Why no intercooler when it has a blower?

My understanding is compressed air fuel mixtures have an increase in heat and are therefore prone to detonation.

In this episode of Jay Leno's Garage at about 11:02 in the video they begin to discuss the new blown H2R. They mention how it does not have an intercooler.

How do they get away with putting a blower on this motorcycle and not having an intercooler to reduce heat for intake charge?

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  • I don't know the real answer, but relatively speaking, an intercooler is a newer add to super/turbocharged applications. It wasn't until very recently (last 20 years) an intercooler of any sort (air-to-water) was used on auto mounted superchargers. It isn't that an intercooler is absolutely needed, it's that it helps the intake charge be more dense and allows the engine to make more power. Apr 12, 2016 at 17:27
  • @Pᴀᴜʟsᴛᴇʀ2 : avoiding detonation is the main worry; the extra density is an added bonus mechanics.stackexchange.com/a/17491/675
    – Zaid
    Apr 12, 2016 at 19:38
  • 1
    @Zaid - All I can say is, intercoolers weren't a deal until the mid to late 80's. Blowers/turbos were successfully used well before that. I never said an intercooler isn't a bonus, which it is, just that it's not required for the forced induction to work correctly. Apr 12, 2016 at 20:28
  • @Pᴀᴜʟsᴛᴇʀ2 yup, agreed. Just wanted to highlight that the additional density isn't expected to be a whole lot.
    – Zaid
    Apr 12, 2016 at 20:33

4 Answers 4


So why are intercoolers used?

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.

    The result:

    • 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


The majority of heat generated during compression by a super or turbo charger is from the act of compression itself. Turbos are exhaust driven and will definitely be hotter but it is negligent compared to pressurizing the air 1 or 2 or more BAR. Intercoolers are as old as compressors themselves, they are not by any means new. They were used extensively in World War 2 in aircraft. Lower compression, proper fueling, and advanced materials and compressor design are in play here. But the most important bit in play here is the Dual Injection which essentially replaces the intercooler by injecting additional fuel At near TDC which cools the charge before pre detonation takes place. Cool with Fuel.


I own a 2015 H2 Ninja. One of the first things I discovered on the dyne was that the air filter cover caused a 25 HP reduction! Kawasaki also engineered in restrictions to fuel flow in top gear, so all I can surmise is they had to restrict the power one way or another, otherwise this stupid powerful bike would be even more powerful. An intercooler would have just added to this problem. As it is the motor backs off timing (and power) as it gets hotter. Hot intake temp = less power, cool it down by 100F and you have more power to deal with.


The real answer, even though these statements are correct, is that a super chsrger is engine driven, and not from an exhaust-side turbine that gets red hot in any number of youtube videos.

On a dragster, it is belt driven.

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