more power (higher compression ratio) and less gas to fill the chamber to make power..

if you want to make the same power and not be interference, from the conversions i understand, making the fully open valve measurement + 1mm as the tdc compression chamber you would be almost tripling the volume of the engine, so our 1.6 liters would need to be around 4.8 liters to make about the same hp with that drop in compression.

thats not factoring in all the other changes possible. but there are a reasons why a straight 8 out of the 30's only made like 50 hp..