Just wondering. Like the Z400 and the 400EX. I know one of the advantages to the Z is that it is water cooled but why is that so much better? I also know that its a lot worse if you overheat a water cooled engine (head gasket blows etc.)

 

liquid cooled engines can rev higher and they make more power because of the less heat and higher revs.

 

Inside the motor, you have steel and aluminum parts working together. As they warm up, they have different expansions. the alum grows about twice as much per degree as the steel does. So if you water cool a motor, you can tighten up the clearance, because youll control the top temperature with the coolant. The more something expands at temperature, the more clearance you need at 68 degrees.
Also because of water cooling, the compression ratio can be bumped up more than if it was air cooled.