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      07-25-2013, 01:13 PM   #23
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So, now the question remains, why is it limited and how do we resolve it?

do we know 100% that it is still limiting?
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      07-25-2013, 02:00 PM   #24
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I'm sure it gets to 100% at some point.
It's just that the time you can run at WOT between 6k and 8k is the wink of an eye.
Need something with very high sample rate.

Thanks for the verification, seank.
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      07-25-2013, 02:12 PM   #25
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I also tried in sport mode and got the same result. We don't know that the throttle bodies aren't 100 percent open which is the important part.
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      09-04-2021, 04:10 PM   #26
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I know this is an old topic, but did we ever determine why the throttle is only opening up to ~75%? And limited to values less than this under low rpm/ high load conditions?
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      09-04-2021, 08:23 PM   #27
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Certain BMW software versions seem to do this, but others do not. It can also be related to the torque limiters in the ECU.
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      11-17-2021, 06:34 PM   #28
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Lets not forget about the oil pressurizing the Vanos system... thats at about 4500-5000 rpm. Were talking about 1400 psi! Its not all about throttle plate opening.
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      02-13-2022, 01:30 PM   #29
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I've continued to try and find a reason for why throttle output may be capped at ~76%, and I believe I found at least one reason why this may be the case. See link below (I've attached the corresponding paper as well).

http://www.diva-portal.org/smash/get...FULLTEXT01.pdf

See figure 3.2 on page 14. As an approximation of the cross sectional area of throttle opening vs throttle angle, you have a certain degree of accuracy, whether you take into account the throttle body shaft or not up to ~80%. Beyond this, you see that this would begin to diverge.

Note that this figure does not take into account the thickness of the blade (which would introduce even more error into this plot). This paper also describes how to approximate that error based on throttle plate thickness with respect to throttle angle. If/when you take into account the thickness of the plate, this would seem to very nearly line up with what we're seeing here.

Without being able to see/understand the code myself within MSS70, this is a bit speculative in terms of why the limit would be at this threshold. But it also stands to reason that BMW engineers may have capped this so as to minimize the amount of propagating error for any corresponding calculations/references used to control ECU logic alongside measurements from the MAF itself.

I wouldn't know if what's being seen on data logging is actual TPS position, or if it's 'corrected' TPS position.

As far as torque limiters go, it'd make sense that any artificial limitation of throttle opening <76% at the low end would apply, but without knowing the exact torque limiter threshold vs. what the engine actually is outputting, its difficult to understand if this also applies when the throttle reaches the 76% value or not.
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File Type: pdf Flow Through a Throttle Body.pdf (1.53 MB, 55 views)
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      10-21-2022, 07:32 AM   #30
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Following up on this: Yes, MSS70 has a torque limiter that prevents the throttle opening beyond a certain percentage below 4200 rpm. Yes, it can be defeated. Maximum throttle plate angle is actually 85%. At around 2000 rpm, it's limited to around 40%.

This limiter is active regardless of whether the ECU is running a MAF-based tune or alpha-n tune.

I spent some time testing various versions of MSS70 software and eventually found the tables responsible for the limited throttle at low rpm. I'm going to be hitting the dyno soon to see what sort of power improvements we can expect. FWIW, I haven't ever seen these tables modified before, and they aren't straightforward to find or tune. I'm optimistic about the improvement to low-end torque. If all works out, I'm going to have to go back to every MSS70 customer I've ever had and revise their tune

I've attached a screenshot of data logs that show the torque limiter's effect on the throttle opening. These logs were taken from the same car using two different tunes- one with the torque limiter in place and one with it deleted. You can also data log your own Z4M and see what I'm describing firsthand.
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      10-22-2022, 03:43 AM   #31
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Very interesting. You've done a lot of great work on the ecu already. Is this limitation of the throttle at low rpm different than other torque limits you've seen within the mss70 ecu? If yes, it's odd that they'd have two different locations /types of limits implemented. If the mss54 doesn't have similar limitations in place, it may be related to bmw just wanting the artificially slow the z4m down?

Is what you describe above just for first gear, or for any gear?
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      10-22-2022, 09:21 AM   #32
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Wow, great find! Drivetrain preservation is my guess for why it's there.
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      10-22-2022, 09:51 AM   #33
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Awesome work Josh, just wondering... does the traction control have an input on this , as with it off, there def aint a loss of torque when you plant your foot.. or maybe traction only pulls fueling/timing? (or is it brake operated only, which i doubt as i only have independent brakes these days, not car controlled/augmented)

I ask, as i was doing runs up and down the street the other day , and initially though the car was down on power in 3rd, (after easily doing full 3rd gear rolling burnouts) as it was struggling to break traction(in 3rd), but only to discover later on that traction was actually on, while previous runs it wasnt.
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      10-23-2022, 01:41 AM   #34
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Quote:
Originally Posted by E86Z4MC View Post
Very interesting. You've done a lot of great work on the ecu already. Is this limitation of the throttle at low rpm different than other torque limits you've seen within the mss70 ecu? If yes, it's odd that they'd have two different locations /types of limits implemented. If the mss54 doesn't have similar limitations in place, it may be related to bmw just wanting the artificially slow the z4m down?
It's very different from the others. I have the Siemens MSx70 Funktionsrahmen, and this specific limiter isn't mentioned at all. I'm certain it was added by BMW after the ECU was developed as a proprietary customer addition.

