Originally Posted by e36jakeo
According to this document the M3 uses 12.4 L/100km vs the Carrera which is rated at 11L/100 km, which is about 11% less than the M3. The Carrera's US mileage is rated at 18/26, so if you decrease this by 11% the M3's US figures should be 16/23.
Not great but not horrible for 420 HP.
Incorrect. You cannot accurately estimate that way. Two totally different engines.