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Click to view picture gallery“Choosing between
  a petrol or diesel
  engine for your new
  VW Golf is not easy.
  Both offer a lot of
  benefits. Now VW has
  made it easy for you,
  with the new TSI engine
amazingly, really
offer the best of
  both worlds...”

THE HOLY GRAIL for auto-motive manufacturers struggling to meet lower and lower emission targets, while at the same time retaining the performance that customers still demand, is to combine the benefits that petrol and diesel power plants currently offer in
one affordable engine.

What is needed is an engine that is smooth and quiet (as found with petrol power) combined with high torque at low engine speeds for quality of driving, flexibility, responsiveness and fuel economy with low emissions, as found in the latest direct-injection diesels.

Step forward VW's new TSI technology, as seen on its latest 1.4-litre direct-injection petrol engine dual-charged with a supercharger
and turbocharger. This technology has been tried before but not successfully. Other manufacturers could not make the change from supercharged power to turbocharged power seamless.

The European CO2 emissions target for a manufacturer's overall range of passenger cars by 2008 is an average 140g/km. Whilst the latest generation of direct-injection diesel engines are well on their way to reaching these strict levels, petrol engines are not.

Volkswagen says that the new targets must be met, but not at the expense of driving pleasure. Consequently, they are working on
the most effective way to reduce consumption and CO2 emissions by downsizing in capacity with new powerplants that are compact, durable and suitable for mass production. However, smaller engines
are not renowned for giving good driving performance and that is something customers insist upon, otherwise they will not buy them.

As its core, TSI uses a 1.4-litre FSI engine which is then dual-charged through a combination of an engine-driven supercharger operating at five times crankshaft speed and an exhaust gas turbocharger, arranged in series.

The result is improved driving characteristics over those of the current FSI units. The belt-driven supercharger operates at lower engine speeds, with the turbocharger coming in as engine speed increases to create a seamless progression from one source of boosted power to the other. In the mid-range at the changeover point, the blown air from the supercharger is diverted into the turbocharger for a short period before the turbocharger takes over completely. This 'series' pro-cess is continuous and a sealed-for-life clutch allows the supercharger to switch in and out automatically on demand.

Volkswagen says this arrangement provides excellent driveability and performance throughout the range, with high maximum torque but no turbo lag. It combines the particular benefits of both petrol and diesel engines: petrol characteristics are low noise and vibration; diesel qualities are good driveability, high torque from low engine speeds and fuel economy.

Key to the TSI's success is that direct-injection allows an abnormally high compression ratio of 10:1 to be used in conjunction with high maximum boost pressure of up to 2.5 bar. Together, this enables the relatively small engine to use very high gearing to provide improved
fuel efficiency for a petrol engine, particularly at motorway cruising speeds. As an additional bonus, the TSI engine produces high power and torque across a very broad rev range — from 1,000 to 6,500rpm.

The new TSI engine has a capacity of 1.4-litres and is available with the choice of two power outputs: 140 or 168bhp. The 168bhp version has the same peak power as a conventional 2.3-litre petrol unit but with 20 per cent lower fuel consumption, returning 38.2 mpg on the combined cycle. It also produces maximum torque of 177lbs ft from 1,750 through to 4,500rpm.

Depending on the specific model and power output, the 1.4 TSI units return between 37.7 and 39.2mpg with CO2 emissions of between 169 and 180 g/km. The new 1.4-litre TSI engine replaces, in some VW models, the current 148bhp 2.0-litre FSI engine.

All TSI engines drive through a manual six-speed gearbox. A DSG auto-matic option is also available with the 168bhp engine. Later in the year this will also be offered with the 139bhp unit.

TSI technology has already received international acclaim, having been named Best New Engine of 2006 in the International Engine of the Year Awards. It also won the 1-litre to 1.4-litre category.

