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

[e1000]

Originally Posted by ChrisK

Dang-it you beat me toooo it!

Nice car!

[1sckride]

Originally Posted by swamp2

I'm a recovering physicist and recovering engineer. Now I sell engineering software.

I dunno...sounds like you had a career in the NSA

[hellrotm]

Originally Posted by positiveions

I want to say ,realistically, it's more like 7500 rpm.

Yup, 7700 tops. 8,000 or above I would be pleasantly surprise, to say the least.

[PabloK]

Originally Posted by neo871

This is impressive! What do you actually do for a living?

Currently unemployed, but I did stay at Holiday Inn last night.


Edit: haha I just saw somebody else said this..

[Ashley Schaeffer BMW]

Impressive OP!

Some of you fail hard at reading comprehension however. No 8k redline ppl.

[Red Bread]

I've always wondered how much integrity there is in redline display? Since BMW fudges (for legal reasons) the speedo, are the tachs honest? I know dynos report the honest number, but are they always directly correlated to the indicated tachometer? Could BMW just say the F8x redlines at 7700 rpm, paint the redline there and have the engine only turn over 7400 rpm at that point, or would the moon just instantly collide with the earth, kill all mankind and doom us all?

[swamp2]

Originally Posted by kyleb350

I'm no expert in this field, but aren't there still a number of unknowns you'd need to know before making these calculations? I see you make an estimate on speed, but wouldn't gearing and exhaust acoustics also come into play? Also, it's probably a safe assumption, but still an assumption that the car is shifting at redline.

Excellent analysis though.

Thanks, gearing and exhaust acoustics absolutely affect the overall spectrum of sound (how much power/peaks occur at which frequencies). There is also a boat load of broadband wind and tire noise in the spectrum. However, you should generally have a prominent peak based on the sound directly from each piston firing and for that gearing and exhaust are not really relevant.

[swamp2]

Originally Posted by solstice

Nice!

Here's a pretty clean audio of the only production I6 turbo M car, it's in cabin but it would be interresting to see what top rpm the SW spits out.

4:24 and 4:28 for example seems like possible redline shifts.
( if you watch the whole thing you will also see two M3s showing who the daddy is )

Thanks. Although it is quick to do I don't want to analyze video after video. Anyone can do this with a plethora of free audio tools on any OS. A quick analysis of this one though around 4:24 indicated a much lower peak rpm than the 7000 rpm redline. The method is absolutely not 100% robust for all recordings but the baseline cases of the dyno runs completely convinced me that it can work. I suspect one reason here is simply the fact of internal vs. external audio. It's no doubt the design of passenger vehicles is to drown out a significant portion of engine and exhaust noise.

[Never Convicted]

Originally Posted by Red Bread

I've always wondered how much integrity there is in redline display? Since BMW fudges (for legal reasons) the speedo, are the tachs honest? I know dynos report the honest number, but are they always directly correlated to the indicated tachometer? Could BMW just say the F8x redlines at 7700 rpm, paint the redline there and have the engine only turn over 7400 rpm at that point, or would the moon just instantly collide with the earth, kill all mankind and doom us all?

My God, I hope not. At least til the end of my lease.

[ramuman]

Originally Posted by positiveions

I want to say ,realistically, it's more like 7500 rpm.

swamp does the analysis, the head of BMW M says it'll be close to 8k, yet your gut feeling is the realistic one?

[M3_WC]

7,700 is worlds apart from 8,300.

[bimmerjph]

Originally Posted by Red Bread

Could BMW just say the F8x redlines at 7700 rpm, paint the redline there and have the engine only turn over 7400 rpm at that point, or would the moon just instantly collide with the earth, kill all mankind and doom us all?

It would certainly seem like it on this forum if they did that.

[aajami]

Originally Posted by M3_WC

7,700 is worlds apart from 8,300.

Agreed. RPMs become like the Richter scale at some point -- every 100RPMs above 7,500 is an exponential increase over the previous.

*This is all figuratively speaking, mind you.

[Boss330]

Originally Posted by M3_WC

7,700 is worlds apart from 8,300.

No, it's only 600rpm apart... Or 7,8%

Hardly worlds apart...

The E30 M3 S14 engine had a rev limit of 7300rpm

The E36 M3 S50 engine had a rev limit of 7200rpm

The E46 M3 S54 engine had a rev limit of 8000rpm

The E9x M3 S65 engine has a rev limit of 8300rpm

Never heard much complaint about low rev limit on the prevoius straight engine M3's before...

[sparkyg]

Originally Posted by swamp2

Thanks. I wanted to do some more work using actual track clips but did not have the chance. If you can suggest a good, clear redline occurrence for the F10 M5 I would be happy to repeat the analysis. It very quick to do actually, the software does everything.

Swamp2 I dont always agree with everything you write but your technical skills are pretty fckg impressive.

Really nice work.

[Boss330]

Originally Posted by aajami

Agreed. RPMs become like the Richter scale at some point -- every 100RPMs above 7,500 is an exponential increase over the previous.

*This is all figuratively speaking, mind you.

There's not a MAJOR difference between the sound at 7500rpm and 8000rpm on this S54 on the dyno:

Yes, the pitch (frequency) is higher. But it's not like it's the sound of two different engines... IMHO

You would need to be an "expert" to be able to distinguish between the sound this V8 makes at 7500rpm and 8000rpm... (33Hz difference)

[M3_WC]

Originally Posted by Boss330

No, it's only 600rpm apart... Or 7,8%

Ok if you say so.

[RMB]

Dude, all of the analysis stuff makes my head hurt!

[FogCityM3]

Wow..incredible! only on M3 board could you get such innovative thinking and quality content!

[Boss330]

Originally Posted by M3_WC

Ok if you say so.

It's a frequency difference of 30HZ (on a 6cyl engine)... Yes, you can tell, but it's not worlds apart

[Boss330]

Originally Posted by aajami

Agreed. RPMs become like the Richter scale at some point -- every 100RPMs above 7,500 is an exponential increase over the previous.

*This is all figuratively speaking, mind you.

According to Columbia University of New York, it's actually the other way around...

The difference to our ears between 101 Hz and 100 Hz is much greater than the difference between 1,001 Hz and 1,000 Hz. We don’t hear a change of 1 Hz for each; instead we hear a change of 1,001/1,000 (= 1.001) as compared to a much bigger change of 101/100 (= 1.01).

Change in lower frequencies are much more noticeable than changes higher up (surprised me, but makes sense when you think about it).

http://music.columbia.edu/cmc/musica...ter1/01_03.php

[aajami]

Originally Posted by Boss330

According to Columbia University of New York, it's actually the other way around...



Change in lower frequencies are much more noticeable than changes higher up (surprised me, but makes sense when you think about it).

http://music.columbia.edu/cmc/musica...ter1/01_03.php

Hi Boss330,

I appreciate the thoughtful feedback! It's certainly interesting to see the science behind it.

Per my original disclaimer, though, I was referring simply to the emotion of driving a high-revving engine vs. driving one with a lower redline. Or put another way, when I had my S2000, there was a world of difference between how the car felt and sounded (and how both made me feel) when I would hold the RPMs at 7,000 vs. when I'd hold them 8,000 and at 8,900. The same goes for the M3: 7K RPM feels a certain way -- and 8,000 feels like something else altogether.

Source: My unscientific brain.