At what RPM does the extra turbo boost/torque kick in?

[Luca335]

After my break in, I was testing the car. I felt the extra boost/torque push came at about 4500 rpm, both in regular and M sport mode.

What about you?

[1'M Blue]

Its usually somewhere arond that range yes

[mPlasticDesign]

My understanding is overboost is triggered by WOT, not 4k RPM or any specific RPM. And lasts for ~7sec.

[MDORPHN]

Originally Posted by Mr.Metak2you

My understanding is overboost is triggered by WOT, not 4k RPM or any specific RPM. And lasts for ~7sec.

BMW has been very careful about not providing specific info about overboost.

AFAIK, it's triggered under "high load, low rpm" conditions and lasts between 4 and 7 seconds.

Neil

[Pete_vB]

Originally Posted by Luca335

After my break in, I was testing the car. I felt the extra boost/torque push came at about 4500 rpm, both in regular and M sport mode.

What about you?

It's mainly lower in the rev range, from wherever you hit full boost (around 2k) tapering off around 5k. See this dyno comparison- the N54is is very similar to our motor, and that extra torque is primarily from the overboost:

[robertm]

I'm sure this has been covered somewhere before but does the M button need to be pressed for the overboost become active? Or is it simply full throttle which will activate under the right circumstances? I really don't like that stupid button but will use it I guess if its the only way to get the extra torque.

[mPlasticDesign]

Originally Posted by Pete_vB

It's mainly lower in the rev range, from wherever you hit full boost (around 2k) tapering off around 5k. See this dyno comparison- the N54is is very similar to our motor, and that extra torque is primarily from the overboost:

Nice post! Yeah I was pretty sure it was triggered by the WOT and makes sense that it stops around 5k RPM. I'm sure BMW wouldn't want it near the 6-7k(redline) range!

[PyratOne]

Originally Posted by robertm

I'm sure this has been covered somewhere before but does the M button need to be pressed for the overboost become active? Or is it simply full throttle which will activate under the right circumstances? I really don't like that stupid button but will use it I guess if its the only way to get the extra torque.

No, the M-button on the steering wheel is for throttle response only. Overboost you get by mashing the pedal. Once you've had the throttle reponse M-button "on" and driven for a while, you'll notice when its off. Almost like the car is neutered.

Traction control on the dash is for stability(edit: owners manual is very clear that we dont have "dynamic traction control". Its "dynamic stability control" Whatever.....its fun with it OFF whatever it is!!). Default is all nannies 'on' when car is powered up. One push=MDM m dynamic mode which is some nannies 'off'. Hold button 3 seconds = all traction control OFF.

Thse three functions together (M-button, overboost, traction OFF) make the car a completely different beast. For normal driving, I turn off all the good stuff. Its easy to get in trouble with it all on - you'll want to explore the limits.

[Amnizu]

Originally Posted by Mr.Metak2you

Nice post! Yeah I was pretty sure it was triggered by the WOT and makes sense that it stops around 5k RPM. I'm sure BMW wouldn't want it near the 6-7k(redline) range!

It's probably because of the turbo and exhaust design. Smaller turbos that offer torque in the lower range are much less efficient in the higher range RPM. Also, cats restrict exhaust exit velocity at higher RPM and the factory intercooler probably cannot provide enough cold air to allow boost to be held until redline. This is why most modern turbo engines taper boost approaching redline.

TL DR; at high RPM small turbos and intercoolers become hot air blowers and restrictive exhaust prevents the engine from fully breathing.

[135IS]

when i turn my jb4 on

[robertm]

Originally Posted by PyratOne

Thse three functions together (M-button, overboost, traction OFF) make the car a completely different beast. For normal driving, I turn off all the good stuff. Its easy to get in trouble with it all on - you'll want to explore the limits.

As long as its dry, my standard procedure when I get in the car is to push the traction control button until it’s all the way off.

I'm just not a fan of the M button at all though. I feel like it turns the gas petal into an on off switch. The car is already pretty sensitive with the quick spooling turbos but with the M button I lose almost all ability to roll on and off the throttle. I really don’t like this when I’m pushing the limits in a turn. Plus it makes no difference at full throttle as far as I can feel.

I like be able to modulate the throttle input at partial throttle and if I'm mashing the petal it doesn't seem to make any difference. So, I just don't see a benefit and definitely feel it detracts from proper involvement at partial throttle inputs.

[Simsims]

Originally Posted by robertm

As long as its dry, my standard procedure when I get in the car is to push the traction control button until it’s all the way off.

I'm just not a fan of the M button at all though. I feel like it turns the gas petal into an on off switch. The car is already pretty sensitive with the quick spooling turbos but with the M button I lose almost all ability to roll on and off the throttle. I really don’t like this when I’m pushing the limits in a turn. Plus it makes no difference at full throttle as far as I can feel.

I like be able to modulate the throttle input at partial throttle and if I'm mashing the petal it doesn't seem to make any difference. So, I just don't see a benefit and definitely feel it detracts from proper involvement at partial throttle inputs.

you just need to learn to feather the throttle.

