What does the M button really do in technical detail?

[Plaz]

Originally Posted by GoingTooFast

The M button only gets you a sharper throttle response mapping. Unlike the new M5 the 1M engine (N54) doesn't have the VALVETRONIC feature (the single-turbo N55 engine in the late 135i does have it though).

Then why does Herr Poggel say it does?

[Fundahl]

You can modify wastegate duty cycle without Valvetronic. Having the wategates normally closed (M button on) decreases spool time and gives a harder/faster kick when transitioning from partial to full throttle.

Without the M button on, the wastegates are normally open to reduce backpressure/pumping losses and increase efficiency.

[GoingTooFast]

Originally Posted by Plaz

Then why does Herr Poggel say it does?

Isn't he talking about the new M5?!

You can only get access to the OVERBOOST function (wategate late opening) with the M button ON.

[bdaddylo]

Originally Posted by GoingTooFast

Isn't he talking about the new M5?!

You can only get access to the OVERBOOST function (wategate late opening) with the M button ON.

Overboost has nothing to do with the M button.

[diegorst]

Originally Posted by bdaddylo

Overboost has nothing to do with the M button.

+1

[MusclezMarinara]

Originally Posted by diegorst

+1

Just floor the bitch thats your overboost

[Mdawood]

I'm confused... I thought the m button was for super pursuit mode?

[v1k0d3n]

i thought there'd be more mechanics or something on this board? this goes back to a post i created when i first joined...looking for a 1M shop/repair manual. this would explain everything! is there an M specific shop/repair manual available yet? everything that BMW does is computer/internet based, but I would sure love to have a DVD version or something for myself if I could.

[GoingTooFast]

Originally Posted by bdaddylo

Overboost has nothing to do with the M button.

The WG is used to regulate the charging pressure. A boost controller decides how much air to escape out the WG to keep the turbo speed at what it needs to feed the engine at its boost target. If the WG remains closed the exhaust gas always passes over the turbine which then runs at a considerably higher speed. With the M button ON and at WOT, the WG stays closed until it hits its overboost target, it holds it at that level for a couple of seconds then opens more to run the boost down to held level.

Since the M button changes the WG settings, it also changes the overboost function (500Nm of torque).


M button function:

1. Sharper throttle response mapping;
2. Overboost;

[josephvman]

Originally Posted by Mdawood

I'm confused... I thought the m button was for super pursuit mode?

For Super Pursuit you have to push the M, and also turn off the AC.

[Fundahl]

Like and i others have said, the M button seems to change wategate operation and pedal position vs load requested.

That qualifies as mechanical change M button on vs off.

[bdaddylo]

Originally Posted by GoingTooFast

The WG is used to regulate the charging pressure. A boost controller decides how much air to escape out the WG to keep the turbo speed at what it needs to feed the engine at its boost target. If the WG remains closed the exhaust gas always passes over the turbine which then runs at a considerably higher speed. With the M button ON and at WOT, the WG stays closed until it hits its overboost target, it holds it at that level for a couple of seconds then opens more to run the boost down to held level.

Since the M button changes the WG settings, it also changes the overboost function (500Nm of torque).


M button function:

1. Sharper throttle response mapping;
2. Overboost;

Overboost occurs regardless of whether or not the M button is activated. The only difference may be is that overboost is achieved quicker in M mode because the wastegate is already closed. It doesn't mean there's more boost.
Not sure why you still think overboost is linked to the M button. It's not that complicated.

[clived]

Originally Posted by GoingTooFast

Since the M button changes the WG settings, it also changes the overboost function

Sorry, like others here, I have to call BS on this one. Surely just by trying this out on your own 1M you'd know this not to be true?

[rapter]

Originally Posted by GoingTooFast

The WG is used to regulate the charging pressure. A boost controller decides how much air to escape out the WG to keep the turbo speed at what it needs to feed the engine at its boost target. If the WG remains closed the exhaust gas always passes over the turbine which then runs at a considerably higher speed. With the M button ON and at WOT, the WG stays closed until it hits its overboost target, it holds it at that level for a couple of seconds then opens more to run the boost down to held level.

Since the M button changes the WG settings, it also changes the overboost function (500Nm of torque).


M button function:

1. Sharper throttle response mapping;
2. Overboost;

Can we put a nail in the coffin and get an official technical understanding on how the overboost works in this car?

[evoiii90]

From BMW's 1M technical training documentation (Technical Training, E82 M Complete Vehicle, BMW Group University, ST1104)

The effect of the M Engine dynamics control Sports mode on the BMW E82 M Coupe is to further increase the responsiveness of the acceleration compared with the already very direct response of the basic setting (conversion of pedal sensor position to power delivery)

This is what most have been saying all along, the M button changes the sensitivity/mapping of the throttle pedal, much like like the Sport mode in E9x M3s and even the old E46 M3.

This function is comparable with the M Engine dynamics control Sports mode on the BMW E9x M3. On that model, it is activated by the Power button on the center console.

The next paragraph says:

In addition, control of the turbochargerwastegate valves is programmed for maximum turbocharger speed in the lower power band for enhanced responsiveness. This produces a further gain in dynamic response when accelerating from a constant speed and adopting a positive driving style.

