Running the air through a supercharger is going to make it hot and detonation-prone. The primary benefit of an intercooler is that it reduces the temperature of the boosted intake air. This helps keep detonation in check.
The extra density is an added bonus because you can squeeze in more air to make Moar Power.
Does this mean Kawasaki defied physics with this bike?
Not really. They're just using other means to ensure that the risk of detonation is mitigated.
This is the press release which explains what they've done with the H2:
design the engine with a moderate compression ratio
8.5:1 is conservative, even for a forced-induction engine.
Since auto-ignition temperature increases as pressures decrease, Kawasaki are designing the engine to be such that the auto-ignition temperatures are far away from the engine's regular operating range.
rely on the fuel for charge-cooling
Evaporative cooling isn't new. It's useful to have liquid fuel absorb some of the heat in order to turn into fuel vapor. Given the elevated temperatures expected after running the air through the supercharger, there will be plenty of heat to do the job.
- vaporized fuel which is ready for combustion, and
- cooler air-fuel charge temperatures, which helps the engine operate away from the detonation-prone region
keep the engine cool
The idea here is to keep engine temperatures down. A liquid-cooled oil-cooler and high-cooling-capacity radiator help in this regard.
What's the benefit of avoiding an intercooler here?
Kawasaki may have gone down this road for the following reasons:
- weight savings
- space savings
- cost reduction
The first two are mentioned in the press release.
The latter is implied: no intercooler → no need to design → no need to buy