By EWAN KENNEDY  in Wolfsburg
2 October 2006

A fascinating new engine design from Volkswagen has turned conventional engineering wisdom on its head. Because this is an engine with the power, torque and smoothness of a 3.0-litre six-cylinder unit, but the economy of a typical 1.6-litre four-cylinder. Emissions are generally even lower than those from a 1.6 engine.

Put another way, VW has introduced a petrol engine with the characteristics of a turbo-diesel, but without the disadvantages of noise, vibration and low-rev range of the diesel.

Tagged the TSI Twincharger, this petrol engine uses both a supercharger and turbocharger to boost its performance. The supercharger pumps more air into the engine at low revs, the turbo at higher revs. Both can operate at the same time in mid range, with the engine’s management computer selecting the degree of co-operation required between the two. When not being worked hard the engine runs without either the supercharger or turbocharger.

The supercharger only works until 2500 rpm under normal circumstances, but can provide boost as high as 3500 revs. Unlike most superchargers, the TSI's unit is disengaged when it’s not required. This means it’s not robbing the engine of any power. Just as importantly the supercharger can run at a faster speed when it is operating and thus provide more than normal boost.

Complicated? Yes, it is rather. But it certainly appears to be well engineered in the typical German manner and there's no reason to believe it won’t last as long as any other engine. The complication is therefore of no real concern.

Expensive? Not really, because the basic engine is considerably smaller than a V6 that would provide similar performance and therefore cheaper to manufacture. It’s also less complex than a V6 as the Twincharger has no need for balance shafts and doesn’t require complex variations in valve and intake-tract timing.

We have deliberately said nothing about the capacity of the new VW engine until now to avoid preconceptions. At only 1.4 litres it is apparently a tiny engine, but it produces a respectable 125 kilowatts. And a more than respectable 240 Newton metres – that peak figure running all the way from 1750 rpm to 4500 rpm. In other words, many drivers will spend virtually all their time with the engine running at its peak torque figure for maximum efficiency.

We have enjoyed a 600 km introductory test drive of the Twincharger engine in a new Golf model called the Golf GT.

A high speed blast, to be perfectly honest, on the famed German autobahns. We saw up to 220 km/h on the speedo, though we generally ran the GT with the normal traffic flow in the range of 160 to 80 km/h.

(No, we didn’t crash, it’s only in the imaginations of some so-called road safety experts in Australia that cars mysteriously spear out of control once they reach 111 km/h.)

Autobahn dashes were interspersed with interesting cross country work. Yet the average fuel consumption was a mere 8.9 litres per hundred kilometres despite the hard use. A V6 petrol engine may have used about 30 per cent more fuel, and created 30 per cent more emissions, under the same circumstances.

The VW Twincharger engine is beautifully refined, smooth and very willing to rev, other benefits achieved by its small capacity.

It has a huge range of useable revs. From 1500 rpm all the way to 7000 rpm it pulls eagerly without a touch of fuss. If you pay attention you can just hear and feel the supercharger clicking into play. There was no turbo lag as the supercharger works to help the engine get up to turbo speeds.

To get similar economy and low emissions as the Twincharger you would have to buy a turbo-diesel engine. But even the best of these aren't as smooth as a petrol unit. And turbo-diesels have an irritating habit of running out of puff at about 4500 rpm, just at the point where they are really starting to come on strong.

Will we see the VW Golf GT with the Twincharger engine in Australia? Almost certainly yes, probably in the third quarter of 2007. Price has yet to be established, in Germany the Golf GT costs about 10 per cent less than the $39,990 Golf GTI that’s already on sale in Australia. However, the Australian Golf GT would be likely to have a different specification to the model sold in Germany so our local price may vary from that 10 per cent number.