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2Addicts | BMW 2-Series forum Technical Topics N55 (M235i) Engine, Transmission, Exhaust, Tuning BMW M2 Anti-Lag braaap sound after lifting the throttle

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      09-23-2019, 05:11 PM   #1
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Exclamation BMW M2 Anti-Lag braaap sound after lifting the throttle

Hello everyone,
I have been thinking about what makes this "braaap" sound after lifting the throttle in M2 (non competition). It is done by the wastegate right?

Could I possibly implement it on M235i/M240i by purchasing DME/turbo&exhaust manifold from M2 and putting it on 235i/240i?

The sound I'm looking for:


It sounds like anti lag system, Just to be clear, I'm not looking for other burble tune.


Thanks!
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      09-23-2019, 09:29 PM   #2
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I'm also curious to learn what causes this sound!
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      09-25-2019, 02:42 PM   #3
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Same, following
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      09-25-2019, 05:02 PM   #4
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It sounds like fuel over-run. Basically unburnt fuel in the exhaust, exploding.
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      09-26-2019, 05:47 AM   #5
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Quote:
Originally Posted by Jeff@TopGearSolutions View Post
It sounds like fuel over-run. Basically unburnt fuel in the exhaust, exploding.
Well, it's not a simple burble tune. As I said, it more like ALS.

Here's a quote from @Andrew

Quote:
So basically the answer is yes it is possible, but technically, as of now I don't believe there is any off the shelf options to achieve this, It would need to be hard flashed not something simply coded, a retrofit of m2 n55 engine parameters would possibly be the answer, the hardware is all there between the two cars, flash tune manufactures are focused on fuel dumping for flame maps or "ak47" burble and not so much the OEM M throttle lift, I enjoy the sound as well and was interested in retrofitting

Basically BMW is using the DME to controlling fuel sending more when the throttle goes to close in order to keep the turbo/turbos spooling in order to mitigate lag thats what is going on from my understanding, the m2 has pretty much the same engine as the m235, there are differences but not enough to make an engine parameter from one incompatible with another as far as I know

I ended up selling my m235i and now have an f80 so I never continued to search for the answer to this, I would think it is possible to contact someone who creates DME flashes, such as bootmod3, in the parameter entries there must be a specific location that controls overrun, distinguishing the difference between the non m n55 and the m n55 and would be a simple addition as it already exist
So I'm wondering now if my local tuner could adopt M2 DME into m235i.
Used DME for M2 cost around ~1.2k I believe.




Quote:
Originally Posted by Darubba View Post
Nice video
With catless downpipe it sounds even better!
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      09-26-2019, 08:32 AM   #6
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i believe the difference on the limiter in sound between a m2 and normal n55 (235 etc) is that the m2 has a hard cut limiter that makes that aggressive braap noise. if you look at the m2 rev gauge when its on the limiter it bounces a lot more aggressively then a 235.
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      09-26-2019, 10:38 AM   #7
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My 228i does a similar sound on upshifts after muffler delete. Not as pronounced though. The M2 has a more aggressive exhaust then the normal 2 series, so it makes sense.
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      09-26-2019, 05:34 PM   #8
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Exclamation

Quote:
Originally Posted by ChristosD View Post
i believe the difference on the limiter in sound between a m2 and normal n55 (235 etc) is that the m2 has a hard cut limiter that makes that aggressive braap noise. if you look at the m2 rev gauge when its on the limiter it bounces a lot more aggressively then a 235.
I don't think that's the case here.

Quote:
Originally Posted by ngl View Post
My 228i does a similar sound on upshifts after muffler delete. Not as pronounced though. The M2 has a more aggressive exhaust then the normal 2 series, so it makes sense.
What you are saying is a standard sound when you are upshifting.

Tech Part:
Quote:
Originally Posted by Boss330 View Post
With valvetronic, you can have better control of valves (I guess?). For instance creating a "blow through" situation where the injected fuel is ignited but the combustion pressure isn't trapped inside the combustion chamber but released through the exhaust valves (intake valves must be closed during this stage to avoid the pressure escaping to the intake manifold) and thereby spinning the turbos. Sort of like igniting fuel in a container with a small opening, creating a "jet stream" of hot air (exhaust). That "jet stream" will keep the turbos spinning at a high rpm (stated to be around 100.000rpm!!!). Since the combustion pressure is bled out through the exhaust valves, engine braking shouldn't be adversely affected perhaps?

