BY CHRIS HARRIS | 21st May 2007
The new five-door VW Golf GT TSI is powered by a revolutionary new petrol engine that is both supercharged and turbocharged to produce sportscar performance combined with mini-car fuel economy.
Unlike most new technology that arrives via upper-end luxury models, the new twin-charge Volkswagen is available at an affordable $34,990 – just $2000 more than a regular 2.0-litre Golf FSI and some $5000 cheaper than the five-door Golf GTI 2.0-litre turbo.
With a capacity of just 1.4 litres, the new TSI (Twincharger Stratified Injection) engine develops some 125kW of power and an astonishing 240Nm of torque, running on premium-unleaded petrol.
It has the sort of performance you might expect from an engine with twice its capacity while returning average fuel consumption of only 7.7L/100km. And it already meets EuroV emission standards.
With the standard six-speed manual gearbox fitted, the Golf GT TSI accelerates from 0-100km/h in a claimed 7.9 seconds. With the optional ($2300) six-speed DSG self-shifter, that time comes down to 7.7 seconds.
Secret to the TSI engine’s success is its unique combining of a supercharger with a turbocharger.
Without getting too technical, this is what makes it work so well: Turbocharged engines use exhaust gas pressure to drive a turbine that then forces more cool air into the engine, therefore increasing the power of the combustion.
However, the downside of turbos has always been lag – the delay in getting that power surge because of the time taken between hitting the accelerator and the exhaust pressure building to produce the power surge.
Supercharged engines have no such lag because a supercharger is driven directly off the crankshaft and is therefore already running at speed when you hit the accelerator, so the boost is right there immediately.
Low-down performance and response of a supercharged engine is therefore superior (despite some power drain because it runs off the crankshaft), while the turbo really comes into its own at higher revs, producing power essentially for free.
Enter the VW TSI twincharge engine.
It is basically a turbocharged engine that uses a supercharger to pump air into the turbocharger at low revs (up to about 2400rpm). The turbo consequently spools up in a fraction of the time than for a regular turbo engine, delivering almost instant power at all engine speeds.
The supercharger kicks in at up to 3500rpm, but after that the turbo can effectively work alone.
When the supercharger is not in use, it is disengaged by an innovative VW-developed magnetic clutch so that there is no unnecessary load on the crankshaft.
In practice, then, the TSI engine has the instant throttle response of a supercharged engine and the power of a turbocharged engine – but when you are cruising it has the fuel consumption of a normal “atmospheric” engine, which is only 1.4 litres in the Golf GT.
While a turbocharger alone operates at up to about 1.3 bar pressure, the TSI runs at a maximum of 2.5 bar at 1500rpm.
With the supercharger alone delivering some 1.8 bar of pressure at just above engine idle speed, low-speed response is remarkable. At just 1250rpm, the 1.4-litre engine already produces some 200Nm of torque.
Maximum torque of 240Nm is delivered across a diesel-like band of 1750-4500rpm.
Being based on the VW’s EA111 modular engine and using an equally well-proven Roots-style Eton supercharger, the new TSI twincharger engine had little trouble meeting VW’s durability requirements, according to TSI project manager Niels Moeller, who flew out from Germany for the launch.
Mr Moeller said there are no plans employ TSI technology on bigger engines, claiming that the natural torque of bigger engines makes it less advantageous, but it is easy to see the potential for the full range of petrol engines in these fuel-conscious days.
Some European countries have tax concessions for cars up to 1.4-litre, which is why VW chose that capacity, but we can still imagine a future 2.0-litre TSI with the performance of a large-capacity V6, or even a 3.2-litre V6 TSI capable of thrashing most V8s on the market. But we shouldn’t get ahead of ourselves…
VW has grown considerably in recent years in Australia, even moving into the Top 10 sales chart, driven by a diesel engine strategy. Now the company wants more petrol engine sales and sees TSI as another good reason for people to look at the brand.
An initial batch of only 420 Golf GT TSIs has been imported, but this is not a limited edition model. If there is demand, VW can supply as many GTs as the market requires.
Golf GT TSI specifications are essentially the same as the Golf FSI, which means you get dual front and side airbags, curtain airbags front and rear, ABS anti-lock brakes with EBD and brake assist, front and rear fog lamps, remote central locking, electronic stability control, 17-inch alloy wheels, dual-zone climate control, automatic mirrors and wipers, cruise control, heated side mirrors, height and lumbar front seat adjustment, trip computer, chillable glovebox and power windows.
It has the same suspension tune as the GTI and therefore sits 15mm lower than regular Golfs, but VW Australia does not believe it will eat into sales of the GTI – which, remarkably, is the top-selling Golf model in this country.
“GTI buyers buy the whole package, so we don’t think it will be affected by the GT,” VW Australia managing director Jutta Dierks told GoAuto.
“We think the market will be those people who want all the performance benefits of a turbo-diesel but who don’t want a diesel. We have to gets customers from other brands.”
This new Golf was to have been called the GT 1.4 TSI, but local executives decided to drop the 1.4 so late that it was already printed on promotional banners and the press kit cover.
Understandably, they want people to focus on its deserved GT status rather than its rather misleading capacity until such time as people recognise the significance of the TSI badge.