http://www.tdiclub.com/TDIFAQ/
Shifting Gears - Much has been made about what the best shift point is for maximum economy. It is known that the engine "likes" running at around 2000 rpm, and the turbo starts kicking in at about 1500 and is going full tilt by 2000. The author prefers shifting at about 2500 rpm during normal acceleration, then when cruising speed is reached, selecting a gear which puts the revs between 1500 and 2000.
For absolute maximum acceleration with a stock engine, shift at about 4000 rpm, because power drops off quickly beyond this. There is little to be gained by shifting at 4000 compared to shifting at 3500.
For those not accustomed to manual transmissions, the TDI engine is among the easiest to learn with. The engine quickly and automatically builds up torque if the idle speed starts dropping, and the engine doesn't race away like mad upon the slightest touch of the accelerator pedal like many gas engines do. It's possible to smoothly let out the clutch and start off from a stop, then shift to second, and then to third, without touching the accelerator, and the car will pull it!
For those who don't want to shift for themselves, there is limited availability of an automatic transmission with the TDI engine.
Performance - It has been said that "people buy horsepower, but drive torque". This statement completely describes why the TDI engine is so easy to live with during day-to-day driving, despite the seemingly low horsepower rating!
A typical multivalve 2-litre gasoline engine may have its maximum horsepower (perhaps 120 or so) at 5500 to 6000 rpm, and its maximum torque (perhaps 120 lb-ft or so) between 3500 and 4000 rpm, and is probably geared to run about 2700 rpm at 100 km/h. In top gear at highway speed, the engine is below its peak torque, and probably makes around 51 hp at that speed.
A downshift is usually needed to make a quick pass, or to get up a steep hill. If the car has an automatic transmission, the torque converter will probably unlock going up moderate hills, in order to get the engine closer to its peak torque.
With the TDI engine, maximum horsepower (90) is available at 3750 to 4000 rpm, and maximum torque (155 lb-ft) is available at just 1900 rpm. The engine runs 2100 rpm at 100 km/h and makes about 62 horsepower at that speed. Hey, that's more than the gas engine ... by quite a bit, too!
Thus, no downshift is required to make a pass or to climb virtually any highway grade. And if the car has an automatic, it won't unlock the torque converter, because peak torque is right there already.
If you enter a drag race between these two cars, the gas car will probably win, because drag racing is about horsepower-to-weight ratio and little else. But who drives like that every day? Most people don't. Even people who think they do - usually don't.
For what it's worth, owners report 0 to 60 mph times with a stock car ranging from about 10.5 to 12 seconds (mostly depending on the weight of the car) and top speeds well in excess of what one ought to be doing on North American highways. In other words, not too different from the performance of a 2-litre gas engine in a similar car. The cars that the VW TDI is installed in were all designed to handle autobahn cruising at 160 km/h (100 mph) with ease and all models will exceed that easily, so if you're buying a diesel in the hope of reducing the number of speeding tickets you get, you'd better find a different excuse!