[///M1]

Originally Posted by Pete_vB

Well I'd say we're just asking for clarification at this point. Doubting may come later. I'm certain we'll get some more tests, and some of the guys with boost gauges will mention if they see a difference in boost. I'm also pretty sure tuners know how the software changes with the M button...

My observations:

1. I have dynoed the car with M button on, and with it off (in consecutive runs). No change in observed peak HP numbers.
2. I have a boost gauge (get's physical readings through DV lines as opposed to the CANbus version). No observed difference in peak boost between M and non-M mode (15psi peak on stock tune regardless if M button is engaged).
3. I have also logged the car in multiple parameters, peak included, through the AccessPort. Again no difference in peak boost was noticed whether M button was activated or not (via ECU readings this time).
4. Tuners like COBB have maps which disable the M button all-together (e.g. their 91 and 93 Linear Throttle maps where there is no difference if you depress the M button or not). This results in no change in recorded peak power as compared to there Non-Linear Throttle maps (where the M button is allowed to work). All it changes is sensitivity on throttle response, not peak power (nor boost).
5. I dynoed my MadDad mid pipe + Akra Slip-On and got a 10whp delta gain. Compared to the N55 mids, the MadDad is no less restrictive, in fact I'd venture to guess to say it is even freer flowing. Unless one can argue the Akra Slip-On (valves fully open) exhaust is more restrictive than stock (close to an impossibility), getting the alleged gains from an N55 mid pipe alone certainly look very optimistic. FWIW, I had the MadDad midpipe on my 135i and it recorded 8whp gains.

At the end of the day, I personally don't think the M button is any different than what I had on my E39 M5 (basically a factory-installed Sprintbooster that changes throttle response). What has documented here is definitely in contradiction, so I too would like to know what occurring.