M4cs Power output analysis - This S55 variant is quite potent

[CanAutM3]

Originally Posted by melvyn

Your a nit picker sir

S55 engine will rev up to 7600 as states in your image

CP redlines at 7500 revs
CS redlines at 7600 revs

Yes or no?

IMO, no. The "redline" is where the red zone starts on the tacho. From that perspective, the CP and CS both have the same 7500RPM "redline". Now, what could be different is the maximum engine speed, where the rev limiter kicks in. But as far as I know, all S55 variants in the M3/4 share the same 7600RPM rev limiter (maximum engine speed).

Originally Posted by melvyn

Info for you

CS

https://www.gtplanet.net/forum/threa...s-2017.369734/

CP

https://www.gtplanet.net/forum/threa...e-2016.341563/

You can apologize next time I come on.

Enjoy your motor, it really is a special piece of kit out of the box

I am not sure I would trust a video game website as a reliable source of automotive technical details .

I think there is a fair bit of confusion in general in the press about redline and max engine speed. However, I don't recall reading anything in the official BMW documentation relating to an increase of maximum engine speed for the M3/4 CS.

Originally Posted by melvyn

Yep, 7700

That's is indeed news to me. What is your source?

[CanAutM3]

Originally Posted by EricSMG

Thanks for this but it's starting to look like the CS falls off more sharply as you approach red line even though it's making more power until the CP regains the advantage at ~7250rpm (however small this might be - the real world this will be moot).

I was hoping that the CS held a flat HP line right up to/near the limiter. Now, I'm not taking anything away from the CS, I just assumed it would have more of a 'racing' dyno curve. No doubt the area under the curve is impressive, though. I'm wondering how much of that area is possible with 91 octane fuel, above an beyond the CP on the same fuel.

I don't believe the CP ever "regains the advantage". The CS makes more power up to ~7200RPM and then matches the CP to redline, as per BMW official ratings.

[EricSMG]

Originally Posted by CanAutM3

I don't believe the CP ever "regains the advantage". The CS makes more power up to ~7200RPM and then matches the CP to redline, as per BMW official ratings.

I was only referring to the (fuzzy) graph you posted which shows the CP holding flat (and slightly higher) past about 7250rpm.

But that's not my point, which is that the CS falls at a steeper slope as max engine speed is approached. This might be why Melvyn is suggesting the early shift point - based on the shape of the CS' high rpm HP slope, it's obvious that the HP drop after ~6.5k will be easily felt on the road which is exactly what he's reporting.

Splitting hairs, yes, but it's interesting to see how the CS and CP power curve shapes compare. The CS is obviously much more powerful across the tach, but it may be less rewarding to wind out past 6.5k rpm.

Edit - after looking closer at the graph, both cars have flat HP curves until more like 6750rpm, at which point the CS falls slightly faster. From this, I'm betting it "feels good" up to about 7k but no higher, similar to my CP. Further, at least based on that graph, there is a disconnect with Melvyn suggesting that it falls off sharply starting at 6k - I'm not seeing that but then I'm not driving a broken-in CS either In either case, the CS power curve looks really fun and punchy - I just wonder how tractable that 3k torque spike is in the lower gears.

[M3GymNut]

Originally Posted by CanAutM3

When pot meets kettle...

Who's being negative here . You don't think that you coming into a thread without even reading it and posting that "it is worthless" is trollish, ignorant or hostile?

I don't mind constructive debates at all. I actually seek them and do have an open mind towards them since they improve collective knowledge. However, making blanket negative comments without substance adds zero value to the forum community.

LOL, the irony...your direct negative comments to posters that you disagree with you find them to have substance and have value? Dude, you're blind and on another level. Good luck and enjoy the forums.

[CanAutM3]

Originally Posted by M3GymNut

LOL, the irony...your direct negative comments to posters that you disagree with you find them to have substance and have value? Dude, you're blind and on another level. Good luck and enjoy the forums.

Yes, I do believe that offering a counterpoint backed with either explanations, alternative references or physics equations has substance and adds value. Disagreeing in itself is not a "negative comment".

[CanAutM3]

Originally Posted by EricSMG

That seems backwards as the DCT has much closer ratios which would/should result in a smaller rpm drop between shifts.

Now, I haven't compared the tranny ratios so I could be wrong.

Edit - wait, I'm reading Can's gearing thread. Let me digest that and I'll rephrase my response here.

Edit 2 - that thread doesn't have the ratios listed. Still hunting for those. I'm "ass-uming" that the DCT has much closer gear spacing since it did in the E9XM but that may be incorrect for this chassis.

Contrary to the E9X, the DCT has wider ratios than the 6MT on the F8X:

________DCT________MT
1st____4.806______4.110
2nd____2.593______2.315
3rd____1.701______1.542
4th____1.277______1.179
5th____1.000______1.000
6th____0.844______0.846
7th____0.671

Final
Drive___3.462____3.462

[melvyn]

Originally Posted by CanAutM3

IMO, no. The "redline" is where the red zone starts on the tacho. From that perspective, the CP and CS both have the same 7500RPM "redline". Now, what could be different is the maximum engine speed, where the rev limiter kicks in. But as far as I know, all S55 variants in the M3/4 share the same 7600RPM rev limiter (maximum engine speed).



