If increased performance is desired, one can 'port' the engine, to increase the intake and the exhaust duration.
Cleaning up the bypasses and the crankshaft gas passage, would increase the gas flow.

Increasing the blow-down period would make a tuned exhaust system more effective.

Dropping the head would increase the compression ratio and minimize the squish clearance.

As you can see, the sky is the limit and then there are carburettors and tuned pipes and... and...