Originally Posted by SE3P_to_E90
325i/330i power differences are probably due to the restrictive airbox of the 325i and a much less aggressive ecu tune. my 2 cents.
The airbox of the 325i is exactly the same (Part Number 13717542018) as the one on the 330i. Both use the same air filter element, the same hot-film air mass meter, same connectors, O-ring, etc.
The tuning of course would have to be different, but do you understand why? The mechanical differences in how DISA manages intake air into the cylinders at varying rpms work in concert with Valvetronic, which by the way uses the same eccentric shaft for both the 325i and the 330i. In fact, the inlet and outlet camshafts for the 325i and 330i are identical.