I am not sure I would trust a video game website as a reliable source of automotive technical details .

I think there is a fair bit of confusion in general in the press about redline and max engine speed. However, I don't recall reading anything in the official BMW documentation relating to an increase of maximum engine speed for the M3/4 CS.


That's is indeed news to me. What is your source?

All information about the CS is adamant that the revs have been raised by one hundred.To do that , wouldn't you have to raise the limiter by one hundred.


If the revs were raised to 7600 on the CS, then surely the limiter would have to be raised one hundred revs or there would be no point in doing it as it would just be the same as you say.
I note that Bootmod 3 also has a function to raise the limiter , to what I do not know.
All a bit confusing.

[CanAutM3]

Originally Posted by melvyn

All information about the CS is adamant that the revs have been raised by one hundred.To do that , wouldn't you have to raise the limiter by one hundred.


If the revs were raised to 7600 on the CS, then surely the limiter would have to be raised one hundred revs or there would be no point in doing it as it would just be the same as you say.
I note that Bootmod 3 also has a function to raise the limiter , to what I do not know.
All a bit confusing.

I searched a fair bit and couldn't find anything to that effect in the BMW AG press material or technical publications. All refer to a maximum engine speed of 7600rpm for all S55 variants. See excerpts below from the original M3/4 press release and M4cs press release.

During my search, I did find some references of a raised engine speed for the CS in British press reviews, but nothing in German publications. I wonder if it is not a misinterpratation of some sort that made its way through. There is no "technical reason" to have the maximum engine speed increased on the CS.

Quite confusing indeed.

[melvyn]

Originally Posted by CanAutM3

I searched a fair bit and couldn't find anything to that effect in the BMW AG press material or technical publications. All refer to a maximum engine speed of 7600rpm for all S55 variants. See excerpts below from the original M3/4 press release and M4cs press release.

During my search, I did find some references of a raised engine speed for the CS in British press reviews, but nothing in German publications. I wonder if it is not a misinterpratation of some sort that made its way through. There is no "technical reason" to have the maximum engine speed increased on the CS.

Quite confusing indeed.

Yes,British press reviews led one to believe it had been increased.They also stated in the BM spec release that the wheels were 9.5 and 10.5 which is false .Ive sent BM an email to confirm the correct data and will report back when I receive a reply in next couple of days.

[CanAutM3]

Originally Posted by melvyn

Yes,British press reviews led one to believe it had been increased.They also stated in the BM spec release that the wheels were 9.5 and 10.5 which is false .Ive sent BM an email to confirm the correct data and will report back when I receive a reply in next couple of days.

Yes, I also recall reading in the BMW UK documentation that the CS have a Titanium exhaust, which is also false. Local BMW distributors are notorious for making mistakes in their publications, BMW USA is particularly bad.

Looking forward to your findings .

[shortseller]

Originally Posted by melvyn

All information about the CS is adamant that the revs have been raised by one hundred.To do that , wouldn't you have to raise the limiter by one hundred.


If the revs were raised to 7600 on the CS, then surely the limiter would have to be raised one hundred revs or there would be no point in doing it as it would just be the same as you say.
I note that Bootmod 3 also has a function to raise the limiter , to what I do not know.
All a bit confusing.

BPMsport advertises they offer a raise rev limiter increase +200 rpms as an added option if one buys their sw upgrades, which included CS and GTS maps.

[melvyn]

Originally Posted by shortseller

BPMsport advertises they offer a raise rev limiter increase +200 rpms as an added option if one buys their sw upgrades, which included CS and GTS maps.

Thanks, will take a look at that

[mechanic75]

For scientific purposes today I checked this out...redline is 7500 but cut out was definitely higher. Hard to tell but I’d say 7600.

Pulled pretty hard there too. Second gear.

[CanAutM3]

Originally Posted by EricSMG

I was only referring to the (fuzzy) graph you posted which shows the CP holding flat (and slightly higher) past about 7250rpm.

But that's not my point, which is that the CS falls at a steeper slope as max engine speed is approached. This might be why Melvyn is suggesting the early shift point - based on the shape of the CS' high rpm HP slope, it's obvious that the HP drop after ~6.5k will be easily felt on the road which is exactly what he's reporting.

Splitting hairs, yes, but it's interesting to see how the CS and CP power curve shapes compare. The CS is obviously much more powerful across the tach, but it may be less rewarding to wind out past 6.5k rpm.

Edit - after looking closer at the graph, both cars have flat HP curves until more like 6750rpm, at which point the CS falls slightly faster. From this, I'm betting it "feels good" up to about 7k but no higher, similar to my CP. Further, at least based on that graph, there is a disconnect with Melvyn suggesting that it falls off sharply starting at 6k - I'm not seeing that but then I'm not driving a broken-in CS either In either case, the CS power curve looks really fun and punchy - I just wonder how tractable that 3k torque spike is in the lower gears.

