03-29-2020, 12:10 AM | #45 |
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Here is 2nd to 3rd to 4th log from earlier in the week when I was first testing a new map from proTUNING Freaks. At this point I was shifting at my normal speed of about 1.4 seconds. Same map as my previous post, the only difference being shift speed: https://www.bootmod3.net/log?id=5e7a...0b43508e6fe7fd
This time, the waste gate doesn't close fully for some period after I'm back on the pedal. In the log shown above, the delay between pedal going to 100% and waste gate going to 100% is 0.8 seconds for the 2nd to 3rd shift, and 0.7 in the 3rd to 4th shift. The duration between pedal going to 0% for the start of the shift and the waste gate going to 100% is 1.8 seconds for both shifts. Interestingly, I've gone through all 16 logs that I took with this latest map, and the duration between first lifting the pedal to make the shift and the waste gate going back into controlling boost (which usually means closing) is consistently ~1.8 seconds!
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03-29-2020, 12:26 AM | #46 |
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Here is a log showing quick (< 0.7s) shifts from 2nd to 3rd to 4th. Again, same map, only difference is shift speed: https://www.bootmod3.net/log?id=5e7a...0b43508e6fe39e
This time the delay between pedal at 100% and waste gate going above 80% is 1.1 seconds in both cases - longer than when I shifted slower. The duration between pedal going to 0% for the start of the shift and the waste gate going above 80% is 1.7 seconds In this case, the waste gate never goes to 100% in either shift because boost is already rising fast enough at the point where the waste gate starts to behave normally again. There is a visible bump in the WGDC trace though, which shows that something is going on. Finally, a log here that shows no waste gate bump at all - the effect is totally masked, because the shift was fast enough and the revs high enough that boost didn't drop enough for the wastage to need to be closed by the time it was operating normally again. You still see the bump on the 3rd to 4th shift, but not at all on the 2nd to 3rd: https://www.bootmod3.net/log?id=5e7a...0b43508e6fe3b4
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03-29-2020, 12:36 AM | #47 |
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What does all of this mean for performance though...
Comparing the logs from the >2.0 seconds shifts to the ~1.4 second shifts and the < 0.7 second shifts, the speed at which boost rises is quite different. In the slow shift log, boost has fallen to zero, there is even a vacuum at the MAP sensor, but the waste gate closes fully and boost builds from 0 to meet the target in just 1.4 seconds. In the quicker shift log, the boost build is the same at 1.4 seconds, but boost wasn't at zero... it started from 3.3 psi; a slower boost build with a much faster shift. In the fastest shift log, boost crosses the target in 1.3 seconds, and in this case, boost had only dropped to 5.8 psi; a much higher starting point but basically the same duration for boost to build!
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03-29-2020, 04:46 AM | #48 |
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Nezil, I've dug a bit more and my theory is this:
During shifts, if anything, the ECU is trying to SLOW DOWN the turbine when you think you need it more. Because: 1) Although DV dumps boost, the turbo shaft speed is still high. It's already high enough to support top end charge air (check MAF) which is too much for next gear. 2) The dumped (via DV) charge air goes into turbine housing, adding more pressure. I'm not sure if BMW uses turbo shaft speed sensor though I know for sure Nissan does with the great VQ30. ECU simply decides 80+% is the maximum WG duty to give when you need to SLOW DOWN the turbine, or there'd too much overshoot to deal with after boost target is met. As RPM rises and turbine slows down, it gets to a point where turbine is not overloaded (for the RPM). Then 100% WG duty is allowed. I do not think 80% makes a much slower spool up unlike what you see from your log. It could be the DV working in conjunction on 100% duty when allowed. I've been logging boost behavior on DCT shift for a long time, because it plays a key role in acceleration and safety. My finding is that overshoot is a much more serious issue and takes 500-1000 RPM normally to settle. More boost headroom you leave, more poised the engine will be taking it up, hence the less power loss or you even make more power (by properly eating more boost!). Halim has a "boost guideline" tuning strategy (I made up that name and won't go deeper on it), with that there are even more uncertainties. In any cases, the priority on shift is always boost dumping and turbine adjusting/decreasing. There is no way for 100% WG duty instantly on tap, unless you're already significantly under-boost before shift, which would be a much more horrible scenario. In this sense, to "fix the lag" will be on less pedal down time. DCT fixes it by shifting impossibly fast, not by forcing 100% WG duty.
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03-29-2020, 09:09 PM | #49 | |
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So, if I understand you correctly, there is no fix for a 6MT car if this is designed in to prevent boost overshoot? Could you lower the boost or torque target so the overshoot is safe? I know you might then be leaving power on the table, but at least you wouldn't "feel" the lag? |
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03-29-2020, 09:41 PM | #50 | |||||||
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First off SeanWRT, thank you so much for giving your opinion. I know you've said previously that you don't have much experience with 6MT, but you do have a lot of experience reading logs and understanding how our DME works - and that is super valuable!
