Supercharger produces more energy

By T Uncle

Supercharge! The concept of utilizing one form of energy to enhance another is one that has fascinated mechanical engineers for a long time.

It is used in four-wheel drive or limited-slip differential systems, for example, where hydrodynamics and normal mechanical operations are combined to create the commonly used viscous coupling.

Just as familiar is the turbocharger.

This device harnesses the spent energy contained in an engine's exhaust gases to enhance the combustion process and increase both power and, more importantly, torque.

It is, in a sense, "free" energy, although in reality, a turbo asks for some small price to be paid.

This is usually -- by comparison with a similar-size, normally aspirated engine -- in terms of absolute drivability and overall fuel economy.

However turbo technology has matured to the point today where the pitfalls of the past are minimized to the extent that they are no longer a real problem.

However, a concept similar to turbocharging has been running along parallel paths for an even longer time.

This is the supercharger, a mechanical device perhaps better associated with drag racing than road, or even racing cars.

In essence, there is not a lot of difference in the effects turbocharging and supercharging have on an internal combustion engine.

The basic intention is the same: cram as much fuel-air mix into the engine's combustion chambers as possible to increase the intensity of the explosive process that produces the power that drives the crankshaft that drives the wheels.

Both systems are basically pumping devices that draw air into the engine, compress it, then force-feed it through the inlet ports where it is mixed with fuel before passing into the combustion chamber to be ignited.

The denser the charge, the more energy produced.

The difference between the turbocharger and the supercharger is the method used to drive the turbine that compresses the inlet charge: the turbo uses the gases flowing through the exhaust to do this, while the supercharger is driven by pulleys, or gears, attached to the engine.

The effects on engine efficiency are not difficult to imagine. Where the turbo really only suffers a slight increase of back pressure as a result of the gases being slowed down as the force their way past the turbine, the supercharger imposes an extra mechanical load on the engine, similar to that created by a power-steering pump or air-conditioning compressor.

This robs a portion of the extra power produced by the supercharger. However there are advantages too.

Perhaps the most significant is that, unlike a turbocharger, a supercharger is able to provide its inlet boost almost from the moment the engine starts spinning.

Depending on the gearing used to drive the supercharger, it can be running at full boost not long after the engine passes idling speed.

So the "lag" factor, minimized though it may be in modern turbo engines, is virtually nonexistent.

A supercharged engine can quite literally behave as if it has a much larger capacity at all operating speeds.

And, unlike a turbocharger, it is not as prone to developing the under-hood heat that is a byproduct of its being driven by extremely hot exhaust gases.

However, despite the fact that supercharging has a long history, going right back to the early days of the automobile, it has never quite gained the respectability of the turbo.

Perhaps this is something to do with the fact that installing a supercharger is, by nature, a more complicated task than installing a turbo.

It needs to be driven by the same system that motivates various ancillaries, including the power steering, or the alternator, and ideally, should be an integral part of the engine.

The turbo more or less is simply attached to the exhaust system, downstream of the manifold, and is more easily adapted to any engine configuration.

This is the basic reason why a booming after-market turbocharger industry developed in many countries during the 1980s.

Supercharging, for road use, has been treated rather more cautiously, although today it is starting to come out of the closet.

Supercharging has a certain cachet simply not enjoyed by turbocharging so, for the time being, most of the highly visible supercharged cars belong to the upper end of the market.

Cars such as the Jaguar XJR, or even the Miller Cycle Mazda Eunos 800 -- which uses a variation of the supercharger system in that a clever variable cylinder head valving arrangement manipulates the conventional four-stroke cycle to supposedly improve efficiency -- are putting supercharging to effective use without overly flaunting it.

Like turbocharging, supercharging has benefited from modern metallurgy and vastly improved engine management so that its benefits are being exploited more and more effectively.

Maybe it will supplant the turbo one day.

Or maybe, the turbo will continue to keep a step ahead because of its simpler, easier application and the fact that engineers are generally more familiar with it.

Whatever, anything that has the potential to improve the efficiency and performance of an internal combustion engine is worth persevering with. And both turbocharging and supercharging are capable of doing that.