Thoughts on this DME report?
Racer
Joined: Jun 2011
Posts: 484
Likes: 3
From: NorCal
Can you say "stretched connecting rods"?
Seriously, it looks like a down shift or bad data from about 18,000 miles back. 51 ignitions is 17 crank rotations which is a fraction of a second in ranges 4 and 5. Conventional thinking is that damage from overrevs shows up shortly after the event. 18,000 miles should be plenty to reveal an overrev induced problem.
Some naughty driver spent some time at or just above the redline about 2,000 miles ago. I think Dr. Porsche would approve
Seriously, it looks like a down shift or bad data from about 18,000 miles back. 51 ignitions is 17 crank rotations which is a fraction of a second in ranges 4 and 5. Conventional thinking is that damage from overrevs shows up shortly after the event. 18,000 miles should be plenty to reveal an overrev induced problem.
Some naughty driver spent some time at or just above the redline about 2,000 miles ago. I think Dr. Porsche would approve
Last edited by j beede; Mar 19, 2018 at 10:06 AM.
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From: Clemson, SC
That car had been driven pretty hard regularly from the more recent range 1s, 2s, and 3s, and numbers of them, possibly at some track days, not that there's anything necessarily wrong with that. Would I personally buy that particular car, no, probably not with so many to choose from.
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Joined: Jun 2001
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From: San Antonio
No, I'm 99% sure Dr. Porsche would want fans of his cars to wring their hands endlessly about whether they may have been driven enthusiastically a few times, and would advise you only buy ones used to pootle to the grocery store twice a week. 
Instructor
Joined: Jul 2016
Posts: 190
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From: Pasadena, CA
No, but in my limited experience seeing these things, the picky individuals I associate with tend to shy away from the potential to have problems. So they simply don't purchase cars with recent (recent is a relative term) high-range overrevs.
200 hours is the 'accepted' danger zone. This is a guideline that many people use:
http://www.911virgin.com/porsche/rev-range-information/
200 hours is the 'accepted' danger zone. This is a guideline that many people use:
http://www.911virgin.com/porsche/rev-range-information/
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Racer
Joined: Jun 2011
Posts: 484
Likes: 3
From: NorCal
A total of 51 range 4 + 5 ignitions = 17 crank rotations. At ~7900 RPM that's about an eighth of a second. If any valve hit any piston or a cam chain stretched I think 500 hours would be more than enough time for that damage to show itself.
Range 5 is wider than ranges 1/2/3/4. A range 5 overrev could mean 8400 RPM or it could mean 9500--assuming 911virgin's chart is correct. In any case, two range 5 ignitions seems to be an unusual number to be stored. That's less than one crankshaft revolution. How could you spin the crank up to 9000 or 9500 RPM and get it back down below 8400 again before completing one complete revolution? Something is odd here. My guess is that this is bad data stored or the excursion into range 5 was shallow and brief for the 997 being considered.
Range 5 is wider than ranges 1/2/3/4. A range 5 overrev could mean 8400 RPM or it could mean 9500--assuming 911virgin's chart is correct. In any case, two range 5 ignitions seems to be an unusual number to be stored. That's less than one crankshaft revolution. How could you spin the crank up to 9000 or 9500 RPM and get it back down below 8400 again before completing one complete revolution? Something is odd here. My guess is that this is bad data stored or the excursion into range 5 was shallow and brief for the 997 being considered.
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I like to think about this data in familiar terms so you can get a real world feel for how the car was driven. The exact time spent in each rev range is dependent on the actual RPM it was recorded at, but if you average everything to 7200 RPM than 1 second = 360 ignitions. So in the first 1558 hours of operation the subject car spent:
Rev range 1 = 33 seconds
Rev range 2 = 4 seconds
Rev range 3 = 1/2 second
Rev range 4 = 1/8th second
Rev range 5 = less than 1 revolution
Range 1 and 2 are pre-limiter, but the duration of time spent there was not accumulated from missed shifts, its from spirited driving. And though 37 seconds seems like a long time when thought of as happening in a single instance, when put in the context of about 1/2 second per thousand miles driven it seems more reasonable. I would think the 3,4,5 hits may be a single missed downshift, and to me (in this case) are less indicative of the cars use than the range 1,2 records. Another piece of info you can get from this is dividing the total miles by the total time, which in this case gives you an average speed of 39 mph over the life of the car. I hope this helps with your decision.
Rev range 1 = 33 seconds
Rev range 2 = 4 seconds
Rev range 3 = 1/2 second
Rev range 4 = 1/8th second
Rev range 5 = less than 1 revolution
Range 1 and 2 are pre-limiter, but the duration of time spent there was not accumulated from missed shifts, its from spirited driving. And though 37 seconds seems like a long time when thought of as happening in a single instance, when put in the context of about 1/2 second per thousand miles driven it seems more reasonable. I would think the 3,4,5 hits may be a single missed downshift, and to me (in this case) are less indicative of the cars use than the range 1,2 records. Another piece of info you can get from this is dividing the total miles by the total time, which in this case gives you an average speed of 39 mph over the life of the car. I hope this helps with your decision.