BMW M3/M4 s55 Engine RPM Redline Projections via Technical Sound Analysis

[flinchy]

I need to say, just because it makes 400ft-lb doesnt mean it MUST make it at redline, or that it has a low redline, or anything

It could make 400ft-lb WAY before redline..

[flinchy]

Originally Posted by Mangler

I know. After the e30 they have all been mutton.

T

Mutton is great if you slow cook it

And sometimes i prefer a burger

Apples to oranges haha

If you want an analogy that no one can disagree... It's rare-medium rare slow cooked ribeye vs well done week old rump

Or mcdonalds vs in'n'out

[Mahlzeit]

In case someone feels the need to analyze another 1M, see this video. There was a camera mounted outside at the rear bumper. Granted I shifted when thrust ran out rather than rpms.

[swamp2]

Originally Posted by darmawaa

It's easy for a turbo engine to rev 8000rpm, Mc laren already did that.
What we need is low end torque (peak torque start @1500 rpm) AND 8000rpm redline.

Totally disagree.

1. If it was easy it would be much more widespread.
2. Torque at the crank is meaningless, you can't feel it and it has nothing to do with performance. Torque at the wheels does matter and the current M3 has plenty of that. The only benefit of massive low rpm torque is if you have a desire to never shift (lazy driving as I call it).

[swamp2]

Originally Posted by Mahlzeit

In case someone feels the need to analyze another 1M, see this video. There was a camera mounted outside at the rear bumper. Granted I shifted when thrust ran out rather than rpms.

So in other words it is basically useless. The idea is to verify the technique vs. a known rpm. Sure you could say we could use speed and gear to get back to rpm but that is approximation and error piled on top of each other.

[M3_WC]

Originally Posted by swamp2

Totally disagree.

1. If it was easy it would be much more widespread.
2. Torque at the crank is meaningless, you can't feel it and it has nothing to do with performance. Torque at the wheels does and the current M3 has plenty of that. The only benefit of massive low rpm torque is if you have a desire to never shift (lazy driving as I call it).

+1

[ProbyOne]

Originally Posted by ProbyOne

I also tested a few different dyno runs for various cars before convincing myself that it would work. With the right equipment it would be a pretty good way for racing teams to keep an eye (ear?) on the competition

I didn't have any good audio software on the computer and resorted to matching frequency by using this tone synthesizer http://www.philtulga.com/tone.html. Obviously Audacity is much more accurate with clear audio... I expected to be within ~5-10 Hz based on matching a few other cars really well.

I have a new appreciation for hitting the rev limiter on the dyno. We need someone to get out there with a good mic and radar gun

Just to be clear: I meant matching the audible frequency, not necessarily peak rpms (and especially so in the case of a moving car)

[Mahlzeit]

Originally Posted by swamp2

So in other words it is basically useless. The idea is to verify the technique vs. a known rpm. Sure you could say we could use speed and gear to get back to rpm but that is approximation and error piled on top of each other.

LOL,... alright, alright.

So would a video of a 1M sitting in neutral with the tach showing steady state rpms be of use? If so, what rpm?

[DANMACINSD]

If it has the same 8 speed auto tranny, third gear no longer goes to 100. It did in my 335, but in my 535 the gears are a lot closer together.

[neo871]

Originally Posted by S3RI35

"...and the new M3 will have one of the best engines we have ever done." - Friedrich Nitschke

that's all I need to know :-D

Thanks for sharing this analysis. Science rules!

+1

[JC919]

Great work!! If they offer a manual they I will need one when I get back to the states.

[Boss330]

Originally Posted by ProbyOne

I also tested a few different dyno runs for various cars before convincing myself that it would work. With the right equipment it would be a pretty good way for racing teams to keep an eye (ear?) on the competition

F1 teams did/do a lot of sound analysis of the competition. Especially a few years back, when engine revs and development was free. By doing sound analysis of the opponents engine they could get very good approximations on the HP of the other engines on the grid (max rpm, rate of frequency change (acceleration) etc.).

