05-01-2013, 11:02 AM | #23 | |
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After considering all this, my guess is that ppk helps reduce perceived lag by making the throttle in general much more responsive, rather than changing the waste gate. Maybe a dyno before/after comparison would shine the most light on this, since WOT runs would surely isolate the turbo lag? From my time with the N55, I'd say turbo lag was non-existent, but maybe if I was driving a MT and did a 6-2 downshift it would be noticeable.
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05-01-2013, 11:37 AM | #24 | |
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twin scroll turbo in pictures
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By splitting the exhaust gasses of the engine into two ports, BMW was able to increase pressure differential accross the blades of the turbine. Because of the larger pressure differential kenetic energy of the gasses can be better utilized. Here is what TIS has to say on the issue:
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05-01-2013, 02:49 PM | #25 | |
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I can see it being a PPK only update...remember, BMW is targeting it for enthusiasts that are willing to spend the $1100-2000 to buy/install. If you're an enthusiast you won't bat an eye about updating the steering that apparently everyone hates...(I actually don't care; my Evo 8 had the most accurate steering I've ever had the joy of driving).
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05-01-2013, 04:47 PM | #27 |
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05-01-2013, 10:17 PM | #28 | |
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Don't get me wrong, I want a change in the steering and have been asking about this since I bought the car. It's the only issue with the car IMHO. Also, I agree the PPK deals with power concerns nicely on a 6MT. No complaints in torque and power on my end.
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05-01-2013, 11:58 PM | #29 | |
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05-02-2013, 01:02 AM | #30 | |
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Specifically, I'd like to read the info on altered waste gate tuning. In the older days of turbo-charging, we used to use manual boost controls that could alter/delay when the waste gate would open, thus giving greater boost level, and more power, before opening the waste gate/WG to vent according to the OEM prescribed boost peak. Yes, it was a very risky tweak, but those were the days before all of the modern ECU controlled systems. From my experience, reducing certain exhaust restrictions will have much effect on spool up and 'lag'. To reduce lag and gain more power down pipes were and are still very liked, as the increased exhaust flow allows the turbo to spool quicker, especially coupled with less restricted higher flow cats. Some guys removed the cats completely for best effect, but I'm not a fan or polluting with a daily driver. Modern systems use electronically controlled waste gates to control max boost pressure and to better control boost for given rpm, load, and gear. But, I'm still not getting why and how BMW is using waste gate activation to reduce lag at lower RPM, compared to stock. I can see controlling the WG over the rev range to better control and smooth out boost over the rev range and thus make power delivery more linear. And, of course the WG is used to limit max boost, as well as being utilized to get more max boost before it opens. As for lag off the line, to decrease any lag comparing stock to PPK, you're implying that the stock tune would actually be opening the WG as soon as the driver starts to give throttle. And the PPK is keeping the WG closed in the same scenario, in order to build boost quicker. BMW actually doing this would be contrary to building and tuning a turbo engine with near zero lag. Opening the WG even slightly right off idle would actually create lag and unnecessarily so. It doesn't make sense to tune the WG to open right off idle with either auto trans or manual, and would be even worse for MT as the clutch needs to be engaged in order to build adequate exhaust pressure to spin the turbo in the first place. Giving throttle while in neutral or with the clutch disengaged results in very little boost build. Your thoughts? Help me understand how BMW have altered the WG to reduce lag, especially on take off, right off idle. |
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05-02-2013, 01:34 AM | #31 | |
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The WG can also be computer controlled so that it opens and closes even before the max boost pressure is reached. This can be done to limit boost pressure within a certain rpm range, load, or gear, can can be used to smooth out power delivery. To release the pressurized air during a shift that's the job of a "blow off" valve. These come in two varieties. One is a "recirculating valve" and the other is "vented" valve. The"diverter valve" allows the pressurized air back into the intake stream. And if done properly will put that air right in the path of the compressor side of the turbo and can help lessen the effect of boost drop especially on fast shifts. A "vented" blow off valve opens to release the pressurized air to the atmosphere. Vented blow off valves make that cool "Phssst" sound. Diverter valves make virtually no sound. I love the sound of atmosphere vented blow off valves. Auto trans has the added benefit of holding boost during shifts as the trans is constantly coupled to the engine, and the driver doesn't have to lift/close throttle in between shifts as one does when driving a manual clutch trans. Dual clutch AT's can also hold boost, or not loose as much boost, in between shifts because the shift happens very quickly and the driver doesn't have to lift throttle in between shifts. |
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05-02-2013, 01:52 AM | #32 | |
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I can't say which is a bigger let down. I do know that with both combined BMW created a big let down for BMW "SPORT" sedan lovers. My 335i Msport was built in July and there have been at least 2 new revisions/different steering racks, and I read there is yet another one coming soon probably for the 2014 models. Some have said that the new racks have improved steering effort and feel. My 2013 335i isn't even a year old and it already has an outdated steering rack. This F30 sure is something new. BMW |
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05-02-2013, 07:33 AM | #33 | |
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05-02-2013, 08:24 AM | #34 | |
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05-02-2013, 10:43 AM | #35 | |
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My hypothesis is no based on: 1) MPPK would not retard timing at low RPM to increase exhaust pressure because this could hurt the engine, and honestly, why would you care about turbo lag at low RPM for a high performance tune? 2) The main increase in performance is in the higher RPM band, where the track driver would be anyways and the stock overboost protection is overly conservative - stock dyno runs show pretty dramatic torque drop above ~5.5k RPM. 3) You have the 8AT and probably experience a lot less lag. If there was one area I think BMW powertrain engineers really knocked it out of the park, it was tuning the ZF8. Edit - re-read and specifically curious why the waste gate would be open at idle and gradually close? You say this is for the N54, but I'm not sure why this would be the case with the N55...
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05-02-2013, 10:45 AM | #36 | |
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05-02-2013, 11:42 AM | #37 | |
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05-02-2013, 09:48 PM | #38 | |
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Steering feels exactly the same.
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05-02-2013, 10:27 PM | #39 | |
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05-02-2013, 10:30 PM | #40 |
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I think we need a poll. However, I don't think enough people have the MPPK yet.
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05-05-2013, 11:37 PM | #41 | |
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"Blow off" valve is the general term, "Recirc" and "atmosphere" describe where the pressurized air is being "blown off" to. |
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05-06-2013, 12:08 AM | #42 |
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Damn, where were you when I was getting ripped a new one in my thread?? LoL, oh well.
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05-06-2013, 07:58 AM | #43 | |
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Maybe it also depends on the packages on the 335i before mppk.
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