Originally Posted by ksfrogman
My theory is that without the DISA actuators (i.e., 3-stage differentiated intake manifold), engine management via MSV70 would have to be mapped differently to optimize the delivery of power throughout all RPM ranges, and perhaps to comply with fuel consumption and emissions objectives. The presence of resonating, overshoot and collector pipes all work in concert to maximize power output during upper engine speed ranges. However, without the actuator valves (as in the case of the 325i) to close off the pressure flow through collateral channels at lower engine speeds, engine efficiency and performance would probably be compromised at lower rpms. Too much pressure would be passed on to the next cylinder in the firing order--i.e., it might "flood" that cylinder. In order to compensate for this problem, fuel injection control, valve attenuation control (VANOS) or combination of any of the MSV70 tasks listed in the preceding paragraph are probably changed for the US 325i (vs the 330i). This could explain why the peak output of the US 325i is lower than that of the US 330i in spite of using the same engine.
Does this make sense?
Excellent info i was always wondering how the system worked as lot of other de cars use dual stage but three stage bmw has done a great job putting in actuators as i have seen a lot of them mechanical ways of letting more in at specific rpms to get the powerband going smoothly.
I think the key as you said in the quote i grabbed is the collective "concert" of the 3 stage throughout the rpm range maintaining pressure, volume and delivering at key times... offcourse the ecu would have to be programmed to be aware of this intake method to take full advantage of this... explains the smooth range in the 330.