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Superchargers Explained


Perfect Power Articles.


Superchargers are more predictable than turbo chargers. They were first used on V6 and V8 North American cars, but lately appear in European cars as well. The main reasons are the European road tax laws which tax the engines capacity. This note makes no attempt to explain the various superchargers (blowers) but to categorize them briefly:

•    "Wet" superchargers. Lubricated by the fuel.
•    "Dry" superchargers. Only air goes through them.

The Perfect Power fuel injection system works with both of them. The XMS4 Stand Alone range of products is recommended for engines up to 1600HP. For mildly charged engines (up to 0,5 bar, 7lb) with fuel injection already, the SMT6 or SMT8 piggy-back range of products is recommended.

All superchargers have two things in common: the engine drives them via a belt (or gears). They take a defined amount of engine power to operate. Two different types are used:

The air pump (roots) type: offering positive replacement. This is the most common one. Some are wet (lubricated with fuel), others are dry, and employ a seal, which requires no lubrication. They spin relatively slow, and always produce MORE air than the engine needs, thus providing always the same boost pressure. Theoretically, that is. At higher RPM they don't work that well, because aerodynamics and mechanical limitation restrict their operation. The throttle must be before the supercharger to restrict the airflow. This type of supercharger requires cast adapters to mount on the engine, and pulleys to set the boost pressure.

The windmill type: Like a turbocharger, spinning at high RPM's. This type is a relatively new development, because it requires gears or multiple pulleys to reach the relatively high operating speed. All these shafts require bearings and lubrication. Sometimes the gears make a noise. The boost pressure on these types is not constant, it increases with engine RPM, but loses efficiency at the top. An inter-cooler is sometimes used. The installation is relatively easy and requires simple engineering skills. They vary in size from an alternator to double its size.

All superchargers suffer from one ailment: they are difficult to control. The boost pressure is controlled by the pulley size and RPM. Compared to turbo chargers, they have a couple of advantages:

•    They produce very little heat in the engine compartment
•    They don't suffer from turbo lag
•    Each producer of air charging equipment swears on his product. Depending on the application, engine, and engineering available for each product, all have their place in the market, and work well if applied correctly

Most of the ‘windmill’ chargers have a centrifugal clutch. This clutch does not regulate the boost pressure, but prevents the gears from ‘rattling’. This arrangement requires some clever fuel tuning which can be performed with the XMS4 standalone systems, and with any of the following piggyback units: SMT8_3, SMT8L_3, and SMT8T_5.