Over-rev hit 16,000rpm "money shift" ...possible?? (1999 C4)
07-21-2009, 11:32 AM
#17
Race Director
Engine controller reports rpms in 1/4 rpm increments...
Hi All,
I recently had an engine die. Some of you may have commented on the related thread that is a general discussion about engine failure and my present options. However, the 16K RPM header may get a few people to chime in on this specific subject.
I was told by the first shop that the computer on the car said I hit 16,000rpm. ...thus the engine death was therefore the dreaded "money shift." (mis-shift)
Based on the situation, this implies that I was shifting from 2nd to 3rd - and mis-shifted into 1st at high RPM (6800). I do not think I made that shift - or any shift. I believe that I was in third gear before that track section.
Could such a mis-shift cause a 16,000RPM condition?
...even at red-line limiter engaged at about 7200 RPM
I'm sure there must be some money shift stories out there...
What gear were you in/planning to go to?
What happened to the car at that instant?
What damage was externally visible?
Did you get a report of how high the RPMs got?
...the rest of my story:
I am hearing a lot of conflicting information from shops regarding the potential cause of the blown engine. I called a couple other shops about a second/third opinions and they have told me that 16K RPM would not be possible and even if it "could happen," the heat would have caused molten metal, most likely a rod would have been thrown or other visible external damage and there should have been much more oil loss.
Note: when smoke came billowing out of the tailpipe, there was no "lurching" of the car, violent, loud noises, etc. There was also no oil dropped on the track - only out the tailpipe and minor seepage under the engine.
Have a great day!
I recently had an engine die. Some of you may have commented on the related thread that is a general discussion about engine failure and my present options. However, the 16K RPM header may get a few people to chime in on this specific subject.
I was told by the first shop that the computer on the car said I hit 16,000rpm. ...thus the engine death was therefore the dreaded "money shift." (mis-shift)
Based on the situation, this implies that I was shifting from 2nd to 3rd - and mis-shifted into 1st at high RPM (6800). I do not think I made that shift - or any shift. I believe that I was in third gear before that track section.
Could such a mis-shift cause a 16,000RPM condition?
...even at red-line limiter engaged at about 7200 RPM
I'm sure there must be some money shift stories out there...
What gear were you in/planning to go to?
What happened to the car at that instant?
What damage was externally visible?
Did you get a report of how high the RPMs got?
...the rest of my story:
I am hearing a lot of conflicting information from shops regarding the potential cause of the blown engine. I called a couple other shops about a second/third opinions and they have told me that 16K RPM would not be possible and even if it "could happen," the heat would have caused molten metal, most likely a rod would have been thrown or other visible external damage and there should have been much more oil loss.
Note: when smoke came billowing out of the tailpipe, there was no "lurching" of the car, violent, loud noises, etc. There was also no oil dropped on the track - only out the tailpipe and minor seepage under the engine.
Have a great day!
I have not seen inexplicable RPM spikes but I have seen inexplicable coolant temperature spikes from my 02 Boxster. Not very often, but the coolant temperature will come across with a translated value of 315F temperature. This of course impossible. The cause? I have no idea.
It is not therefore out of the realm of believability that the rpm sensor value could upon occasion be wrong and a wrong or invalid value recorded.
But to convince Porsche this occured and just so happened to occur on a track... Well, good luck.
Oh, read some time ago about a mag. writer blowing up a Carrera GT engine. Missed a shift and later analysis found engine hit 14K revs before letting go.
Sincerely,
Macster.
07-21-2009, 11:36 AM
#18
Race Car
07-21-2009, 12:39 PM
#20
Addict
Rennlist Member
Rennlist Member
Well those are "max possible" as he says, there's likely slip in the clutch and the tires before the engine is accelerated to it's final value, not to mention this presumes an instantaneous shift from exactly redline.
Anyway, I've seen too high an average speed reading too. My last M3 trip computer showed average speed of 198mph after a session on track, obviously not very likely.
I would like to add though, that an RMS/Clutch job can't really cause the type of failure you experienced, almost regardless of what they may have done wrong, and having worked at independent shops, I can also advise you that the last thing you want to do to this shop (if you like working with them), is to go there telling them how you read on the internet that their reading is wrong, and that they may be at fault. The reading is likely wrong, but due most likely to a bug in your engine computer -though I would also say that any competent engine builder should know that your engine didn't make it to 16k. However, a shop doesn't need to know this to be an effective and efficient independent garage to meet 99% of your needs.
Anyway, I've seen too high an average speed reading too. My last M3 trip computer showed average speed of 198mph after a session on track, obviously not very likely.
I would like to add though, that an RMS/Clutch job can't really cause the type of failure you experienced, almost regardless of what they may have done wrong, and having worked at independent shops, I can also advise you that the last thing you want to do to this shop (if you like working with them), is to go there telling them how you read on the internet that their reading is wrong, and that they may be at fault. The reading is likely wrong, but due most likely to a bug in your engine computer -though I would also say that any competent engine builder should know that your engine didn't make it to 16k. However, a shop doesn't need to know this to be an effective and efficient independent garage to meet 99% of your needs.
