I am trying to buy my first 911 - 06 C4S with just under 40k miles. Based on the to a person feedback from the forum I had the DME report run. Here's what came back. How should I interpret (assuming all else with car looks good)?

NMax_1 640 1083.2 h
NMax_2 127 1083.2 h
NMax_3 004 1083.2 h
NMax_4 000 0.000 h
NMax_5 000 0.000 h
NMax_6 000 0.000 h

Thanks for the help!

 

I think I left off a number that matters.

Operating hours counter = 1107.000

 

It looks OK - someone hit the rev limiter 24 engine hours ago or about 900 miles ago. Get a copy of this month's Excellence magazine and read the article on over-revs.

 

Thanks, jhbrennan. I'll pick up a copy of the magazine.

 

I don't know if it ok with the OP but it is obviously the previous owner did a lot of racing. What it telling you is the previous owner consistently revving the RPM to 7500 at 640 times, 7700 rpm at 127 times. Obviously the previous owner did some sort of tracks or racing on the highway a lot. Well, the question is would you want to buy a car that someone did pushing that hard on the engine

 

Thanks, Gotgolf52. Does the DME show the number of times into the rev range, or the cummulative number of ignitions in the rev range? Huge difference in interpretation of the report I got depending on the answer. Thanks!

 

I'm sure it is the number of ignitions and that report is fine. Do a search to get better information. The Excellence article will make you worry less about 1/2 over revs. Comes with the territory unless you buy a garage queen and then you have other worries. Good luck

 

Not entirely accurate. This is a really good DME report. The counter shows the number of spark plug ignitions while at RPMS near and above redline. 640 ignitions is nothing, no worries here. It's not the number of times it hit redline.

A tracked car will show 100X more ignitions in range 1 (60,000 or more).

 

Snee

Deciphering the DME report goes like this:

Each range, 1-6 corresponds to an RPM range. Don't know exactly what the 997 numbers are, but generally range 1-3 over revs are "acceptable", 4 and above are a relative concern.
Here is what the numbers mean.

The engine DME records cylinder ignitions (sparks) when they occur within the ranges 1-6. Below ranges 1-6 are lower rpm.
With an engine operating at ~3000 rpm there are ~50 revs/sec, with 6 cylinders makes it ~300 sparks/sec.
With an engine operating at ~6000 rpm there are ~100 revs/sec, with 6 cylinders makes it ~600 sparks/sec.

Each count (640) in range 1 indicated the engine spark occurred above the specified rpm - maybe in the 7000-7200 rpm range for range 1. So let's say a missed down shift occurred and it lasted ~1 sec, it would record ~699 range counts (7000/60=116, x6=699). If it was a fraction of a sec., let's say 1/10th, it would be ~69 counts.

1083 hours on all the ranges indicates the sparks were recorded at the same moment.

Same logic applies for the higher ranges.

I'd say your OK with the numbers indicated.

Bob D

 

It's obvious from some of the responses here that the concept of over-rev ignitions is not understood. The DME report shows the number of ignitions recorded in a specific rpm band. It's a cumulative amount so you don't know if the over-revs happened at the same time or over a period of time. What this report does tell us is that there have been 640 ignitions in range 1, the last one occurring at hour 1083.2. If I did my math right and using 7200 rpm as range 1 (not sure what it is for OP's engine) 7200 rpm = 120 rev/second and with 3 ignitions occurring every revolution, 640 ignitions is the equivalent of less than 2 seconds of a range 1 over-rev condition. As I said previously, I think that's OK...but I'm not the buyer so he'll have to make his own educated decision.

 

We may be saying the same thing but what the 1083.2 recording says is that the last over-rev condition was recorded at this engine hour - it could have been all 640 ignitions then or a lesser amount, we just don't know. So this report would indicate that an aggressive drive occurred at this hour since the engine hit the rev limiter for ranges 1 and 2 with a slight incursion into range 3 all at the same hour.

 

This is a good DME article to read up on - https://www.6speedonline.com/forums/...tive-post.html

 

Thanks all for the great input. Super helpful. Keep it coming. I believe the consensus is this DME report is acceptable? I worry a bit the last over rev happened relatively recently and likely was the first incursion into range 3 (probable damage zone?). Am I over thinking this? First time buyer; so, no experience with knowing what these engines should be able to withstand without impact to their longevity. I want to buy and keep for a long time.

 

Looks like someone made one bad shift a little while ago. Possible wheel on a test drive? I wild not be discouraged from that report. That report is not indicative of someone doing allot of racing. In fact, it looks like it was babied aside from one incident. The only concern would be its recent occurrence. If something was damaged, it might not have had time to reveil itself.

 

Actually level 1 and 2 overrevs are not usually the result of a bad shift. They are registered when you hit the rev limiter and are of no consequence. OP needs to be careful, not because of the report, but because of misinformation on this thread. The report should not be the determining factor in your purchase. It seems fine. Checking for service records, esp oil changes and for accident damage is more important.