Many engines and intake systems rely upon "resonant effects" for optimal performance and high volumetric efficiencies. As I understand, all of BMW's ///M cars with the S54 engine incorporate such resonant effects, particularly with the runner lengths inside the plenum, immediately in front of the throttle bodies.daz05 wrote: More noise must mean less pressure?
There appears to be a strange phenomenon specific to the Z4M, related to the recorded powerband, which shows a drop in power at around 7200rpm followed by a rebound around 7600rpm, as shown in a typical dyno plot, as below. This doesn't seem to occur in the E46 M3, and so I wonder whether this phenomenon is caused by resonant effects which are related to the Z4M's unique air intake system upstream of the plenum? Since pilchardthecat's CF air-filter box mod will have different resonant characteristics to OEM, it would be interesting to know, what changes to performance, if any, this mod has?
From datalogging in "real world" driving conditions, this drop in power at around 7200rpm is clearly shown by a reduction in air-flow rate through the MAF coupled with a slight deceleration of engine rpm, followed by a surge in airflow and an increase in engine rpm acceleration, as if the engine has taken a sudden gulp in air for a "second wind".