07-21-2009, 12:39 PM
#21
Burning Brakes
I was pretty sure from when I had PPIs done on cars I looked at that there were ranges of over revs, the numbers which I am sure can be found online, but something like 7300 to 7900 is Stage 1 overrev, 7900 to 8500 Stage 2, etc, with Stage 3 being Over 8500??, and the DME simply counts the number of sparks (as Jake Raby mentions above) in each Stage. I also thought it only logged engine run time at the last over rev spark, so if you looked at the current run time, it would tell you if the last over rev was the final death knell, or if it occured 120 hours of engine run time previous. The DME definitely does not record the overrev RPM.
07-21-2009, 12:55 PM
#22
Race Car
A V-8 would slip the clutch or tires - done it many times before without issue.
07-21-2009, 01:00 PM
#23
Three Wheelin'
out of curiosity I asked a friend, says 996 DME has only the two ranges:
Type 1: redline (hit the limiter)
Type 2: over redline (missed shift or raised rev limiter)
rev limiter redline and overrev counter redline are set independently
records total number in ignitions (6 per revolution)
does not record duration, only runtime of last occurrence
durametric will read it
Tell them to give you the actual data for the Type 2 count, and ask them how they determined you hit that rpm.
I do have to agree with Ahmet, I don't think anything at the clutch-job end would have caused death by valve float, but I would make sure it wasn't say IMS failure (I still think you'd have a hard time proving their fault if it was)
If it was valve float that killed your motor, I think you have a decent shot at rebuilding the top end and still having a good motor, but look at that block.
Type 1: redline (hit the limiter)
Type 2: over redline (missed shift or raised rev limiter)
rev limiter redline and overrev counter redline are set independently
records total number in ignitions (6 per revolution)
does not record duration, only runtime of last occurrence
durametric will read it
Tell them to give you the actual data for the Type 2 count, and ask them how they determined you hit that rpm.
I do have to agree with Ahmet, I don't think anything at the clutch-job end would have caused death by valve float, but I would make sure it wasn't say IMS failure (I still think you'd have a hard time proving their fault if it was)
If it was valve float that killed your motor, I think you have a decent shot at rebuilding the top end and still having a good motor, but look at that block.
07-21-2009, 04:05 PM
#24
Rennlist Member
you very well may not have mis shifted. Present them with challenging info about their lack of ability to pull a 16K rpm # out of the 996 DME, that info just isn't there, where did they get that?
2nd point. them doing a clutch job on the car and replacing the RMS (seal) would in no way ever have anything to do with your engine letting go however it did let go. I would abandon that line of thinking and focus on getting to the bottom of how your engine may be damaged and how best to fix it.
Sounds to me from everything you said that this shop in particular is not one that should underake diagnosing much less repairing your engine.. Period.
2nd point. them doing a clutch job on the car and replacing the RMS (seal) would in no way ever have anything to do with your engine letting go however it did let go. I would abandon that line of thinking and focus on getting to the bottom of how your engine may be damaged and how best to fix it.
Sounds to me from everything you said that this shop in particular is not one that should underake diagnosing much less repairing your engine.. Period.
07-21-2009, 04:35 PM
#25
Instructor
16k overrev is very possible! i know a guy who has a 20k aftermarket tach. http://www.samsmotor.se/koso/tacho.htm
and his money shift sent it to 15k
and his money shift sent it to 15k
07-21-2009, 05:03 PM
#26
Get them to send you the 16k number in writing. Maybe the best way to get them to do this would be in an email.
Keep every scrap of paperwork and document all interactions with them.
Show up unexpectedly and demand to see the engine, including the RMS, all seals, etc. Take pics.
If after doing all this you feel that they screwed something up, then take it to another shop for a second opinion.
In order to get them to take any responsibility for the engine failure, you will surely have to sue them. Get ready for a fight.
Keep every scrap of paperwork and document all interactions with them.
Show up unexpectedly and demand to see the engine, including the RMS, all seals, etc. Take pics.
If after doing all this you feel that they screwed something up, then take it to another shop for a second opinion.
In order to get them to take any responsibility for the engine failure, you will surely have to sue them. Get ready for a fight.
07-21-2009, 05:17 PM
#27
Race Car
16k overrev is very possible! i know a guy who has a 20k aftermarket tach. http://www.samsmotor.se/koso/tacho.htm
and his money shift sent it to 15k
and his money shift sent it to 15k
07-21-2009, 06:16 PM
#28
16k overrev is very possible! i know a guy who has a 20k aftermarket tach. http://www.samsmotor.se/koso/tacho.htm
and his money shift sent it to 15k
and his money shift sent it to 15k
07-21-2009, 07:19 PM
#30
Addict
Rennlist Member
Rennlist Member
If my old gear charts are right you would need to be spinning your rear wheels at 89 mph in 1st gear to hit 16k. I'd be pretty surprised if you could get the car into 1st at that speed and if you did you'd know it. It's highly unlikely you'd keep the car on the track. At a minimum you would feel the rears lock up and hear the engine screaming for mercy.