A blast from the past

The word "supercharger" is one of the most evocative in motoring vocabulary. No real knowledge of automotive technology is needed to associate it with a special type of power, and enthusiasts recall when supercharged machines from the likes of Alfa Romeo, Mercedes, Bentley and Bugatti ruled the Grand Prix roost.

Strong associations with yesterday's mile-eating thoroughbreds make one wonder why Britain's thriving outpost of the Mercedes-Benz empire - now the marque's third biggest market after Germany and America - has decided not to put a supercharger badge on the tail of the C230K saloon, Mercedes's first supercharged car for more than 50 years. According to one theory, the stodgy German equivalent, kompressor, is less likely to attract the attention of the police.

Jaguar and Aston Martin have launched supercharged cars in recent years, and Mercedes's decision to take the same route with this more affordable addition to the C-class range is another indication that the supercharger is making a comeback. The swift and stylish SLK two-seater will be available with the new engine when it goes on sale in Britain a year from now. Other models are in the pipeline.

All of which poses several questions. What does the supercharger do; what are its advantages; and how does it differ from the more familiar turbocharger?

Car buffs frequently refer to a supercharger as a "blower", because it blows air into the combustion chambers under pressure and increases efficiency to a remarkable extent. The supercharged Alfa Romeos that dominated Grand Prix racing after the Second World War had 1.5-litre engines whose 450bhp was about 10 times as much as the typical road-car engine of that size produced.

Thanks to its "blower", the new Mercedes saloon's four-cylinder, 2.3- litre engine provides exactly as much muscle (193bhp) as the C280 model's six-cylinder, 2.8-litre. But there is a distinct difference in the way the power is delivered. One of the supercharged engine's basic advantages is that it generates a lot of torque. So, for instance, the C230K is almost a second faster from zero to 60mph than the naturally aspirated C280. This appears to be a rare instance of getting something for nothing: increased performance is accompanied by the prospect of much lower fuel bills. According to the official test figures, the Kompressor is about 20 per cent more economical than its 2.8-litre stable-mate.

That is not the only good news, according to Dr Leopold Mikulic, the engineer in charge of developing Mercedes's petrol engines. Supercharging used to be regarded simply as a way to increase power, but now, he explains, "the supercharger is used for meeting contemporary demands such as lower exhaust emissions. In short, supercharging allows us to combine the economic efficiency of a four-cylinder engine with the power of a six-cylinder unit." This is partly because the C230K's catalytic converter gets up to full working temperature from a cold start more quickly. The engine beats the European test figure for carbon monoxide emissions by 70 per cent and for nitrogen oxide emissions by 20 per cent.

The supercharger's rival, the turbocharger, first became popular in the mid-1970s, initially thanks to Porsche and Saab. Its main drawback was "lag" (slow response). Serious power tended to arrive suddenly, because this type of "blower" is driven by gas-flow in the exhaust system. The supercharger has a direct link to the engine, so response is very much sharper.

The supercharging concept goes back to 1860, but credit for the first production car with a supercharged engine as standard goes to Daimler- Moteren-Gesellschaft - which became a part of Mercedes-Benz - in 1922.

Mercedes welcomed the new technology, creating a series of formidable racing and touring cars. Driven by the great Rudolf Caracciola, the relatively lightweight Mercedes SSKL packed a 300bhp punch and won three of 1931's big events. They included Italy's madcap Mille Miglia - a race contested over 1000 miles of public roads that were, in theory, closed to non-competing vehicles.

The C230K's state-of-the-art supercharger features two three-lobed rotors which compress air by spinning at up to 12,000rpm. My only complaint about this engine is that Mercedes was obliged to reduce the noise levels that have always been associated with superchargers. That makes sense from an environmental viewpoint, but eliminates the spine-tingling aural pleasure.

Prices for the C230K range from pounds 25,300 to pounds 28,400, depending on the level of equipment. Until the SLK sports car arrives in 1997, this is the nearest you can get to being a latter-day Caracciola. He was at the wheel in 1938, when a streamlined version of the supercharged Mercedes W125 grand prix car blasted along the Frankfurt-Darmstadt autobahn at 269mph. The new Kompressor is much slower than that, of course, but headlines as big as those that acclaimed Caracciola's record-breaking feat are guaranteed if you are caught exploiting its 143mph top speed in Britain.