8 THINGS YOU NEED TO KNOW...
There are three types of supercharger: centrifugal, roots and twin-screw. In theory, you can use any of them, but a centrifugal design is the only one that isn’t the size of a couple of breeze blocks, with a more rider-friendly performance. The two makes of centrifugal chargers that fit bikes reasonably well are Procharger and Rotrex. The Rotrex uses a planetary gearbox which uses the oil as a driving force in the charger, so needs an oil-cooling system. The Procharger has a gearbox to drive the impeller with an internal lubrication system.
One of the fallacies is that superchargers boost early. If you take into account the transmission losses and the fact the impeller needs to get up to speed to push air into the engine, they don’t boost much earlier than a well set-up turbo. It’s not a much quicker boost, but you do get linear power delivery. However, if you’re already up in the meat of the power curve, a supercharger has a faster acting throttle response. It feels more like a normally aspirated engine – when you rev it you feel it.
A supercharger can be fitted as long as it drives off the end of the crank or the drive system. Typically, the supercharger has a ‘clocking’ side (which way they rotate), so is fitted on the right-hand side of the crank. That’s the better side anyway, because they don’t protrude so much and the clutch/crank layout means the supercharger can be mounted securely with shorter belts and pulleys attached to the engine.
Unlike a turbo, a supercharger can be geared for a certain performance. If you know the engine’s peak rpm, pulley ratios and gear, you can work out the projected peak power.
These can be toothed or ribbed. Ribbed belts allow a degree of slippage, toothed don’t, which could be a problem if the engine or supercharger stalls at low revs and locks up.
The pulleys and bearings are outboard of the engine’s oil circulation architecture and spinning at 13-14,000rpm, so you need bearings to cope with the extra load. They are service items along with oil seals. A good rule of thumb for any tuned bike is if you double the power you should halve the service intervals.
The Kawasaki H2R’S unit is similar to the Rotrex design. What’s good about the Kawasaki is that it benefits from the Japanese firm’s multi-million pound R&D, with plenty of knock and ignition sensors. With aftermarket systems you have to stay in the ‘safe zone’.
A supercharger needs more looking after than a turbo. You have to monitor the tension of the belt – if it goes slack, you’ll get less boost per rpm and it will throw the fuelling out, making it run rich. If this is not spotted, the engine can end up running too lean when the belt is re-tensioned.