Based on sound analysis there was even articles in F1 magazines on which of the different engine manufacturers reached what max rpm and how much power they had.

http://www.grandprix.com/ft/ft00345.html

http://asadl.org/jasa/resource/1/jas...s2?bypassSSO=1

http://www.f1technical.net/forum/viewtopic.php?t=2218

[Kong Sheng Han]

Kinda sounds like my S54. It's still not loud enough though.

[MCaro]

Nice analysis, swamp. Just a few questions cause I am curious...
Why did you choose a hanning window?
Did you try a spectrogram to get better time/frequency resolution?
Have you tried running the audio through an adaptive FIR filter to remove white noise?

Overall it's pretty interesting. I didn't know F1 teams did something similar...

[jamdun17]

Originally Posted by flinchy

I need to say, just because it makes 400ft-lb doesnt mean it MUST make it at redline, or that it has a low redline, or anything

It could make 400ft-lb WAY before redline..

It will more then likely make its peak torque well before its redline if it would like some type of a decent power band with a high redline.

Everyone arguing about it not having a high redline is funny. 7700 rpm is high plain and simple and 7700 on a turbo car that will actually make its peak power somewhat close to that without dropping like it feel off a cliff and still be drivable would be INSANE.

For everyone touting about how the Mclaren can do it (also would like to mention that its a MCLAREN SUPERCAR with an engine probably priced as high as an M3) check out its dyno



Yep that's peak power at around 7400-7600rpm....It could have a redline of 15000 rpm, if its not making power there why the hell would you spin it that high. that's like saying i have carbon ceramic brakes but i don't track my car... oh wait ...

[bradleyland]

Originally Posted by MCaro

Nice analysis, swamp. Just a few questions cause I am curious...
Why did you choose a hanning window?
Did you try a spectrogram to get better time/frequency resolution?
Have you tried running the audio through an adaptive FIR filter to remove white noise?

Overall it's pretty interesting. I didn't know F1 teams did something similar...

I had similar questions, so I did some exploration of my own.

Why did you choose a hanning window?

I think he probably chose Hanning window because of the dynamic range of the audio data. Although I looked at rectangular as well, and the plot looked pretty good after I applied a lowpass filter.

Did you try a spectrogram to get better time/frequency resolution?

Spectrographs of mechanical sounds are really difficult to interpret. I've attached a screenshot of a short section if you're interested in looking at it. This is the region just before the upshift.

Have you tried running the audio through an adaptive FIR filter to remove white noise?

I'm not really sure what an adaptive FIR filter is. From what I gather, it would required input coefficients that would allow me to narrow the frequency range. I just used a lowpass filter as you can see in my full write-up.

==============

My analysis shows a result that's closer to 7400 RPM. If you download my files, you can open the .aup files with Audacity (it's free). Running spectrum analysis on the audio just before the upshift always gives me values closer to 330 Hz, not 350-360 Hz. Not sure why exactly.

Full write-up: http://upload.bradlanders.com/bimmer...ound-analysis/

Copy/paste of my Markdown source (links won't work, so you'll have to click here for the full version):

# F80 M3 Sound Analysis

## Goal

Identify maximum operating RPM of the F80 M3 from a video clip.

## Gathering data

Source video: REDACTED TO AVOID EMBED; SEE FULL VERSION

Extraction process: Audio captured using AudioHijack, imported to Audacity and saved in lossless Audacity internal format. Audio captured from video starting at approximately 3:04.

Full audio section:[listen](audio/f80-m3-03m04s-clip.wav) (16-bit, 44.1 KHz, PCM)

Audacity timeline (full section):


For our purposes, we will analyze the audio just before the shift "burp" heard at 4.3s. By zooming in on the timeline, we can see the change in frequency pattern with good precision. The section we will analyze is shown below:


This is a 0.300s clip, starting at 4.000s.

Clip for analysis:[listen](audio/f80-m3-analysis-clip.wav)

All my source files are available for download at the end of this document.

