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      04-21-2017, 11:49 AM   #1
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M4cs Power output analysis - This S55 variant is quite potent

I originally posted this in the M4cs thread, but decided to start a separate thread in the engine section for a more in depth technical discussion. The S55 variant in the M4cs seems to be quite potent. Much more so than the modest 10hp peak increase over the CP suggests.

I had a little fun plotting the base and Comp Pack rated power curves over the CS (preliminary) rated power curve. It is interesting to see that the CS provides substantially more area under the curve over the CP compared to what the CP provides over the base S55; and this despite having half the peak gain (10hp vs 19hp). That is what 37lb-ft of extra torque does for you . It should make the CS quite quicker than the CP and even more so than the base M3/4. It's also interesting to notice the CS has less power than the CP and base S55 below ~2300RPM. I wonder what changes were made to the engine? Is this the result solely from a different tune?

EDIT (Nov-2017)
On a quiet, cold and rainy Sunday afternoon, I had a little time to kill. So I set out to capture test results from European publications (mostly German) for acceleration to compare the different M4 variants. To remove the effect of the added grip at launch provided by PSC2 when the cars are so fitted, I only set out to capture the 100 to 200km/h acceleration. I compiled 21 different tests and then averaged the results for each M4 variant (DCT only). While this is not the most scientific approach, it does provide a decent perspective. Here are the results:

100km/h -> 200km/h acceleration
9.52 M4 Base (6 samples)
.... ∆ 0.20
9.32 M4 CP (9 samples)
.... ∆ 0.67
8.65 M4 cs (4 samples)
.... ∆ 0.20
8.45 M4 GTS (2 samples)

First, I think this dispels the rumours that the CP is not any quicker than the base model, having a ~0.2 second advantage from 100 to 200km/h. Second, it also shows how the CS pulls quite strongly in the top end, being ~0.7 seconds faster than the CP and only ~0.2 seconds short of the mighty water injected GTS. Which is in line with the conclusion reached when looking at the power charts .

CS in black, CP in red, base S55 in blue:
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      04-21-2017, 12:02 PM   #2
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Quote:
Originally Posted by CanAutM3 View Post
I originally posted this in the M4CS thread, but decided to start a separate thread in the engine section for a more in depth technical discussion. The S55 variant in the M4CS seems to be quite potent. Much more so than the modest 10hp peak increase over the CP suggests.

I had a little fun plotting the Comp Pack rated power curve over the CS (preliminary) rated power curve. It is interesting to see that the CS provides substantially more area under the curve over the CP compared to what the CP provides over the base S55; and this despite having half the peak gain (10hp vs 19hp). That is what 37lb-ft of extra torque does for you . It should make the CS quite quicker than the CP and even more so than the base M3/4. It's also interesting to notice the CS has less power than the CP and base S55 below ~2300RPM. I wonder what changes were made to the engine? Is this the result solely from a different tune?

CS in black, CP in red, base S55 in blue:
With all due respect, and I know you're enjoying the analysis of the CS, you can derive almost zero conclusion from overlaying the gimmicky Excel graph outputs that BMW publishes in its marketing materials.
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      04-21-2017, 02:00 PM   #3
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Quote:
Originally Posted by Sleeper View Post
With all due respect, and I know you're enjoying the analysis of the CS, you can derive almost zero conclusion from overlaying the gimmicky Excel graph outputs that BMW publishes in its marketing materials.
Your statement tells me you don't know much about engine testing and how official manufacturer ratings are obtained
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      04-21-2017, 02:04 PM   #4
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Quote:
Originally Posted by CanAutM3 View Post
Quote:
Originally Posted by Sleeper View Post
With all due respect, and I know you're enjoying the analysis of the CS, you can derive almost zero conclusion from overlaying the gimmicky Excel graph outputs that BMW publishes in its marketing materials.
Your statement tells me you don't know much about engine testing and how official manufacturer ratings are obtained
Yes, because the data BMW has published respecting the S55's power output has reflected reality. Enjoy your comparisons .
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      04-21-2017, 02:05 PM   #5
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Knowing what we now know about the S55 now, they're just running more boost and maybe some overlap changes @ Peak VE to get that extra power under the curve.