And I also believe that this "jet stream" will be able to sustain a certain boost pressure even under deceleration. At least that would be beneficial in reducing lag, as otherwise the turbos will need time to raise pressure. With a "anti lag base pressure" of say 0.5bar, the engine would feel much more responsive and lag will be virtually non-existent.

For the cylinders that "participate" in the anti lag function this is how I imagine the system works:

Stage 1: Air enters combustion chamber (intake valves open, exhaust valves closed - intake stroke)
Stage 2: Air is compressed (intake and exhaust valves closed, creating engine braking - compression stroke)
Stage 3: Fuel is injected and spark is introduced (both intake and exhaust valves closed, or possibly starting to open exhaust valves here - combustion stroke)
Stage 4: Combustion starts and exhaust valves are opened to vent exhaust (intake valves closed, exhaust valves open - "exhaust stroke")

Stage 1-3 is equal to a normal 4-stroke combustion cycle
Stage 4 is different because the combustion energy isn't used to push down the piston, but to create a "jet stream" of exhaust gases to the turbos and spinning them.

Fuel injected in this "anti-lag" process is measured to create a combustion needed to spin the turbos, not the same amount of fuel needed to push down the piston in a normal 4-stroke cycle.


I'm pretty sure that emission and mileage data is at the normal settings for all cars on sale today.

Quote:
Originally Posted by CanAutM3 View Post
Good analysis .

I agree that, with this feature, it is possible to keep the car "on boost" with "closed throttles". To achieve this, the intake valves would need to open as little as possible on a few cylinders (while remaining closed on others) to just sustain the exhaust "jet stream" you mention. With the intake valves mostly closed there is very little air flow into the engine and the turbos do not need to produce much work to maintain boost. By precisely adjusting the bleed off valve and Valvtronic, the turbo speed and boost pressure can be maintained.

It is very similar to an old driving technique I learned in rally school. Left foot brake to slow the car down but keep the right foot on the throttle to keep the turbo spinning and on boost (I know, there are other reasons to left foot brake but this is also one of them )
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      09-30-2019, 12:22 AM   #9
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Quote:
Originally Posted by Thomas590 View Post
I don't think that's the case here.


What you are saying is a standard sound when you are upshifting.

Tech Part:
have a read through this thread here(page 118-119) i been trying to find out why it makes a different noise for a while now, its killing me lol

https://www.e90post.com/forums/showt...18714&page=118
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      10-01-2019, 04:29 PM   #10
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Are you talking about the fart in between shifts? That's the wastegate releasing boost between shifts...
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      10-02-2019, 07:13 PM   #11
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Lightbulb

Quote:
Originally Posted by ChristosD View Post
have a read through this thread here(page 118-119) i been trying to find out why it makes a different noise for a while now, its killing me lol

https://www.e90post.com/forums/showt...18714&page=118
Check out this thread, it might help you to find the answer.
https://f80.bimmerpost.com/forums/sh....php?t=1211456


Quote:
Originally Posted by nioh_lbbm2 View Post
Are you talking about the fart in between shifts? That's the wastegate releasing boost between shifts...
How can you be sure of this that it's a wastegate?

Quote:
Originally Posted by CanAutM3 View Post
When abruptly lifting the throttle on the S55, "farting" noises can be heard. There is some wizardry happening in the engine system to keep the turbos spooled. It is most probably a combination of the waste-gates, Vanos and fuel injection that come into play to maintain high energy gases in the exhaust.