## Analysis

Based on a quick look at the waveforms zoomed all the way in, the audio extracted from the video appears to be a true stereo recording. Having two tracks of the same audio will confuse frequency analysis because a stereo microphone uses two separate recording sources. These two sources record different audio reflections, based on the direction and orientation of each microphone. To mitigate this, we'll split the stereo tracks, then select one for analysis. I flipped a coin and chose the right channel.

From here, we can see that we've got a pretty decent waveform to work with. Here's the clip at full zoom:


Based on rumors, we know the target redline RPM is around 7700 RPM, which translates to 385 Hz if we accept swamp2's Doppler compensation. A pure series of cylinder firing events should produce a clear series of pressure pulses at that frequency range. Anything distant from that range is either a harmonic or mechanical, wind, or tire noise.

We can use a lowpass filter to discard extraneous noise above 500 Hz, as we know that anything above this mark won't be a cylinder firing impulse pattern We could use a highpass filter as well, but let's see what the lowpass gets us first.

Apply Audacity lowpass: rolloff 48 dB, cuttoff 500 Hz.

This yields a much cleaner waveform, which should help our spectrum analysis significantly.


What we're left with is a much purer, almost sinusoidal sounding audio tone.

Filtered clip:[listen](audio/f80-m3-filtered-clip.wav)

This is the point at which we'll perform a frequency analysis. We can see from the waveform that we do not have uniform amplitude, which should be expected given that we're dealing with real world audio. The audio appears to have a dynamic range of around 1:2 to 1:3. We'll look at Hamming and Hanning windowing, as they both represent a good balance of dynamic range and frequency resolution. They're also a good fit because we've used a lowpass filter to restrict our frequency range to 0-500 Hz; the lower boundary actually being much higher than 0 Hz, as video recording equipment bottoms out well above 0 Hz.

Note: I find the plots easier to read without the grid lines, but I've provided both with and without in the download.

### Hamming window


### Hanning window


## Results

Hamming produces a peak at 325 Hz, and Hanning at 327 Hz. It's worth noting that, although I didn't show it here, using a Rectangular windowing function also resulted in highest amplitude peak around 330 Hz. I also performed analysis on the unfiltered audio, which showed similar peaks (but with more noise, obviously).

I'll be generous (to the max RPM) and use 330 Hz as the authoritative result, because of the increased resolution of rectangular window functions.

Using the same [Doppler compensation](http://www.wolframalpha.com/input/?i...370Hz%2C+90mph) figures (90 MPH), we can derive that the source frequency was around 370 Hz. This translates to 7400 RPM.

## Comments

While I found this analysis interesting, I believe there are too many confounding factors to treat the results of this sound analysis as anything more than a very broad estimate. Even if I were to stand firm that my analysis were somehow more robust than the others done here, there's no guarantee that this is the redline (maximum) RPM of the new M3. It should be noted that the vast majority of turbocharged engines deliver maximum performance when they are shifted short of their redline RPM.

## Downloads

You can download a zip file containing all images, audio files, and Audacity source files, as well as the Markdown source file for this write-up in [this 2.6 MB zip file](download.zip).

EDIT: Removed the spectrogram attachment, because it makes the thread so wide. Just download the Audacity files and have a look for yourself.

[Never Convicted]

Yep that's peak power at around 7400-7600rpm....It could have a redline of 15000 rpm, if its not making power there why the hell would you spin it that high. that's like saying i have carbon ceramic brakes but i don't track my car... oh wait ...

But that still leaves the question...do I spend $5K on my bang & Olufsen sound system BEFORE I spend $8K on my Akrapovic exhaust, or after?

[RMB]

Originally Posted by Never Convicted

But that still leaves the question...do I spend $5K on my bang & Olufsen sound system BEFORE I spend $8K on my Akrapovic exhaust, or after?

As a side note, I can't stand the upgraded sound system in my E92 M3. It isn't even in the same ball park as the Bang & Olufsen sound system in my previous 2011 Audi S4. I really hope BMW ties up loose ends with the F82 M4, not only in a performance category (usable torque without having to rev into the stratosphere and I am not lazy) but also in a luxury aspect (LED DRL's, nicer interior, better sound system, etc.) The M4 can't come fast enough for me. Like I have said before, I really like my M3, but I feel that I will love the M4. To each their own.

