tech overview

supercharging motorcycles

Similar to Turbocharging but instead of using exhaust gas pressure to drive impellers that then force feeds the engine induction; it uses the rotating speed of the crankshaft to drive a supercharger via belt / gears.

As the rpm of the engine increases so does the supercharger impeller increases in speed & thus boost increases. The amount of boost created therefore is directly relevant to the engine speed. Due to the size issue certain types of supercharger are not suitable for motorcycle application.

These tend to be the traditional Roots, Screw & whipple type. For compactness motorcycles have found the use of turbo style impellers driven by a gearbox a more compact design that fits easier onto a smaller bike engine.

There are several brands of aftermarket Supercharger available for use on motorcycles for example Procharger, Rotrex & Vortex to name but a few. Kawasaki have even introduced a range of factory supercharged motorcycles using a gear driven impeller. Their performance is very curtailed in stock form though offering room for good performance gains.

to debunk one myth

From our testing none of these styles of supercharger will create more low down power than an equivalent turbo. The reason is simple. There is the relevant losses of driving the supercharger to take into account but also the impeller needs to reach a certain speed from which it can give positive pressure.

A good Supercharged engine feels & acts like a much larger capacity aspirated engine. The throttle response is instant & more predictable & linear than a turbo. This is because the Supercharger is creating boost by the revs of the engine & not by the load of the throttle. This means it is creating boost on slow acceleration & fast acceleration & on a constant cruise & even on a deceleration if the rpm is high enough. This also makes the dump valve more aggressive during closed throttle in getting rid of the excess pressure. In turn though due to the superchargers nature it builds up a lot more heat than an equivalent turbo & will consume a lot more fuel than a turbo as the enrichened boosted area in the fuel map is much larger. So the instant throttle response comes at a price. More maintenance is typically needed in the belts & pulleys & associated bearings. A loose or slipping belt would loose boost & in turn power & make the map go rich.

Also be aware a supercharger will not create the same HP or Torque of a Turbo at the same boost pressure on an engine. Still the instant throttle response & with it boost on demand is addictive & makes for a great road bike or specific race application.

Big CC Racing do not recommend the use of superchargers on 1000cc motorcycle engines & below due to the poor return in power levels & performance against cost comparisons.

Big CC Racing have chosen the use of Procharger Superchargers over other brands for several reasons Firstly their direct drive gearbox has no slippage unlike the Rotrex which uses traction oil that can overheat. In turn it has no need for an oil cooling system with oil header tank etc making install on a motorcycle much easier.

The biggest factor in choosing Procharger is the horsepower return per psi of boost is just so much higher. At 10 psi pressure a Procharger with its advanced design billet wheel impellers creates 20 to 25 hp more than any equivalent Rotrex we have tested on our dyno.

chargecooling & supercharging

Is available with Supercharged applications & will deliver a power increase through the reduction of heat into the engine. Be aware that typically using the same pulleys you will experience a reduction in boost pressure. This is because the inlet air temp has fallen & in turn the pressure as the cooler air is not so expanded. 10 psi boost with a good chargecooler would typically become 7-8psi boost. This in turn helps reduce dynamic compression. A turbo by comparison would still make the same boost but more power still as the boost is controlled by the wastegate & it would self correct the air flow.

Typically a chargecooler works by using water to cool the boost down in a radiator style matrix. The boost travels through the fins & the water travels through the water tubes cooling the fins down . That water would then need a radiator or ice tank to dissipate the heat into & a water pump & hoses etc to complete the package.

variable boost control

Is also available on Supercharged applications which Big CC have been able to do on custom installations for race customers. Something our competitors are yet to catch up on. We also have experience for race customers in spraying nitrous with supercharged applications. Be aware again max boost is determined not by the controller but by the rpm & the pulley ratios. The boost controller would unlike a turbo act in a manner to reduce the boost & bleed it off. We offer 2 stage & multistage boost options.

what power level can i get?

The power potentials of your Supercharger package depends on many factors.

• The Supercharger’s claimed power potential by the manufacturer at max impeller rpm (not always accurate especially in motorcycle applications)
• The Superchargers systems actual potential. This is not the same as above as restrictions may exist in the fuel system such as pump or injector size or filter flow rate etc or the air flow through intercoolers, airboxes air filters etc. Big CC always try to match the systems abilities to that of the supercharger to enable all scenarios for a customer.
• The engine type. Certain engines can only handle a certain amount of power. Think about the loading per con rod in the power you seek to realise easier the stress certain engines like 2 or 3 cylinder motors may be under compared to 4 cylinder etc.
• The engine work carried out to strengthen your engine. Using stronger conrods special low compression forged pistons, stronger & larger engine studs/bolts etc power potentials can be dramatically increased.
• Fuel type. Boost pressure dynamically increases the compression ratio of an engine. Super unleaded fuel reaches its limit before 14:1 with forced induction especially with the increase in air inlet temperature. So it is important for you to find from your supercharger system supplier & tuner what your boost limit is on regular pump fuel & also what the limit is on high octane racing fuels.
• The air inlet temperature. Running air to air intercoolers or liquid to air chargecoolers will reduce air inlet temperature which in turn will help prevent detonation. The size of the turbo will also determine air inlet temp as larger superchargers will move more air with less heat & less exhaust back pressure. Added bonus of colder air is more power for the same impeller speed as the air is denser. A supercharger fitted with intercooling would expect its boost pressure to drop slightly as the denser air after the cooler drops the air pressure on the boost gauge/inlet of engine.
• The tuning. Work carried out in so far as keeping the engine safe such as enriched air fuel ratio & ignition timing etc.

A simple example: A Supercharger system non intercooled could run 10psi boost = 250hp max on pump fuel with the same pulleys & a chargecooler fitted it could drop to 8psi boost yet make 270hp. Compression & tuning of ignition & fuel A/F will equally give variances.

So when asking what power your bike will make it depends upon the package that you can afford to go with in so far as engine compression & strength, turbo size & turbo system choice intercooled or not & the safety of the tuning work. Big CC Racing are happy to go in depth with you to help select your best package available for your budget.

ok what is involved price wise?

There are 4 main cost factors to supercharging a bike. They are as follows….

• The type & choice of Supercharger system that fits your needs. We offer several stages from basic street use to full blown drag or land speed.
• The engine work required to sustain your power level you want reliably. Inc removal strip inspect modify rebuild & refit etc. The choice of vehicle you have & the power you want will determine the mods required to achieve reliability in your application.
• The installation & Dyno . The cost including bracketry welding mods & other modifications to the vehicle required & a full rolling road set up.
• Electronics & other ancillaries. This may be power commanders or Stand alone ecu’s, boost controllers, full exhausts instead of dumps, scavenge pumps, oil cooler / radiator upgrades, lock up clutches & so on. Not all bikes need them but some do & your application will determine your options or requirements.