Boosting a teensy engine to huge horsepower numbers invariably results in a lot of turbo lag - a turbocharger large enough to produce big boost at high rpm won't be able to spool quickly. If you've ever driven a Subaru WRX STI, you know this phenomenon well - you have little or no boost at low rpm, but keep your foot mashed long enough, and the turbo spools up and kicks you in the pants.
Volkswagen used the supercharger to keep boost levels up when the turbo isn't spooled, so that when you're off-boost, the 1.4-liter feels more like, say, a 1.8-liter. The turbo demonstrates some lag - a bit more than the turbo-only 2.0T - but the transition between turbo lag and turbo boost is nowhere near as dramatic as it would be without the supercharger. You can feel some surging as the tach needle makes its way from idle to redline, no doubt a result of the engine computer managing the boost levels, but otherwise, you'd have no idea that the 1.4 TSI was twin-charged.
Power and fuel economy
160 hp isn't a huge amount of power in a modern car, but the Scirocco is quick in a straight line. Volkswagen claims the 6-speed manual Scirocco 1.4 TSI will hit 62 mph in 8.0 seconds, and its top speed - which I verified over miles and miles and miles of Autobahn - is 135 mph. At an indicated 138 mph in sixth gear, the trip computer shows that the little engine is sucking down super unleaded at the alarming rate of 10.6 mpg. (The Scirocco will maintain an indicated 137 mph in fifth, slurping a gallon every 9.9 miles!)
At U.S.-highway speeds, however, the fuel economy is pretty impressive. At a constant 62 mph, the computer showed 47 mpg; at 75 mph it dropped only to 33 mpg. Those numbers are consistent with its European-cycle fuel economy ratings of 27 mpg city, 44 highway. The 2.0T, by comparison, is rated at 22 city, 40 highway - and its 200 hp propels the Scirocco to 62 mph in 7.2 seconds and on to a top speed of 146 mph.