The other thing I want to thank you for is having a second opinion. I've been looking at logs since going with BM3 (as you know), and I've got my own opinions about what's going on, but without anyone to bounce these ideas and opinions off, it's very difficult to make any progress. Quote:
Assuming the shaft speed is too fast, are you suggesting that the waste gate is effectively letting the turbine free-wheel a bit to avoid a shock which would slow it down if the waste-gate were to close? Quote:
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03-29-2020, 10:45 PM | #51 |
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I went back and looked at logs again re. boost build speed. Here are the results:
Some caveats though... Boost building isn't a linear effect. The gradient (psi of boost built / second) isn't an exact representation of the speed boost builds in each case, but it is an indication. As you can see, the absolute duration that boost builds for before crossing boost target is longer if you shift slower, but the rate at which boost builds is faster. A faster shift is undoubtably quicker overall, but it could be quicker still if there is some way of speeding up the boost build rate by closing the waste gate. If there is some way of building boost quicker, the biggest effect will be found with reasonably fast shifts ~1.4 seconds. I firmly believe that shifting at 1.4 seconds should be considered a 'fast' shift. It's not super aggressive, but it's also not slow. A 0.7s shift, while possible, is not comfortable for passengers or for the drivetrain. Those of you with 6MT that can capture logs, take a look at your shift times. I'd be surprised if anyone can make shifts quicker than 1.0s on the street day to day.
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03-30-2020, 06:02 AM | #52 |
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Nezil, thanks for taking time on my reply.
By referring to MAF, I was not saying it's high during shifts (because of DV and throttle intervention). Instead I wanted to tell the flow difference at top end and middle range. And how critical it is for DME to dump flow and adjust turbine on shift where rpm goes down. Flow is turbine speed. Boost is Flow divided by RPM. WG%+RPM = pressure on turbine = the change rate of turbine speed, not turbine speed. DME is backing off WG duty. And not seeing a maxed out WG duty seems to be your frustration. But WG duty doesn't make instant impact. And in this case, with other elements in play, 80% makes minimal difference from 100%, and is not why it's laggy. Either this build-in feature can be defeated or not, you may really want to take a second thought about it...
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04-05-2020, 11:31 AM | #53 |
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On my focus RS, I disconnected the recirc valve controller and ran it straight from manifold pressure. Don’t know if this is possible or would help in this situation but this is just a thought..
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04-05-2020, 04:43 PM | #54 | |||
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The lag feels like some safety precaution especially coupled with the rev hang from 1-2, it becomes truly frustrating. I can't even hardly get the car to chirp the rear end into second most of the time as it's so far off power. I have noticed it's not nearly as bad in efficient+mdm, if you drive that setting hard it adapts to feel like a big power N/A engine with a huge spool at the bottom of the pedal. It is truly the most satisfying experience for me. Sport plus just makes me mad because of that lag. Makes the car feel jerky and unsmooth. Except for some shifts! Sometimes it's pure bliss and behaves exactly how I know it should and could in s+... but that's rare. It just feels wrong and artificially held back most of the time. |
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04-05-2020, 05:31 PM | #55 |
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There's probably a legitimate reason they tuned the 6spd manual version this way. Maybe to compensate for the variability of different drivers shifting and avoiding an overboost situation. Much easier with the DCT since they know exactly how that will shift.
I'd rather just deal with it by shifting faster/higher revs vs messing around with the wg response. But i'll be happy to watch as others beta test any tuning attempts to fix. |
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04-10-2020, 07:52 AM | #57 | |
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04-10-2020, 10:32 AM | #58 |
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Sorry for the delay everyone... I've found that this whole 'working from home' thing has been far more stressful and far less time for looking in to issues like this.
Actually I'm a bit disappointed with where we got to with PTF. Initial tests showed promise, but didn't really improve much in any significant way. I feel like I've provided quite a lot of data, and a lot of data analysis, and though I was getting new maps initially that must have had some changes, I never found out exactly what these changes were, and it honestly feels like some confusion about what I'm trying to address. I keep hearing the consistent responses of:
What makes this all the more frustrating is that NVM in the UK claim that they have a fix for this, but aren't prepared to do remote tuning. Either they're making a false claim, or they're one of the only tuners that knows what's needed to tune out this waste-gate closing delay. So far, SeanWRT's suggestion that it could be related to turbo shaft speed is the best I've heard, but this isn't what's being suggested by PTF. I really do want to work more on this, and I'll reach out to PTF one more time and see if they're interested, but if not, it might be time to ask some other tuners familiar with this platform and see if they have any insight. SeanWRT, I've heard you say in the past that the throttle response of the N55 is good. Ordinarily I'd agree with you, but between shifts in 6MT is pretty awful. A fast shift can cause nearly an entire second before boost really starts to build again. Technically the throttle is fully open, but the feeling of throttle response is very delayed.