M mode the throttle input is non-linear but fixed. normal mode the throttle adjusts depending on your driving. adaptation = bad, extremely bad if you're driving between stop/go traffic, highway and track.

to top that off, in M mode the wastegate is modulated to keep the turbo spooled. you can't do that in normal mode.

[Luca335]

Thanks for all the information. The weather is cooler now, does the engine/oil temperature affects the boost/extra torque? Last night it took about 20 mins of driving before the temp. gets to 90-100c. Can someone comment on this?

[silvs]

Originally Posted by robertm

As long as its dry, my standard procedure when I get in the car is to push the traction control button until it’s all the way off.

I'm just not a fan of the M button at all though. I feel like it turns the gas petal into an on off switch. The car is already pretty sensitive with the quick spooling turbos but with the M button I lose almost all ability to roll on and off the throttle. I really don’t like this when I’m pushing the limits in a turn. Plus it makes no difference at full throttle as far as I can feel.

I like be able to modulate the throttle input at partial throttle and if I'm mashing the petal it doesn't seem to make any difference. So, I just don't see a benefit and definitely feel it detracts from proper involvement at partial throttle inputs.

The main thing I like about the M button is the wastegate control. It may be me, but in between shifts things seem a lot tighter with it turned on.

My guess is that the turbos stay spooled better with the M button on.

[Amnizu]

Originally Posted by Luca335

Thanks for all the information. The weather is cooler now, does the engine/oil temperature affects the boost/extra torque? Last night it took about 20 mins of driving before the temp. gets to 90-100c. Can someone comment on this?

Couple things on this. Colder air = more HP. The colder the ambient temp the more dense the air, the more dense the air the greater the amount of oxygen, the great the amount of oxygen the higher the air fuel ratio can be pushed, the ECU should do some auto adjustments for this.

Secondly, this car has dual oil coolers behind the passenger and driver side lower air intakes. In colder weather these are going to be more effective at keeping the engine oil cool.

[Pete_vB]

Originally Posted by robertm

As long as its dry, my standard procedure when I get in the car is to push the traction control button until it’s all the way off.

I'm just not a fan of the M button at all though. I feel like it turns the gas petal into an on off switch.

I have not figure out what mode I prefer yet. I tend to agree the M button makes the throttle over-sensitive in general, I didn't realize that it also cut lag.

I don't like any of the stability options so far- Dynamic seems too intrusive in the dry in cornering, but about right in a straight line. Off makes first gear pointless- I seriously doubt that the car could possibly stick first with any tires short of drag radials, which seems silly. Even a viper is geared so that it sticks first (even with a supercharger). The slip angles with stability off in the lower couple gears get ridiculous very quickly- in the E46 M3 it was easier to modulate the slip angle as the motor was sharper and the torque not so ridiculously beyond what the tires can handle; with the 1M I'm not as comfortable dialing in the slip angle I want (so far, anyway). It seems a different stability option between Off and Dynamic should be possible, perhaps one that reduces boost in first and allows some slip angle.

[Luca335]

Did you find a big difference in fuel consumption when the M is on?

[Pete_vB]

Originally Posted by Amnizu

Couple things on this. Colder air = more HP. The colder the ambient temp the more dense the air, the more dense the air the greater the amount of oxygen, the great the amount of oxygen the higher the air fuel ratio can be pushed, the ECU should do some auto adjustments for this.

Actually the air fuel ratio stays the same, but more fuel can be mixed with the air to have more total fuel and O2 to burn. Timing can also be advanced without the risk of detonation due to the cooler mixture temps, both due to the cooler incoming air and the intercooler working more effectively.

[robertm]

So I drove home today repeatedly turning on and off the M button. Have to admit its pretty fun in a straight line. I still don't like it in the turns though. Just makes it to dam hard to dance on the limit. So new plan. Straight line stuff M button on. Once the twisties come into play M button back off. It's actually really easy to do without looking down at the wheel. It also improves my odds of making it in F1 now since I can do the steering wheel button adjustment thang

[Amnizu]

Originally Posted by robertm

So I drove home today repeatedly turning on and off the M button. Have to admit its pretty fun in a straight line. I still don't like it in the turns though. Just makes it to dam hard to dance on the limit. So new plan. Straight line stuff M button on. Once the twisties come into play M button back off. It's actually really easy to do without looking down at the wheel. It also improves my odds of making it in F1 now since I can do the steering wheel button adjustment thang

Just wait till you try and heel toe. You'll change your tune about leaving it on in the twisties.

[Sixspeed J]

Originally Posted by Amnizu

Just wait till you try and heel toe. You'll change your tune about leaving it on in the twisties.

+1. I Can't heal toe without having M button on.

[robertm]

Huh? Why wouldn't you be able to heal toe? Honestly never even consciously thought about it, definitely never had an issue with 1M. Heal toe rev match at down shift in this car is no different than any other car regardless of M button.