How to Maintain a Supercharger for Longevity

Popularised for motorcars in post-war North America, superchargers for cars are types of air compressors that extract more power from an engine. The more air that is present within the engine's combustion chambers, the more oxygen is available to be burnt. Logically, therefore, if extra fuel is added, greater power outputs will result.

Engine superchargers tend to be driven mechanically by the engine. While this more detailed technical blog looks at the practical issues covering superchargers, this one examines the theoretical aspects. This information may help you, should you be looking to buy a supercharged car, seek to repair one, or even modify an engine to accept forced induction.

You will find three main types of superchargers. The differences depend on how the air is moved from the atmosphere and into the engine intake.

THE ROOTS STYLE SUPERCHARGER

The Roots-style supercharger is the most common and oldest type of unit. It employs counter-rotating meshed rotors to pump air into the engine. While being the least expensive supercharger to manufacture, it is relatively inefficient, due to the excessive quantity of waste heat that it produces.

The resultant temperatures reduce the air's density, curtailing the engine's power output. Even an air-to-air intercooler may not be able to cool the air sufficiently to compensate.

Despite this, the Eaton Group of North America has refined the Roots supercharger and car manufacturers have adopted them. One of the main changes was a subtle helical twist made to the internal rotors. This type of supercharger is called the 'Modified Roots'.

You can find these superchargers on a variety of cars, from small performance engines to large capacity units, powering luxury vehicles. For instance, the fourth

generation of the Eaton Group’s smallest supercharger, the M45, was fitted by BMW to the pre-2006 MINI Cooper S. Some versions of this car were fitted with the 5th generation M45, the rotors of which were treated with an Abradable Powder Coat (APC) instead of an epoxy layer.

This change was to reduce the internal tolerances to boost efficiency. Yet, Eaton's TVS (Twin Vortices Series) supercharger is used on larger vehicles.

Perhaps the most common examples on UK roads are 5.0-litre versions of various Jaguars and Range Rover models. Despite the TVS series being more advanced and refined, it remains a Roots-style supercharger at heart.

THE TWIN-SCREW SUPERCHARGER

Taking advantage of an expired German patent from 1878, the twin-screw supercharger was developed first in the mid-20th century by Alf Lysholm, a Swedish engineer. Instead of using rotors, a set of worm gears mesh together.

This draws air into the supercharger and, as the taper within the gears reduces in size, the air pockets shrink. This compresses the air, prior to it being expelled from the supercharger and into the engine intake.

Unlike the Roots alternative, the inlet and outlet sides of a twin-screw unit are airtight. Not only does this result in less heat being produced but twin-screws also require less power to operate, compared to Roots superchargers. Yet, this efficiency comes at a cost.

A twin-screw supercharger kit is significantly more expensive to manufacture, which may explain why it tends not to be offered by car manufacturers, although you may find it in specialist aftermarket applications, or conversion kits.

ARE SUPERCHARGERS BETTER THAN TURBOCHARGERS?

A turbocharger is a type of engine supercharger. It performs the same task as a mechanically driven supercharger but it works very differently.

Instead of being driven by the engine, the turbocharger is powered by exhaust gases. By utilising energy that would have been wasted otherwise, turbochargers tend to be more efficient than superchargers that are driven mechanically. They are

also relatively inexpensive, which explains why they dominate the market, compared to engine-driven superchargers.

Even so, turbochargers struggle to perform at low engine speeds. Therefore, modern developments, including variable-vane and geometry technology, have been introduced to solve these failings. You can find twin-charged cars, which are fitted with a supercharger for low engine speeds and turbochargers for higher RPMs.

Turbocharger operating temperatures tend to be extremely high, which places extra demands on the car's cooling and lubrication systems before supercharger servicing, as well as the unit's internal bearings. For these reasons, check out this blog for advice on turbochargers.

HOW DOES A SUPERCHARGER AFFECT FUEL ECONOMY?

You may be wondering "how long does a supercharger last?". As superchargers tend to be fitted to large-capacity, or high-performance engines, fuel economy tends to be less of an ownership priority. Like almost every engine, much depends on how it is driven. Should full use be made of the performance available, fuel economy will be worse than a car that is driven relatively sedately.

ARE THERE ELECTRIC SUPERCHARGERS?

While most superchargers are driven directly by the engine, electric superchargers are powered by an electric motor. As this limits mechanical drag on the engine, electric superchargers are more efficient. Audi's SQ7, Bentley Bentayga and tesla supercharger are typical production cars that are equipped with an electric car supercharger.

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