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04-11-2020, 10:22 AM | #59 | |
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04-15-2020, 12:33 AM | #60 |
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So the latest is that PTF has closed my support ticket as resolved, which is disappointing.
I sent some emails and had a phone call this morning to see if I could find any more evidence for this being a known issue and more importantly, if there has ever been evidence of a fix. My phone call was to Pure Turbos, mostly because I have considered upgrading the turbo on my car, but if this waste gate issue cannot be improved, I don't think I'll be bothering. To my surprise, the guy I talked with there said that this has been a known issue since the N54, and present with the N55 and S55 motors. He had a 600whp 6MT N54 based car and couldn't stand the excessive lag between shifts. Since then he's been auto or DCT precisely because of this. He did think that times had changed since his experience however, and felt that there were initially fixes such as the WOT Box, which is an aftermarket No Lift Shift / Two Step piggyback box for 6MT cars, JB4 has a relay based solution, and more recently flash tunes to address the issue. I've now also sent emails to several tuners in the US, basically asking them if they're interested in working on a solution to this problem together. I'm prepared to pay for a custom tune with them, but only if they're able to address this behaviour. As of now, I'm still waiting to hear back from the tuners I've contacted, but will keep this thread updated if I hear anything.
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04-16-2020, 10:43 AM | #62 | |
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I don't think any tuner ever fixed it by now. IMO, there may be some way to force WG close 100% but it wouldn't fix lag.
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04-16-2020, 11:14 AM | #63 | ||
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What I'm talking about is actually a daily drive-ability feature, for when you're driving at 7/10s or 8/10s. Most tuners focus only on 10/10s behaviour, and maybe that is what 90% of their customers care about; it's certainly important. If you're driving at 10/10s, you can shift in 0.7s at redline, and the behaviour I'd like investigated is masked to the point of being not important. It's when you drive at anything less than 10/10s you feel it, and you feel it bad. The reason it's so objectionable isn't because there is lag, it's because of the way the lag feels. If you look at the screen shots I posted, when shifting from 2nd to 3rd, boost does build even with the WG at 80%, but as soon as it shuts, boost builds far more rapidly, and you feel this as a driver and passenger. Since the rate of change is greater on a 2nd to 3rd shift, you feel it far more there than in other gears. If the WG closes 100%, as it does if you slow shifts down to 2 seconds, boosts builds much more progressively and you don't get this sudden surge. It makes the car uncomfortable for passengers and slower than it needs to be. Does that make more sense?
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04-22-2020, 01:30 AM | #64 |
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Waiting to talk to you for a week, registering for this forum is a nightmare.
Here M2 is a $100K car, $50K used for a first generation M2. You're about to drop your 15 years of savings on this car then luckily you learn of all this BS (and the crank hub, got to love that "superior" german engineering). Which no paid shill "journalist" has ever mentioned even though it's present since N54 cars, and nobody on youtube is ever talking about so they don't look stupid with their compromised manual clout mobile in front of the people they are "influencing". If I had the car here are the people that I would talk to in my part of the globe, they have a reputation for being some of the best BMW tuners: Gelashvili Performance (Mr. George Gelashvili) - https://www.geptuned.com - based in Georgia, they do remote tuning when not touring USA THP Solutions (Mr. Zic) - http://thp.solutions/ - based in Croatia, I don't think they remote tune, but worth inquiring about the issue in general |
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04-22-2020, 04:46 AM | #65 | |
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I agree with this. I don't have a log for it, but I switched DSC off the other night and the under 5K gear changes felt like they had ~50-60% less lag (compared to sport+). Nezil This could suggest that the lag is a DSC imposed issue, rather than an DME mapping issue. Perhaps this is a DSC "feature" (e.g. to reduce transmission shock or wheelspin). I will do a log when I can to compare. Last edited by widetyres; 05-02-2020 at 01:49 AM.. |
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04-22-2020, 01:02 PM | #66 |
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Hi all... I haven't been doing nothing on this, but wanted to wait until I had anything meaningful to report before posting.
I've started working with a tuner who has been good enough to look at addressing this behaviour first, before working on a full custom tune for my car. If we're successful, I'll let everyone know, and provide evidence that it's improved or eliminated. If we're not successful, I won't be posting about who I worked with out of respect to them; they will have tried, but I wouldn't want that to be looked at as a reflection of how good they are at tuning for what 90% of customers want. This seems to be a complex issue that PTF were either unwilling to spend time on (and to be fair, I wasn't paying for their time) or unable to fix. I'm still hopeful and optimistic, but conscious that this might take a while.
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