Building a performance engine
When it comes to building engines for all out performance for any application is for one is to look at the average rpm band the engine "see's" the most. Do you fire road ride, tight trail ride, round track, MX, drag, dune or simply a mix of all of the above. Make a decision on what fuel you want to run in the machine and base the compression of the build on that octane. For a build to be a success for the owner it needs to be better in most if not all areas than it was before, there is no reason for someone to run a large cam if the engine rarely revs over 6000rpm(limited by terrain not power curve).
Compression is simple really. Take your hand and put it over your mouth. With all of the air out of your mouth, use your tongue like a piston and try to draw air in. You will notice a vacuum will build instantly trying to get air through your mouth which is against your hand.
Now with your hand still over your mouth try this. With your mouth being half full of air do the same thing with your tongue. You will notice more delay of vacuum building in your mouth- the more air currently in there, moreso on the delay.
This is compression working on the intake stroke. The more compression you run in an engine the less "air" will be left in the chamber/cylinder after the previous exhaust stroke. With this then the higher the compression the faster the chamber/cylinder will pull vacuum and bring fresh air/fuel in. In return on this the fact the fresh air/fuel will be less contaminated by residual gas left over from the previous exhaust stroke the higher compression you run. The exhaust works better by removing more burned gases from the chamber/cylinder with higher compression and the intake has a faster recovery time on vacuum with less area in the chamber/cylinder to be filled at TDC.
Another thing about compression is also trying to be as effecient as possible at attaining it. Say you have an engine thats got a .040" thick head gasket, 60cc chamber volume, and the piston being .040" from the top of the cylinder at TDC and you have another engine with a .040" thick head gasket, 60cc chamber volume, and a piston being dead on .000" at the top at TDC. Both engines having the same static compression ratio which will make more power? The second engine because mainly the flame travel involved and the quench the second engine has by removing air/fuel as much as possible between the cylinder head deck and the top of the piston to get it into the chamber were it can be as close as possible to the spark plug. There will also be an advantage of having a smaller dome on the piston for flame travel and airflow across the piston.