This is basically what "Fundahl" was saying before:

Originally Posted by Fundahl

You can modify wastegate duty cycle without Valvetronic. Having the wategates normally closed (M button on) decreases spool time and gives a harder/faster kick when transitioning from partial to full throttle.

Without the M button on, the wastegates are normally open to reduce backpressure/pumping losses and increase efficiency.

Now this means the overboost function will KICK IN SOONER, it DOES NOT mean the engine is going to deliver more power because there was an extra increase of boost pressure, ONLY SOONER. There is NO EXTRA power compared to the regular overboost function.

Originally Posted by GoingTooFast

The WG is used to regulate the charging pressure. A boost controller decides how much air to escape out the WG to keep the turbo speed at what it needs to feed the engine at its boost target. If the WG remains closed the exhaust gas always passes over the turbine which then runs at a considerably higher speed. With the M button ON and at WOT, the WG stays closed until it hits its overboost target, it holds it at that level for a couple of seconds then opens more to run the boost down to held level.

Since the M button changes the WG settings, it also changes the overboost function (500Nm of torque).


M button function:

1. Sharper throttle response mapping;
2. Overboost;

I will say this is partially correct, I will only add that the M button changes WHEN the overboost kicks in, not by HOW MUCH.

Originally Posted by bdaddylo

Overboost occurs regardless of whether or not the M button is activated. The only difference may be is that overboost is achieved quicker in M mode because the wastegate is already closed. It doesn't mean there's more boost.
Not sure why you still think overboost is linked to the M button. It's not that complicated.

This is again partially correct. As I said before and as BMW's documentation says, it only changes WHEN, not by how much so we CAN say it DOES change the overboost function by determining WHEN it engages.

Lastly, here is another paragraph of the same document:

As on the BMW Z4 sDriveSSis, the maximum torque of 450Nm/295 ft Ibs is briefly raised (for five sec¬onds max.) to 500Nm/369 ft Ibs by the overboost function. The precondition for the overboost function is a demand for acceleration of more than 80%. The increased torque is available from as low as 1,500 rpm right through to 4,500 rpm. That means that the torque gain can be as much as 100 Nm compared to the BMW 135i.

Based on all this I guess we can put this one to rest.... Attached is the page where I extracted all this...

[ayao]

Brilliant. Maybe it should even be stickied...

[bdaddylo]

Originally Posted by evoiii90

This is again partially correct. As I said before and as BMW's documentation says, it only changes WHEN, not by how much so we CAN say it DOES change the overboost function by determining WHEN it engages.

I disagree with you. The document does not specify any changes to the overboost function. The programming of the wastegate valve in M mode only changes the responsiveness of the turbo and all this does is allow the turbo to spool up quicker. Overboost still occurs when the demand for acceleration is greater than 80%.

[sparoz]

Originally Posted by bdaddylo

I disagree with you. The document does not specify any changes to the overboost function. The programming of the wastegate valve in M mode only changes the responsiveness of the turbo and all this does is allow the turbo to spool up quicker. Overboost still occurs when the demand for acceleration is greater than 80%.

edited: I feel more civilised after work.

The document does not specify any changes to the overboost function, but the parameters for the overboost has changed when the M button is pressed. The 80% demand for acceleration itself is just a precondition, but not a causation of overboost according to the article. Whether the overboost occurs still depends on other conditions, and optimal traction is an overriding condition. The articles further explained that the reasons why overboost rarely occurs or minimal in 1st or 2nd gear, while you get more overboost in 4th gear than 3rd gear.

The article clearly stated that the M button does two things: a) changes the engine mapping, b) closing the wastegate. It also further explains this is the reason why the DSC will tend to kick in more often when the M button's pushed. With these changed parameters, the behaviour of the overboost will change.

In reality, that also explains why I don't feel the overboost when M button is not on, whereas I can feel the kick when the M button is pressed. It is probably more relating to the engine mapping and the faster response that causes the overboost to come in quicker (time wise).

[sparoz]

Originally Posted by ayao

Brilliant. Maybe it should even be stickied...

+1

[GoingTooFast]

Originally Posted by bdaddylo

The programming of the wastegate valve in M mode only changes the responsiveness of the turbo and all this does is allow the turbo to spool up quicker. Overboost still occurs when the demand for acceleration is greater than 80%.

If that is so, then you should note NO difference between M Engine dynamics control Sports mode ON and Sports mode OFF when drag racing against the clock because in that situation the demand for acceleration is ALWAYS greater than 80% with 'Power Shifting' - your foot is kept on the gas during each speed-shift. (You will need to make your shift quickly enough so that you do not hit the rev-limiter!)

Try it with your 1M... if you are right, then you CAN'T be quicker on the clock with the M button ON because you would have the exact same max. torque between 1500-4500rpm (responsiveness of the acceleration - the dynamic response when accelerating from a constant speed - doesn't play a role here) !!!

[GoingTooFast]

I bet you are quicker with the M button ON...

[sparoz]

Originally Posted by GoingTooFast

I bet you are quicker with the M button ON...

Dan reckons he's quicker with the M button off .