Volkswagen's Golf is one of the first models in the VW line-up to benefit from TSI technology. It is available in Sport and GT trim with 139
and 168bhp respectively. TSI 139bhp engines are also available in the Touran and Golf Plus. Volkswagen says the compact engine has been designed for eventual use in other model ranges such as the Polo, Passat and in the new Eos coupé-cabriolet ranges once supplies of the new unit become more widely available. In the future it is also likely that TSI engines will be used in the other Volkswagen family brands such as Audi, Seat and Skoda.

TSI prices start at £15,995 for the Golf Sport 139bhp three-door model. The Golf GT 168bhp three-door costs £18,095. Add £500 for
the five-door version. The Golf GT 168bhp with a fast-shifting DSG automated transmission costs £19,925.

As a price comparison, the outgoing Golf three-door with the 2.0-litre FSI engine was priced at £17,275, showing the new TSI engine has a price premium of £820. Volkswagen says that because there are other changes to the specification of the vehicle a direct price comparison
is not accurately possible.

The Golf Plus Sport 139bhp is priced at £17,215 and 139bhp Touran models start at £17,995.

Volkswagen UK says this year their sales prediction for all Golf models
is 60,000 units with the new TSI 139bhp and 168bhp models each taking around 2 per cent of sales — approximately 2,400 units in total.
For Touran, the UK sales this year will be around 11,000 units and
the TSI 139bhp models will also account for 2 per cent of sales — 220 units.

When you look at the 'paper' specification and performance figures
for VW's new 1.4-litre TSI dual-charged petrol engine and see it is
more powerful, faster, more fuel efficient and less polluting than the relatively-new 2.0-litre FSI direct injection petrol engine, it's hard
to believe what you're reading can be possible.

But, I can assure you, it most certainly is. At last, a petrol engine which drives like a diesel but is quieter although not yet quite as frugal with fuel. Turn the ignition key and the new 1.4-litre unit springs into life — no diesel rattle or clatter. Slip it into first gear and accelerate. Change up to second, third, fourth and so on and there is a huge amount of power. And, more importantly, torque — making the car easy to drive at slow speeds in town or in traffic. On the open road, thanks to supercharger and turbocharger power or a mixing of both, the engine is really responsive and strong during acceleration. There are no steps between these boosted stages. It is a petrol unit, but
it's just like driving a diesel. Remarkable.

The UK is learning to like diesel power, and the quality of driving and fuel economy and low taxation levels these engines give. What they don't like is the engine noise. TSI technology really will appeal to the diehards who want to remain petrol car users and I can see TSI con-verting a few diesel users back to petrol. Perhaps the fuel economy is not yet quite as good as a diesel engine, but it is not too far away. And the VW TSI's service intervals, costs and warranty cover are no different to a conventional FSI petrol engine.

During my brief drive this week in the 139bhp TSI-powered Golf Sport 3-door, the test car returned 36.2mpg — very close to VW's quoted 39.2mpg for the combined cycle. In the Touran, the 139bhp unit
should return 37.7mpg. Again, my test car came very close, returning 35.6mpg. That's good, but what is even better is that the Golf 5-door fitted with the 168bhp unit returned a 42.9mpg — nearly 5mpg better than the official fuel consumption of 38.2mpg! All these drives took place over the same route and the same traffic conditions, so they're pretty accurate comparisons.

There is no doubt about it — the fuel economy potential is there. But what is most impressive is that such a relatively small engine can give the quality of driving and acceleration only found in much larger petrol engines or with diesel units. TSI technology is a very big step forward. In addition, TSI powered Golfs come with all of the plus points of petrol and diesel engines in one. A slight price premium over FSI models is a very small price to pay. So, Volkswagen, Well done! — David Miles

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Volkswagen Golf GT 1.4 TSI 5-door | £18,595
Maximum speed: 137mph | 0-62mph: 7.9 seconds
Test MPG: 42.9mpg | Power: 168bhp | Torque: 177lb ft

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------------------------------------------------------------ Volkswagen Golf GT