In reply to z31maniac :
There are... advantages. Lower compression with higher boost gets more mass into the engine, and ultimately it is mass flow in and out where most of your power comes from. Low compression and high boost also gives a longer, smoother pressure curve, which is easier on the bottom end.
I'd also like to say that it's better as far as heat loads go, but I'm not 100% on that.
Audi DID raise the compression to 6.6:1 for the 4v engines. It was 6:1 for the 2v engines. With a giant turbo with a huge hotside for maximum power with minimal heat stress. It's no wonder that they invented air-recirculating antilag, and the twin-clutch trans so they didn't have to lift to shift. (YES! They ran PDK transmissions in some cars in 1986) They had a laser-like focus on making power, with little thought to drivability or chassis handling.
Meanwhile, when they used a restrictor to limit mass flow into the engine, 15 years later Lehmann (builders of Skoda engines, which were VW/Audi fours of the same architecture as the Group B Audi fives) was running compression in the 11-12:1 range (allegedly: info is not easy to get) to get every bit of power of the air they were allowed to get into the engine, and aluminum rods to cushion the pressure spikes.
