8 THINGS YOU NEED TO KNOW...

Motorcycle News (UK) - - Garage -

Types

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.

Feel

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.

Fit­ting one

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.

Gear­ing

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.

Drive­belts

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.

Bear­ings

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.

Pro­duc­tion charger

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’.

Main­te­nance

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.

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Procharger sys­tem uses gear­box to drive the im­peller

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