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01-06-2013, 02:59 PM | #1 |
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recorded over-revs on stock engines?
I often come across in a variety of random threads the fact that several people and dealers have recorded some pretty insane overrevs from stock cars or even tuned cars with the regular 8400 redline. I am talking about DCt cars.
How is it that the car can record revs as high as 8900 in some cases with a DCt? I often drive mine right to redline and especially in 3rd often hit the fuel cuttoff just a bit and then I shift. If a car randomly overrevved even if you did nothing wrong and had no tune to increase limited, what would bmw do in that case? I thought the nannies in both DCt and manual prevented from overrevving within each gear (minus money shifting on a manual) |
01-06-2013, 03:05 PM | #2 | |
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Only mechanical over-revs are possible with a manual transmission..aka money shifting. |
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01-06-2013, 03:57 PM | #3 |
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My dealer recorded an over rev of exactly 12,000 rpm from the previous owner. Even the SA was skeptical about it. Cars is running fine after having one of its valve springs replaced.
EDIT: I should add a PUMA case was opened and BMW remotely accessed the ECU and saw the over rev, NOT the dealer.
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01-06-2013, 04:17 PM | #4 |
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Don't our cars have rev limiters though?
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01-06-2013, 06:00 PM | #5 |
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Guys that is my point. I am not asking about the theoretical chance, I am asking how it could happen given there are multiple documented accounts of revs that were 8600 plus on stock cars.
Mike Benvo I know has posted something on this or an example of some car in the past. Maybe he will chime |
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01-06-2013, 06:33 PM | #6 |
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Rev limiter will not save you from a mechanical over rev such as accidentally downshifting into 3rd instead of upshifting into 5th while at 8300 rpm in 4th. But this should occur only with 6 speed manual due to the computer controlling the shifts on the 7 speed DCT. Rev limit will save you from staying in the gear past the rpm limit or from free-revving beyond the limit, but it cannot defy the laws of physics from a mis-shift. A few people have done this on E36M3s with old, tired shift linkages and worn out tranny and engine mounts -- it is called the "money shift" because it is expensive to fix. But not as expensive as on a newer M3 for which the parts are much costlier.
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01-06-2013, 06:35 PM | #7 |
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DCT cars will hit almost 8,600 RPM in some cases in stock form.
6MT cars you can over-rev if you shift to the wrong gear. The highest one I've seen is 9,114 RPM and it's still running fine 20,000 miles later. Dealer can't see this information but BMW can.
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01-07-2013, 12:42 AM | #9 |
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This is what I mean-how often or when does the DCT hit 8600? Just randomly in a random car or if you redline the car constantly and you hit the limter a few times a week is this happening?
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01-07-2013, 01:20 AM | #10 | |
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Don't worry about it. Enjoy the car
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01-07-2013, 01:21 AM | #11 |
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The dealer doesn't have tools to be able to read freezeframe data. They use ISTA/P and ISTA/D exclusively (both of which I have), and they are 'dummed down' dealer systems and not expert tools.
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01-07-2013, 07:32 AM | #12 |
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Ok that makes sense. But what do you mean by "but BMW can"? Are you talking about BMW corporate? I dont get it.
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01-07-2013, 10:40 AM | #13 | |
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01-07-2013, 11:31 AM | #14 |
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Benvo during coding gave me the freeze frame info on my 6MT, had one mechanical overrev about 6 months prior to 8,800+rpm (likely due to wrong downshift)... 2 months later, differential nearly fell out of car due to bolt snap. BMWNA did come out and look at it, concluded that the diff bolt failure shouldn't have happened and approved the full diff and subframe replacement under warranty. Point is you're probably allowed a couple of "mulligans" with MT as long as it's not overly excessive (absolute amount and # of times), and with DCT probably a lot less to worry about.
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01-07-2013, 11:41 AM | #15 | |
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I wonder if there is preventative maintenance for this diff bolt issue. I'm going to get 295/30/19's because I think it will reduce wheel hop that I get with my 265/35/19's on an 11" wheel. I'm terrified of this happening to me. 47K on the clock now and so far so good (even with 500+ times to 8,800 RPM)... But then again I rarely launch the car.. Reminds me of the E46 subframe issues.. ridiculous to have fear to drive the car the way it's meant to be driven! I just love this car more than any other car I've had in my life and don't want to hurt it..
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01-07-2013, 12:00 PM | #16 | |
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Hi Mike, I did quite a bit of digging on this, it appears that using solid differential bolts (like GTS) would be a good preventative measure...they're available at some vendors (eg Turner Motorsports or maybe even the BMW dealers that sell Motorsport parts). What I was not able to conslusively ascertain was how it would affect NVH. If you find out about anyone who has done this and how it affected NVH, let me know, as once get out of warranty period, I would consider getting these installed.
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01-10-2013, 09:58 AM | #17 |
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I haven't had any issues at 30k miles. I am considering swapping out the bolts for new ones, just in case, but why mess with something and create a problem? Decisions...decisions.
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