How does tunning work?

[quyen]

I have noticed that it is possible to tune an engine to produce different amount of power (e.g. Standard M5 engine 400bhp, Tuned M5 engine in Ascari 500bhp). How does this work and what are the advantages and disadvantages of tuning for more power?

Edited by quyen on Friday 25th April 08:14

[quyen]

Thanks Jon for the succint answer. I guess I should have guessed that from basic physics (no such thing as free energy). However, I have always been intrigued as to why when an engine can achieve 500bhp, a company like BMW only put it out at 400bhp. Must be something to do with the cost of tuning it up to that spec I suppose?