Originally Posted by M3takesNYC
I don't understand why it matters as the "m3" they use is really very little alike to our m3's. The z4 is also so different than a stock z4 that it comes with a stroked s65 engine which clearly is not even available.
+1, I'm surprise how many ppl doesn't understand this either. People, switching to the Z4 doesn't matter one bit. Yes, there's some minor chassisn and aero development, but all other parts on the car will be retained from the old M3.
In GTC (or whatever the GT class will be called now) these cars are built from the ground up as race cars. Yes a M3 or Z4 is no match against a Corvette and Ferrari in real life, but b/c this is regulated class racing, the Z4 will be evenly matched against cars in its class. They all have the same power to weight ratio, achieved by intake restrictors and weight restrictions. All brakes and tires are the same specs. In fact, this is one main reason why the Corvette ran the 5.5L engine instead of the 7.0L stock engine is as it's easier to conform to the max HP rating for the GTC class. This was due to the contraction of the old GT1 and GT2 classes in ALMS. GT1 ran higher hp, lower weight, more heavily developed cars.
As I recall, the Z4 used in Europe thus far has used the exact same M3 GT2 V8 and lots of the same parts. Essentially, it's the same car. Additionally, although the motor is the S65, it's very loosely based on the S65B40 in our cars. I would wager likely less than 10% of part commonality.
BMW made the switch for 2 reasons. Marketing: The E92 is at the end of it's life cycle and thus marketing cycle. They decided the Z4 should be marketed in the gap between the E9X M3 and F-Series M4.
Modifications to GTC rules: as someone has pointed out, the rules are starting to weigh against the M3 chassis which were originally designed for the old GT2 rules. But since then, they've contracted GT1 and GT2 classes.