The Z4 is not at all impressive. The 3 litre puts out 220 HP. The 2.5 litre puts out 183 HP. Unless the car is a Z4 Alpina V8 it aint got nothing for the Z28. The Z4 Alpina will be about even with an LT1 car a little less than a match for an LS1. Racing the other vairants would be like clubbing baby seals for most Z28's or Cobras.