Originally Posted by jasper
so this has me confused... if we're saying that in the 330i the optimal condition for high RPMs is with both flaps open and all chambers/paths being utilized and in the 325i the intake manifold is missing these "flaps", which would imply they are open I'm assuming, then why wouldn't the 325i make just as much torque/hp in the high RMPs?
After reading this technical explanation I would think the 325i/328i US cars would only suffer lack of torque in the lower RPM range since the intake is optimized for high-RPM. I know RichReg has posted that both intakes are otherwise identical.
So is the difference in top-end power reduced only to ECU programming? And if so, why haven't tuners extracted this power yet?
I'd love for somebody to shed some light on this... I'm sure I'm just missing something...
And thanks for posting this info. I've always wanted to see how this thing works.
This is a very good question that perhaps only some BMW tech guru could answer.
Let me give you some background info before I tell you what I think.
The N52B30 engine uses Valvetronic II technology along with the 3 stage DISA intake manifold, electric coolant pump and new Engine Management System (MSV70). These improvements resulted in a 12% reduction in fuel consumption and a 10% increase in dynamics compared with the previous M54/M56 engine.
Both the US 330i and 325i engine variants are designated as N52B30. However, the engine codes found on the driver's side of the engine block, which by the way, are very difficult to see (look between the 2nd and 3rd intake resonating pipes), are labeled either "AF" or "AE." "AF" refers to the upper ouptut stage or "OL" (High Output). "AE" refers to the lower output stage "UL" (Low Output).
The engine management system or MSV70 is responsible for many tasks: ignition control, injection control, Valvetronic II control, double VANOS, Engine temperature control, electronic collant pump control, knock control, lambda control, activation of DISA, etc.
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?