Again, I have a M54b30 and an m54b25 sitting here and I have examined the intakes and throttle bodies - i agree that looking at the intakes there does not seem to be a difference...but the TB's are different sizes
AND like you mentioned, the intake tubes from the MAF to the TB are very different (as are the MAF's)
Which injectors are you running? If using the 323 injectors, are you starving the motor?? Running it lean? What color are the injectors on the 323?
btw - I am not questioning your efforts - I am genuinly interested as I have the spare M54b25 motor sitting here and would love to find a dead 323 or 328 or 325 in swap this motor in for my daughter who will be driving in a few months.
does anyone know how much a 323 or 328 with a dead motor would cost? Needs to have clean body and interior...I can fix the rest