Centrifugal vs Roots Supercharger
datboimell said:
what is the difference between the centrifical and roots sc's..................i just need to kno these things................ :hal:
Any supercharger is belt driven. But, they fall into two broad catagories: Centrifugal or Roots. Think of a Roots supercharger, inside the housing as two screws that spin in opposite directions creating higher intake manifold air pressure. It is said to be a "positive displacement" type system. In other words, it makes your engine seem "bigger" in terms of total displacement than it actually is. The Roots type system usually combines the blower and intake manifold in a combined housing. The OE's use that alot, for example, the Mustang Cobra comes from the factory with a roots type of blower, so did the Ford LIghtining.
The other system is more like a turnbine system, a housing that is round and circular, that does not replace the existing intake manifold. It usually sits on an adapter plate and is driven by the serpentine belts like any other accessory system, looking like a turbo in fact, but simply belt driven, not exhaust gas driven. It actually forces a higher volume air into the motor, as a whole. Now that air is hot air, and high pressure air. If you remember basic physics, as pressure rises, so does temperature, but volume drops. P/V=T, or Boyles Law.
The system is not self sealed. It typically requires a hole be made inside the oil pan, so that the same engine oil that cools your motor also cools the blower.
What you must always keep in mind, is that with more air, you need more gas and more spark. You want to maintain the same "stoichemetric" ratio of 14.7:1, that is roughly speaking, 15 parts air to one part fuel. So, since the air increased as a result of the turbo or supercharger, so too should the fuel. So, you'll need bigger injectors, with a higher flow rate. You will also need to make the spark plugs one degree "colder" than stock. Your ECU however, is programmed for the stock amount of air, which is atmospheric pressure, not above atomspheric pressure, to maintain the right air-to-fuel ratio. So, your injectors could be bigger, you can have a supercharger or turbo, but your computer brain must tell it the right air-to-fuel ratio, or a have a reprogrammed "map" between "closed loop" operation, or part throttle, vs WOT (Wide Open Throttle) or "open loop" operation.
The nice thing about the Stillen system, is that they did all the engineering for you. THey put together the right ratio of air, fuel, spark and so forth, and all you're doing is buying it. Stillen has deep connections to Nissan, since he was a factory race car driver for them. It's as close to a "nissan-made" supercharger system as you can get.
Remember,the Nissan motor is high compression motor, about 10:1 compression ratio. To avoid knock, most motors that rely on a power adder likewise get to be rebuilt with a lower compression, such as 8:1. However, you're keeping the guts, or the lower end, the same. With that said, you can not stuff too much air into the motor and the PSI you can put into the motor is limited by the fact that you're not lowering the compression ratio.
So your ability to produce power with either a turbo or a blower is really limited by the fact that you're not rebuilding the motor to be lower compression, but simply adding a power adder. Your motor has to be in FANTASTIC shape before you do this. Make sure you do a compression check and a "leak-down" test before this work is done to the motor, or you will NOT have a motor.
Good luck. Alex
