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My supercharged K8 project...

131758 Views 192 Replies 85 Participants Last post by  D.Man

The bike pictured above is my bone stock K8. A friend gave me a fantastic deal on this bike last year, and it has just under 2000 miles on the clock. I love this bike for the same reasons everyone does -- incredibly smooth, extremely capable and controllable, great power, and fantastic ergonomics for a supersport machine. The local Dynojet 250i says it puts down 152whp (SAE corrected), which is actually more power than a full-exhaust, PCIII-tuned '04 ZX-10R produced on the same dyno.

Now, normally the next step would be to add an exhaust, change the gearing around, or add some braided lines, and while I'll eventually get to those mods, I have something different in mind right now...

It's a Rotrex C15-60 supercharger, right off the plane from Denmark. This little unit can support over 230whp, and that's the number I'll be shooting for with my little project here. Also, the impeller wheel used to be cast, but these new wheels are apparently machined out of billet.

Before you ask, yes, I am a power junkie. There's just no going back once you've ridden a boosted literbike...

You can see how small it actually is compared to the bike. Somehow, some way, it will fit in there...

After staring at this sight for a couple of days, I realized the only place to put this thing is in-between the engine and the radiator, just below the frame. I'd love to stick it up higher, but the frame would get in the way of the belt (which is a dealbreaker) and the radiator fan would also have to be relocated. Placing it lower eliminates these problems, but makes it much harder to hide the drive behind the fairings and also places the inlet of the Rotrex very close to the header. I also do not want cornering clearance to be compromised at all, so it will be in as far (and up as high) as possible.

If anyone is wondering how I plan on driving this thing, take a look at the picture above. The M10 bolt currently fastened into the end of the crank will be removed and a machined adapter will take its place (this adapter has to locate perfectly off the crankshaft for this to work). A pulley will sit on top of this adapter and then drive the supercharger via an 8mm synchronous belt. The supercharger bracket will either take the place of the stock cast cover or locate off of it -- I'm not exactly sure yet which way to go.

There's a lot of work left to be done, but I'm looking forward to it. I plan on tuning the ECU directly and, of course, it will run on pump gas. In the meantime, wish me luck, and stay tuned...
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With where the supercharger has to be placed, you could have went with a really, nice, small turbocharger and not worried about heat soaking the living hell out of compressor side.

A centi super will come up a lot more controllable, but one thing you're going to have to keep in consideration is the amount of revs versus the pulley you're going to be running.


Not to mention the amount of cyl pressure a supercharger adds versus a turbo. With a smaller turbo you probably could have ran a non intercooled set up, been reliable, and made the power you are aiming for at a lot safer cyl pressures. Superchargers make some SERIOUS heat.

Granted this isn't a roots style blower, but still, I take it a uber rich AFR will be your means of intercooling or are you aiming to run an air-air set up?

:lol not to mention a by-pass system to keep surge under control.

Very interested.

Good luck.
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Steddy, this is not my first Rotrex-equipped bike. I've been personally running my stock-internal, non-intercooled, pump-gas powered VFR on 10.5psi since '07 without a single issue to speak of. As you said, tuning is key, but the boost curve of a centrifugal supercharger is just about as good as you can get for running safely on pump gas. This bike won't be pushing that amount of boost, but I do plan on it maxing out the C15-60.

I will be utilizing a vacuum operated Bosch bypass valve to limit surge. To tame the exhaust heat, I plan on wrapping the entire unit with Thermotec shielding, and also plan on running a separate oil cooler for the Rotrex itself.

You just cannot beat the tuning benefits and controllability that a supercharger provides, and though it can be tricky to implement, I love the challenge (and, of course, the end result).

Hey I wasn't a doubter by any stretch of the imagination...more curious than anything. Forced induction on a motorcycle engine isn't overly common, unless the thing is a straight drag bike USUALLY.

Can't wait to see the finished project
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