In an ideal world, the more 'squash' you get the more bang you get for your buck.

You either do this via raising the compression ratio, or adding a means of forced induction, like a turbo or supercharger, both of which force more air into the cylinders.

If you still don't follow, think of an apple press, the more you squash them the more you get out, so you can either ram them in (akin to forced induction engines) or squash the loose apples harder...

The compression ratio is the amount of loose apples you start with, say 9 vs the amount of space for apples when the piston is at the top of its stroke, say 1. In this example you would have a CR of 9:1.

Does that help?

Tom