Quote:
Originally Posted by Boss330 View Post
As far as I know, very few production turbo engines employ anti lag by using an open throttle and injecting fuel. The S55 and Porsche 991 Turbo S has at least "cold blowing". That is, keeping the throttle/valvetronic open on the overrun so that the engine continues to pump air and spool the turbo. The 991 Turbo S only introduced this technology on the facelifted version going on the market this year.
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      10-03-2019, 12:18 AM   #12
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Quote:
Originally Posted by Thomas590 View Post
Check out this thread, it might help you to find the answer.
https://f80.bimmerpost.com/forums/sh....php?t=1211456



How can you be sure of this that it's a wastegate?
But the vid is of an m2 with an n55 not s55, it might employ similar tech maybe? But doubtful.
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      10-03-2019, 04:49 AM   #13
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Quote:
Originally Posted by Luftwaffe1O1 View Post
But the vid is of an m2 with an n55 not s55, it might employ similar tech maybe? But doubtful.
Check out the differences between M235i and M2 (Non comp pkg).
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      10-03-2019, 01:41 PM   #14
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Doesn't the M2 use the N20 Wastegate?
I'll ask my tuner what the difference is.
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      10-05-2019, 12:42 AM   #15
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im talking about the sound the m2 makes on the limiter when you rev it it cant be a gearbox related noise as the manual makes the same sound.
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      10-05-2019, 01:24 AM   #16
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I looked into this a bunch and reached out to both Wedge and PureBoost about it.

Wedge said that they had looked into it before and hadn't been able to figure it out. Ken suggested getting in touch with Fabian and PureBoost. I contacted Fabian who also said he had been trying to find the parameters that make the M2 do this overrun but hadn't yet found it - and said he would get back in touch with me.

It is definitely overrun controlled by the DME though. Though the throttle closure on the M2 might also have something to do with it.

I've wanted this sound badly on my M235 for a while lol.
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      10-05-2019, 10:39 AM   #17
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Quote:
Originally Posted by sea_m235i View Post

I've wanted this sound badly on my M235 for a while lol.
Like all of us
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      10-07-2019, 02:03 PM   #18
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Quote:
Originally Posted by sea_m235i View Post
I looked into this a bunch and reached out to both Wedge and PureBoost about it.

Wedge said that they had looked into it before and hadn't been able to figure it out. Ken suggested getting in touch with Fabian and PureBoost. I contacted Fabian who also said he had been trying to find the parameters that make the M2 do this overrun but hadn't yet found it - and said he would get back in touch with me.

It is definitely overrun controlled by the DME though. Though the throttle closure on the M2 might also have something to do with it.

I've wanted this sound badly on my M235 for a while lol.
i genuinely think this is true sounds like a hard cut limiter i think they did this to make the m2 sound more aggressive as i cant see the performance benefit
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      10-09-2019, 06:49 PM   #19
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Quote:
Originally Posted by ChristosD View Post
i genuinely think this is true sounds like a hard cut limiter i think they did this to make the m2 sound more aggressive as i cant see the performance benefit
That's completely something different. Hard cut limiter on 4500 RPM?
It's more like soft limiter but ALS (Anti-Lag System) kicks in and that's why you hear it.

Pretty much all M cars does this right now (maybe besides newest M5).
Definitely not a "hard cut limiter", even the thing with wastegate which @nioh_lbbm2 said is more realistic than hard cut limiter.




Make sure to analyze those two videos.
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      10-11-2019, 03:31 PM   #20
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Not sure if it's because of this thread, but a customer came to me with this thing.

I'll try over the weekend to flash my N55 EWG with the M2 files for testing.
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Last edited by julienjj; 10-11-2019 at 04:31 PM..
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      10-13-2019, 09:54 AM   #21
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Quote:
Originally Posted by julienjj View Post
Not sure if it's because of this thread, but a customer came to me with this thing.

I'll try over the weekend to flash my N55 EWG with the M2 files for testing.
I don’t think that will work. Doesn’t BM3 have a stock M2 map - does that give you the sound? Very interested in this.
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      10-14-2019, 09:10 PM   #22
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The BM3 m2 maps just transfer over the basic M2 parameters. The M2 use totally different software BUT the same hardware. Normally BMW protect those by FSC (Preventing you from flashing the 320i into a 328i) but the M2 DME is running an incompatible eeprom so it seems they didn't bother

Replacing the eeprom in the DME is not something that can be done by bootmod or by OBD at all.
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