I agree with what you are saying, as with all S55 variants, there is no need to wring the engine to redline in the upper gears (3rd and up) to extract maximum acceleration. I'd say the power band sweet spot seems to be between 5200rpm and 7000rpm. Only 1st and 2nd need redline shifts.

The torque swell around 3000rpm displayed on the cassis dynos is a bit surprising, as BMW claim peak torque is not achieved until 4000rpm. In real life the car is quite tractable. The power builds very progressively from 1200rpm to 3000rpm. It almost feels like a NA engine in the way it build up power. I have to admit I kinda miss the massive low RPM push of the early S55 tune, particularly when just cruising on the highway in 7th gear, power is just a downshift away though.

BTW, I found a less fuzzy graph of the BPM dyno pull between the baseline and CS tunes (albeit it includes their own custom tune also). Looking at the shape of the “baseline” tune would have me believe it is of a “base 425hp” tune and not the CP tune though.

[melvyn]

Can confirm limiter is set at 7600 on CS, so why BM made such a bump about the revs being upped to 7600 is beyond me ,as it's quite normal to have 100 revs above the redline to limiter.

[CanAutM3]

Originally Posted by melvyn

Can confirm limiter is set at 7600 on CS, so why BM made such a bump about the revs being upped to 7600 is beyond me, as it's quite normal to have 100 revs above the redline to limiter.

That's the thing, as far as I know, BMW never made any claims to an increased engine speed for the CS. I am not sure how the confusion came about in the press (mostly the British one).

[melvyn]

Originally Posted by CanAutM3

That's the thing, as far as I know, BMW never made any claims to an increased engine speed for the CS. I am not sure how the confusion came about in the press (mostly the British one).

Yep, every British review pretty much states increased engine revs to 7600, you naturally assume the limiter is another 100 revs above.
Anyway that's that cleared up

[overlook637]

If you look through the maps using the BM3 editor they show 7600rpm and 7500rpm as the end for either the x or y axis plotting for various maps. exhaust flap map is 7600rpm timing maps are 7500rpm

[overlook637]

Originally Posted by CanAutM3

6 years of applied and science and engineering will have me disagree here. Torque at the crank is irrelevant to establish acceleration potential without considering gear ratios. To maximize acceleration at any given road speed, you need to maximize power at that speed. The formula is "a = P/mv" where "a" is acceleration, "P" is power, "m" is vehicle mass and "v" is vehicle speed. Lowering the revs below the power plateau (below 5500RPM) will not yield optimal acceleration, it's physics.

In the same way, redlining every gear is also not optimal (1st and 2nd need to be redlined, but not the others), as the power drops off past 7200RPM to a point the the engine make more power in the higher gear.

Correct.

Many people like to dyno race, in that they think a dyno chart makes a car fast. Forgetting about the transmission that has gears with ratios that alter the engine power before reaching the ground.

There are a few websites that allow people to enter the gear, final drive, and tire size then match the dyno chart results. The results show the true amount of torque/power that is reaching the ground. Many will also plot out the best shift rpms.

[CanAutM3]

Originally Posted by overlook637

Correct.

Many people like to dyno race, in that they think a dyno chart makes a car fast. Forgetting about the transmission that has gears with ratios that alter the engine power before reaching the ground.

There are a few websites that allow people to enter the gear, final drive, and tire size then match the dyno chart results. The results show the true amount of torque/power that is reaching the ground. Many will also plot out the best shift rpms.

Sorry to nitpick, but in general terms, gear ratio do not affect the level of power being transmitted between "the engine and the ground". Gear ratios alter the torque and rotational speed, but the power being transmitted remains the same.

[mechanic75]

I have not driven a standard car so can’t comment. The CS has more mid range than the CP as we know but controversially I think I prefer the power delivery of the CP when pushing on. On B road twisties.

It feels more linear to me and doesn’t have that wall of torque when you come back on the throttle. Easier to modulate. If the CS is akin to the GTS power delivery it would make sense why many road testers struggled with it in certain conditions and on certain road types.

[shortseller]

Originally Posted by mechanic75

I have not driven a standard car so can’t comment. The CS has more mid range than the CP as we know but controversially I think I prefer the power delivery of the CP when pushing on. On B road twisties.

It feels more linear to me and doesn’t have that wall of torque when you come back on the throttle. Easier to modulate. If the CS is akin to the GTS power delivery it would make sense why many road testers struggled with it in certain conditions and on certain road types.

I too prefer a more linear power band and the CP seems to have delivered that to me based on what I had with my non CP 2015. But pretty sure most reviewers I’ve read seem to really like the CS variant the best of all the F series Ms, Joe Achilles comes to mind off the top of my head, even over the 2018 CP he did beforehand(where he was having major traction issues). But he did say the CP with a set of correct tires would be extremely close enough to consider if one wanted to save the money. So many might argue the CP is the sweet spot in the variants.