I'm not sure why BMW didn't just reuse the water Injection from the GTS, TBH.
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      04-21-2017, 02:12 PM   #6
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Interesting analysis of the 3 variants. I also think its important to note the flat power curve for the CS model. Doesn't seem to peak like the CP.
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      04-22-2017, 12:22 PM   #7
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Quote:
Originally Posted by Sleeper View Post
With all due respect, and I know you're enjoying the analysis of the CS, you can derive almost zero conclusion from overlaying the gimmicky Excel graph outputs that BMW publishes in its marketing materials.
Someone always has to argue with the engineer....
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      04-23-2017, 07:01 AM   #8
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Quote:
Originally Posted by CaryTheLabelGuy View Post
Knowing what we now know about the S55 now, they're just running more boost and maybe some overlap changes @ Peak VE to get that extra power under the curve.
That was my original thought. But then seeing the power drop below 2300RPM got me thinking something was done to the turbos.

Quote:
Originally Posted by CaryTheLabelGuy View Post
I'm not sure why BMW didn't just reuse the water Injection from the GTS, TBH.
I agree. I certainly had wished for that

Further, did you notice that in the press releases they talk about a lightweight magnesium oil sump?
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      04-23-2017, 07:49 AM   #9
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Quote:
Originally Posted by CanAutM3 View Post
That was my original thought. But then seeing the power drop below 2300RPM got me thinking something was done to the turbos.



I agree. I certainly had wished fir that

Further, did you notice that in the press releases they talk about a lightweight magnesium oil sump?
I saw that slight dip in power below 2300rpm, but I'm not sure what to make of that. It's possible they did something to the turbos, but I doubt it because the boost appears to taper off at the same point. Larger turbos would have less boost taper up-top unless BMW specifically dropped boost targets more up-top to keep power down?

As for the magnesium oil sump, I must have totally missed that as I didn't see it. I need to go back and read that press release again.
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      04-23-2017, 08:09 AM   #10
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Quote:
Originally Posted by CaryTheLabelGuy View Post
I saw that slight dip in power below 2300rpm, but I'm not sure what to make of that.
It's a fairly subtantial drop in power at low RPM: ~50 less hp at 1900 RPM. That's 35% less.

Quote:
Originally Posted by CaryTheLabelGuy View Post
As for the magnesium oil sump, I must have totally missed that as I didn't see it. I need to go back and read that press release again.
About midway in the 4th paragraph of the engine section in the "long version" of the press release.
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      04-23-2017, 09:55 AM   #11
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I saw that but assumed that they were referring to the S55 engine in general rather than the CS variant. Didn't the early S55 come with a magnesium oil pan ? (happy to be corrected if it didn't). And what about the extra oil suction pump ? Does the CS variant actually have an extra oil pump or, again, are they talking about the S55 in general ?
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      04-23-2017, 01:00 PM   #12
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Quote:
Originally Posted by SO17 View Post
I saw that but assumed that they were referring to the S55 engine in general rather than the CS variant. Didn't the early S55 come with a magnesium oil pan ? (happy to be corrected if it didn't). And what about the extra oil suction pump ? Does the CS variant actually have an extra oil pump or, again, are they talking about the S55 in general ?
Yes, the S55 did come with a Mg oil pan at launch, but it was replaced with an Al oil pan after the first year. I was surprised to see the Mg oil pan announced again for the CS.
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      04-24-2017, 08:47 AM   #13
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So the "hardware" between all these variants are pretty much the same?, just software tweaks?
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      04-24-2017, 08:50 AM   #14
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Quote:
Originally Posted by JoeyBananas View Post
So the "hardware" between all these variants are pretty much the same?, just software tweaks?
That is the point of the discussion? We don't know for sure yet. It would be much cheaper for BMW to make through software only.

