Clever folk, those Germans. While the Japanese are seeking fuel efficiency through hybrid, electric and hydrogen options, the Germans have found it by combining turbo and supercharging.
This isn’t the ultimate answer of course. The TSi engine still uses fossil fuels and thus
is a short-term response, but an innovative one which at first seems contradictory.
After all, forced induction is normally associated with high performance, and allied to it is an insatiable appetite for fuel.
What makes it work here is vastly increasing the performance potential of a small engine.
It’s a similar principle to hybrids, which use an electric motor to offer higher performance than expected from a small engine, enabling a 1.3-litre to adequately power a small/medium-sized car.
VW’s TSi system does the same, and better – at 125kW and 240Nm there’s more than enough power on offer from the 1.4-litre unit to not just propel this Golf, but to give it a hooligan nature. Yet if you’re a petrolhead, you’ll have switched off at 1.4, and therein lies VW NZ’s problem. How to get Kiwis in the driver seat, feeling the power, not the lack of cubic inches.
Despite the lack of engine capacity, there’s plenty of automotive boasting on offer from this car.
TSi project manager Niels Muller starts the bidding with his tale of a 1.2-litre, 147kW TSi engine in a Polo.
“I got to 255km/h on the autobahn – and with Polo suspension you had to be a little bit brave to do that. One day a BMW 535 came up behind and indicated I should pull over. He followed me to 230, 240, and he had no more chance.”
Joking? Nope. Try this new Golf GT. Fire it up, plant boot and it’s a rocket-ship, a sensible shopping hatch on P. For that 240Nm of torque is available anywhere from 1750rpm to 4500, not far below the 125kW power peak. All that torque for so much of the rev range makes a powerful punch in any language, but particularly in a car this size. Diesels are renowned for their torque, yet the 1.4 diesel now launched in the Polo only manages 180Nm.
So how do they do it? Put very simply, both turbochargers and superchargers supply air under pressure to the engine, to increase combustion efficiency – thus offering more power from any given unit.
But because a turbocharger’s turbine is driven by exhaust gases, it doesn’t operate until the engine’s already turning over at a fair rate of knots. Below that optimum rpm, there’s not much on offer, hence turbo lag, the period of ordinary drive before a turbocharger’s boost comes in.
But a supercharger actively drives the air, so it can work at lower revs. The combination that VW has harnessed uses a belt-driven Eaton supercharger at lower revs, to boost performance before the Borg-Warner turbocharger cuts in.
Better yet, here the exhaust gases are circulated back through the system to ensure unburned fuel is recycled. It’s a very busy little unit. At low revs the supercharger comes into play; from 2400 to 3500 both super and turbochargers operate with thesupercharger deactivated via a magnetic clutch at 3500rpm.
The change-over is seamless. Meanwhile airflow is carefully controlled, at times going through the turbocharger twice.
The system involves temperatures higher than 1000 degrees. “Volvo’s five-cylinder turbo and the little Smart go that high in temperature, but both companies have problems with cooling,” Muller says.
This one doesn’t, thanks to some very complicated plumbing. “You can drive 211km/h for extended periods without using any fuel for cooling, which assists good fuel consumption even at high speed.”
It all sounds simple, but the technology required to combine the super and turbocharging, along with the direct injection that raises the compression ratio, makes for very high pressures within the system.
“Boost pressure is 2.5 bar,” Muller says. “Effective pressure is 1.5 over atmosphere, higher than Porsche’s 911 turbo which has only 1.1 bar of boost pressure.” But what about the soundtrack? “An Eaton supercharger or Rootes blower can sound like a jet plane – 160dBa is possible – and we had to reduce that,” says Muller. “(In) the first TSi cars, the supercharger dominated everything.”
Not now. Placing the supercharger low, behind the engine and beneath the driver’s level, helps; as does strategic placement of covers.
The result is this level of performance – Muller says 67 percent more power and 82 percent more torque than from a conventional engine of the same capacity, combined with a claimed 7.2 litres/100km fuel consumption in the Golf GT, and low emissions.
This achievement, combined with the level of reliability and longevity, won VW’s TSi the 2006 international engine of the year award.
Demo cars are touring New Zealand now, with stock arriving in January. The GT slots in just below the hot GTi hatch, and will sell for $47,990.
What next? Well, once punters get used to the idea that a small engine can produce oodles of power, we’ll get even smaller capacity versions, with a bit less power than this one and lower thirst. After all, TSi isn’t designed for sporting applications. It’s meant to bring reduced fuel use with good driving behaviour.
VW would eventually like to take it to bigger cars, and to other fuels. It’s working on TSi with CNG, which will first be fitted to a Passat.Other new VWs come as something of an anti-climax after this stuff.
But launched in the shadow of this giant-killing technology came more from the German brand – the $26,990 diesel Polo; the $31,990 CrossPolo, a mildly SUV-styled 2WD hatch that will appeal to city slicker style-seekers; and the Eos – a rather handsome convertible with an electrically folding hardtop roof, and driven by a 2.0 T-FSI engine, at $53,990, or by the soon-to-arrive 3.2 V6 from the Golf R32 hot hatch.