[swamp2]

Originally Posted by Mahlzeit

So would a video of a 1M sitting in neutral with the tach showing steady state rpms be of use? If so, what rpm?

Not really.

The only rpm useful really is redline, its a known quantity. Of course that being said limiters are not perfect and I've heard of stock M3's getting to 8460 or so before cut off. I guess that's just another variable in the mix here.

Originally Posted by DANMACINSD

If it has the same 8 speed auto tranny, third gear no longer goes to 100. It did in my 335, but in my 535 the gears are a lot closer together.

M3 and M4 will not have automatic transmissions but rather dual clutch units.

[swamp2]

Originally Posted by bradleyland

My analysis shows a result that's closer to 7400 RPM. If you download my files, you can open the .aup files with Audacity (it's free). Running spectrum analysis on the audio just before the upshift always gives me values closer to 330 Hz, not 350-360 Hz. Not sure why exactly.

Full write-up: http://upload.bradlanders.com/bimmer...ound-analysis/

Completely agree.

Although the low pass filtering, fourier techniques and stereo vs. single channel stuff are all completely irrelevant, they just don't affect the answer. My error was recording through speakers rather than internally. Even trying to repeat my process showed considerable error. After switching to recording with Soundflower the shift burble was much more recognizeable visually in the traces. I also got much more recognizable peaks in the spectral results. I agree the observed frequency is right around 330 Hz perhaps with a worst case range of about 325-335 Hz. Thus with a Doppler correction from 90-97 mph this provides an rpm range of about 7250-7550 (with rounding to 50 rpm).

This is how science works - basic peer review. Thanks for keeping me on my toes. I will revise my OP in a way to not hide my shortcoming and I'll give you the credit due.

Thanks!

[solstice]

Originally Posted by RMB

As a side note, I can't stand the upgraded sound system in my E92 M3. It isn't even in the same ball park as the Bang & Olufsen sound system in my previous 2011 Audi S4. I really hope BMW ties up loose ends with the F82 M4, not only in a performance category (usable torque without having to rev into the stratosphere and I am not lazy) but also in a luxury aspect (LED DRL's, nicer interior, better sound system, etc.) The M4 can't come fast enough for me. Like I have said before, I really like my M3, but I feel that I will love the M4. To each their own.

To me it has really nothing to do with the abilities or shortcomings ( are there really any? ) of my E90 M3. It's more that I don't keep my car past original warranty and I like something a bit different after a couple of years.

That said I spent over 10h in the car the last 2 days, all in glorious weather and many on open backroads and I had such a pang of early separation anxiety. This car is bloody awesome, the way it connects into your soul and senses is like a runners high. The new car will need to be exceedingly good to just stay on level, which I think (hope?) it will be. Everything that counts in the current M3 is superb, suspension, steering, chassi, engine, sound, seats, steering wheel, controls, tranny and overall feel. It could be the best 4 door EVER made.

[540gone]

Originally Posted by swamp2

Completely agree.

The low pass filtering, fourier techniques and stereo vs. single channel stuff are all completely irrelevant, they just don't affect the answer. My error was recording through speakers rather than internally. Even trying to repeat my process showed considerable error. After switching to recording with Soundflower the shift burble was much more recognizeable visually in the traces. I also got much more recognizable peaks in the spectral results. I agree the observed frequency is right around 330 Hz perhaps with a worst case range of about 325-335 Hz. Thus with a Doppler correction from 90-97 mph this provides an rpm range of about 7250-7550 (with rounding to 50 rpm).

This is how science works - basic peer review. Thanks for keeping me on my toes. I will revise my OP in a way to not hide my shortcoming and I'll give you the credit due.

Thanks!

^^^ THIS is a class act and that which keeps this forum valuable to all the rest of us! I have a degree in engineering (from way back) and this sort of stuff makes my spine tingle.