cylinder heads being blown off or apart due to extreme pressures within the combustion chamber.
For my next lecture, we will be going into the pro's and cons of nitrous charging!