But I wonder why they would have purposefully reduced the low end-power on the CS by so much if it were through software only ??
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      04-24-2017, 01:53 PM   #15
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BMW just plays with the timing and boost control and fine tunes the engine map even more.
Maybe the stepper motor on the boost control is even finer resolution.

I bet you in a year or so some tuner will offer the update for the ECU for all cars...
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      04-24-2017, 03:36 PM   #16
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Quote:
Originally Posted by stevehifi View Post
BMW just plays with the timing and boost control and fine tunes the engine map even more.
Maybe the stepper motor on the boost control is even finer resolution.

I bet you in a year or so some tuner will offer the update for the ECU for all cars...
Why would BMW REDUCE the power below 2300RPM on the CS engine if it is only from a change of tune ?
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      04-24-2017, 05:46 PM   #17
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Quote:
Originally Posted by CanAutM3 View Post
Why would BMW REDUCE the power below 2300RPM on the CS engine if it is only from a change of tune ?
My guess would be to allow better hookup during the lower rpms, but I think that job should be handled by the Cups and the tweaked suspension with ease.

That is the only logical reason I can come up with.
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      04-24-2017, 05:46 PM   #18
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Quote:
Originally Posted by stevehifi View Post
BMW just plays with the timing and boost control and fine tunes the engine map even more.
Maybe the stepper motor on the boost control is even finer resolution.

I bet you in a year or so some tuner will offer the update for the ECU for all cars...
There would be no point. Stage 1 flash tunes already exceed the performance of all factory available tunes for the S55. For the majority of people, if you're splitting your DME case, you're not going to go with a mild OEM upgrade. VF offers a ZCP-style/performance map, but I can't imagine the uptake on that is very high when the cost for the much more significant performance bump (Stage 1) is marginal.
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      04-24-2017, 06:47 PM   #19
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Quote:
Originally Posted by bd307 View Post
My guess would be to allow better hookup during the lower rpms, but I think that job should be handled by the Cups and the tweaked suspension with ease.

That is the only logical reason I can come up with.
You're reading too much into the marketing 'power' graph that BMW publishes.. it's a gross representation of the engine power curve and each motor varies over production tolerances. Best thing to do is wait until someone actually dynos a CS and then you can see the differences...
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      04-24-2017, 07:02 PM   #20
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Quote:
Originally Posted by stevehifi View Post
You're reading too much into the marketing 'power' graph that BMW publishes.. it's a gross representation of the engine power curve and each motor varies over production tolerances. Best thing to do is wait until someone actually dynos a CS and then you can see the differences...
Those power charts are likely coming from the testing BMW did to obtain their certified rating. They are most probably more precise and repeatable than any chassis dyno run done at the corner shop.

The challenge with modern engines, particularly forced induction ones, is that they can produce more power when in transient than in steady state, giving the impression that they are "underrated" from the factory.
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      11-05-2017, 04:44 PM   #21
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On this quiet, cold and rainy Sunday afternoon, I had a little time to kill. So I set out to capture test results from European publications (mostly German) for acceleration to compare the different M4 variants. To remove the effect of the added grip at launch provided by PSC2 when the cars are so fitted, I only set out to capture the 100 to 200km/h acceleration. I compiled 21 different tests and then averaged the results for each M4 variant (DCT only). While this is not the most scientific approach, it does provide a decent perspective. Here are the results:

100km/h - 200km/h acceleration
9.52 M4 Base (6 samples)
.... ∆ 0.20
9.32 M4 CP (9 samples)
.... ∆ 0.67
8.65 M4 CS (4 samples)
.... ∆ 0.20
8.45 M4 GTS (2 samples)

First, I think this dispels the rumours that the CP is not any quicker than the base model, having a ~0.2 second advantage from 100 to 200km/h. Second, it also shows how the CS pulls quite strongly in the top end, being ~0.7 seconds faster than the CP and only ~0.2 seconds short of the mighty water injected GTS. Which is in line with the conclusion reached in the OP when looking at the power charts .
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      11-05-2017, 04:56 PM   #22
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Are you trying to justify your soon to be purchased CS?

Would be nice to see the GTS also plotted on that graph.
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