The types of torque limiters in MSS70 are found in several different forms, including a "target" torque that will open/close the throttle body to make the airflow match the desired torque, and a "not to exceed" torque which is sort of like a hard limit. The ECU also has acceleration limiters by speed. This one is completely different from the others in that it's not related to calculated airflow.

Quote:
Originally Posted by E86Z4MC View Post
Is what you describe above just for first gear, or for any gear?
This limiter is present in every gear. You can try data logging your car to see what I mean. If you accelerate from 2000 rpm, the TPS will gradually increase from 40% to 85% by 4200 rpm.
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      10-23-2022, 01:44 AM   #35
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Quote:
Originally Posted by wdb View Post
Wow, great find! Drivetrain preservation is my guess for why it's there.
I think this is one reason why it's there. We've increased torque by 75% over stock and not run into any issues other than the clutch slipping, so I think BMW was being conservative. They also didn't want the Z4M to smoke the M3.
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      10-23-2022, 01:45 AM   #36
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Quote:
Originally Posted by Vanne View Post
Awesome work Josh, just wondering... does the traction control have an input on this , as with it off, there def aint a loss of torque when you plant your foot.. or maybe traction only pulls fueling/timing? (or is it brake operated only, which i doubt as i only have independent brakes these days, not car controlled/augmented)

I ask, as i was doing runs up and down the street the other day , and initially though the car was down on power in 3rd, (after easily doing full 3rd gear rolling burnouts) as it was struggling to break traction(in 3rd), but only to discover later on that traction was actually on, while previous runs it wasnt.
Wait until I disable this limiter... then you will need even more tire out back

Traction control can pull fuel, timing, and close the throttle body to limit torque.
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      11-02-2022, 08:10 PM   #37
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Any update on dyno testing and data logging to quantify improvement of this? Most interested in understanding torque curve, air flow rate and accelerator and throttle position and rpm.

Anyone with an e46 m3 that could provide similar data (preferably stock)?
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      11-05-2022, 08:38 AM   #38
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Quote:
Originally Posted by E86Z4MC View Post
Any update on dyno testing and data logging to quantify improvement of this? Most interested in understanding torque curve, air flow rate and accelerator and throttle position and rpm.

Anyone with an e46 m3 that could provide similar data (preferably stock)?
The logs posted above show most of what you've requested. Airflow and load in mg/stk and N-m are calculated based on lookup tables and can be artificially influenced to skew results. Power at the wheels is the main area where we will see improvements (if they exist). I have a dyno session booked next week where I plan to test before/after on the same car, same day.
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      11-12-2022, 10:44 AM   #39
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Good news/ bad news. The good news is that removing the limiter made a big difference. The bad news is that the difference was so big that the engine started breaking up and misfiring on the dyno. This is likely due to the airflow tables not being tuned to support the extra air. We had a long dyno session ahead of us; the customer did not care about power below 4000 rpm (track car); and the customer was paying for the time... so we had to move on to tuning other things. I'll revisit when I get someone interested in testing.
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      11-13-2022, 06:35 AM   #40
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When you say big difference, what metric and how much?

Also, does the e46 s54 have the same limiter at low rpm?
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      11-14-2022, 05:06 PM   #41
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Quote:
Originally Posted by pokeybritches View Post
the difference was so big that the engine started breaking up and misfiring on the dyno.
This is the metric... so much extra airflow that the fuel trims could not keep up. The E46 M3 does not have a limiter of the same name, although it may have a different limiter. I have not looked further into it.
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      06-11-2023, 03:32 PM   #42
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Quote:
Originally Posted by E86Z4MC View Post
Anyone with an e46 m3 that could provide similar data (preferably stock)?
Old thread, but on the E46 M3, the situation is this:

US cars: Throttle limited to 70% until 4k RPM. Two maps that control this

Euro cars: Limited to 90% until ~2.5k, 100% thereafter. Two maps still present, but the second ("global") map is unrestricted. CSL is similar, except 95%.

I haven not investigated Euro vs US Z4M software.

I'm not sure what the rationale for the US limitation is on the M3. I do recall when I've driven US header cars on CSL software, hitting WOT at low revs can cause some serious bucking that isn't present on Euro header cars, perhaps the throttle limit was their mitigation for that - though I can't really explain why that behavior would exist
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