[Christ]

The turbo has a dual benefit - it reduces pumping losses, and makes use of excess heat from the combustion cycle, which would otherwise have been wasted as noise from the exhaust.

The compression issue, I don't fully grasp, myself. I know that there is a limit to comp enhancement, where it just takes more energy than it's worth. Diminishing returns and such. Basically, its a mater of heat and ratios.

Heat, in that you have enough heat for total combustion of the mixture AT THE RIGHT TIME.

RATIOS: mechanical advantage, pure and simple. The more leverage produced, the more energy is transfered to the crank shaft. Increasing comp can achieve this, because it changes the ratio of induced volume to compressed volume. However, it takes energy to compress air and fuel, and there is a point of diminishing returns.