BMW Supercharger Conversion

Most four-cylinder BMW owners will agree that these models are lacking in a little performance, largely due the weight that goes with the usual luxury appointments and BMW body strength.

US-based Downing/Atlanta, previously known for their Mazda MX5 supercharger conversions (as Sebring Superchargers), have developed a Supercharger kit for the Z3 and 1992 on 318.

Just as Mercedes-Benz have done with the SLK "Kompressor" roadster, by supercharging the lighter weight four-cylinder engine Downing/Atlanta have exceeded six cylinder performance levels and created a better balance vehicle.

A supercharger works similarly to a turbocharger in that it forces more air, and thus more fuel, into the engine. The difference between the two methods is that a turbocharger is driven by exhaust gasses whereas a supercharger runs off the engines crankshaft by belt. Thus a supercharger produces boost relative to engine speed as opposed to a turbo which often takes a second or two to 'spool up' before it creates sufficient boost.

The Downing/Atlanta supercharger kit looks right at home in the engine bay, and is engineered to factory standards. The installation of the kit involves replacement of the stock intake manifold. As no drilling or welding is required, the installation is completely reversible.

The supercharger is supported by the new manifold and by brackets that connect to the engine and chassis. Stock items like the oil filter and dipstick remain accessible. The fuel injection system is used unchanged except for the addition of a boost sensitive fuel pressure regulator.

A lot of thinking and development has gone into the conversion to suit the specific requirements of the BMW engine and owners.

The Downing/Atlanta kit uses a unique bypass feature that loops the supercharger output back into itself under part-throttle operation, effectively cutting off the supercharger. This maintains idle quality and highway fuel economy, while reducing engine loading. The bypass system greatly reduces the load on the engine and drivetrain as the supercharger produces power only when asked for with the accelerator pedal.

The kit also uniquely relocates the throttle upstream of the supercharger, ensuring consistent boost levels and ensuring driveability.

The manufacturers claim an increase in power of around fifty per cent. From the seat of the pants this seems to be spot on. Owners will be well advised to be very careful during the acclimatisation period. There are few other performance modifications that produce such an increase in power, and the first time you take the wheel of your freshly modified BMW you will think that it is a new car.

Acceleration is better than the six cylinder models and, with the linear boost of the supercharger, overtaking is a breeze.

Driven normally, fuel economy remains virtually identical to stock, an only if the supercharger is taken advantage of very regularly is there a significant penalty at the fuel bowser.

Speaking of fuel, premium unleaded is essential to prevent exposure to detonation.

Engine wear and longevity depend on how the car is driven and how it has been maintained. Simply having the ability to produce more power doesn't necessarily affect engine life. A more important consideration is maintenance.

The kit is generally compatible with other performance modifications like exhaust systems, but the makers do not recommend computer chips as they generally rely on advanced ignition timing which can cause detonation with the supercharger. Most strut braces will not interfere with the supercharger and its ancillaries.

Automatic models work very well with the supercharger kit, particularly in light of the increased low-end torque.

Downing/Atlanta have undertaken emission testing in America and the kit is "50 state legal". Therefore they expect no problems in any state of Australia.

Such a major performance modification would also need approval from your insurer.

Mona Vale (Sydney) based Barry Taylor Motors are bringing in the kits and offering a complete installation service. The upgrade can be performed in a day and, depending on the BMW model, costs around $7,500.

For further information contact Barry Taylor Motors.