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2008 Cayman Rev Report

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Old 10-29-2015, 10:58 PM   #1
Johnson97471
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Default 2008 Cayman Rev Report

Hey Guys, I'm brand new here and working on a deal for a 2008 Cayman S with a 6spd. I had the PPI done today and would like to get your opinion before I continue the purchase. I've been reading as much as I can but it seems like alot of different opinions when it comes to the rev report. I understand a person doesn't want to see anything in the 4-6 range if possible correct? Is the range 6 number possible without seeing it in the other 5 ranges?

RANGE 1 - 5766 - 641.8 HOURS
RANGE 2 - 204 - 641.8 HOURS
RANGE 3 - 16 - 641.8 HOURS
RANGE 4 - 4 - 222.7 HOURS
RANGE 5 - 4 - 222.7 HOURS
RANGE 6 - 3 - .4 HOURS

Thank you in advance, Craig
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Old 10-30-2015, 05:12 PM   #2
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Hey again, I didn't get any responses on this one so I'm going to pass on the car. I had a full PPI done and would definitely encourage others to do the same. Well worth the money.

Thanks, Craig
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Old 10-31-2015, 12:50 AM   #3
Spokayman
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Craig,
I will qualify that I am not any sort of expert on overrevs on Porsche M97 engines, but I have read many times that level 4-6 are the dangerous revs.
However the duration of revs in each level (number of engine revolutions) and when the overrev incidents happened are the most important factors.
For example if the overrevs occurred at 222 hours and the engine currently has 700 hours and there is no sign of rod knock, oil consumption, or valve damage, then I would be far less concerned than if the overrevs occurred at 650 hours.
I'm sure those that DE, autocross, or even race their Caymans could give a more reassuring answer as to just how "bad" overrevs are.
I suspect the car you were looking at was just fine as far as overrevs were concerned though.
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Old 11-01-2015, 10:54 AM   #4
Frank 993 C4S
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Quote:
Originally Posted by Johnson97471 View Post
Hey again, I didn't get any responses on this one so I'm going to pass on the car. I had a full PPI done and would definitely encourage others to do the same. Well worth the money.

Thanks, Craig
Good move!

Here is a good explanation of the over revs:
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Old 11-02-2015, 01:01 AM   #5
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Looks like it had a missed shift on a test drive or first drive...

It did one revolution at stage 6, 1 1/3 revolutions at stage 5 and 1 1/3 revolutions at stage 4 and 5 1/3 revolutions at stage 3. The three stage 6, three of the stage 5, three of the stage 4 and three of the stage 3, three of the stage 2 and 3 of stage 1 all occurred on the same event, likely a missed shift. It had another missed shift at some point as well were it picked up another 1/3 revolution at stage 4/5.
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Old 03-18-2017, 02:20 PM   #6
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Default Over Revs or Ignition Events

A friend was looking at an '06 Boxster recently so I did some searching for over revs for him (among other things; e.g., water pump, rear main seal, clutch cables, etc.) before he has a PPI done and came across this post. I also looked through my old "Excellence" magazines for an article I remembered and found it in issue #215, December 2013. I put "stick-ums" on the magazine covers when I see something of interest so I can find it again fairly easily. According to the author of the article, "Porsche is more likely to forgive certain over-rev events if the motor in question has accumulated at least 200 hours since the occurrence, the thinking being that if the motor has been okay for that amount of time, then no damage was done." His words not mine. I certainly wouldn't pass on an awesome deal if there were one or two occurrences of short durations in 5 or 6 AND it met the >200 hours criteria the author noted and Spokayman eluded to. Great bargaining tool if noted during the PPI and the seller hasn't read this article. I'm sure there are a lot of other opinions on this subject.

Last edited by ottobon100; 03-19-2017 at 10:47 AM.
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Old 03-22-2017, 06:17 PM   #7
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Hmm, judging from the chart, perhaps I should stop using the rev limiter as a handy upshift indicator.
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Old 03-25-2017, 10:08 AM   #8
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It would be virtually impossible to get past a Range 1 overrev during an upshift. Range 2 and above is really only possible during a downshift.
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Old 03-25-2017, 10:14 AM   #9
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It would be virtually impossible to get past a Range 1 overrev during an upshift. Range 2 and above is really only possible during a downshift.
You can get range #2's with hard bangs of the limiter, and Sport Chrono (since SC gives you a harder red-line). Also, with an extreme spin, since the engine is not protected if spun backwards, but this is rare.
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Old 03-25-2017, 10:40 AM   #10
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The engine would exceed redline turning backward?
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Old 03-25-2017, 10:44 AM   #11
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The engine would exceed redline turning backward?
Yup. Very rare. Can happen. That's why you hear, "clutch in" on a severe track spin.
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Old 03-25-2017, 01:02 PM   #12
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When I bought my Cayman I had it inspected at Lufteknic in Richmond. I cannot remember the exact number of overrevs but I had something like 3 in zone 3 and 1 in zone 4. The issue, as the tech explained it, is the sample rate of the computer. It cannot pick one ignition cycle out at 8,000 rpm - which would take 25/10,000 of a second. So, he said there is a known issue that if you bang off the rev limiter the computer will extrapolate and just put cycles in the upper zones. It made sense to me and I bought the car.
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Old 03-27-2017, 12:07 PM   #13
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When I bought my Cayman I had it inspected at Lufteknic in Richmond. I cannot remember the exact number of overrevs but I had something like 3 in zone 3 and 1 in zone 4. The issue, as the tech explained it, is the sample rate of the computer. It cannot pick one ignition cycle out at 8,000 rpm - which would take 25/10,000 of a second. So, he said there is a known issue that if you bang off the rev limiter the computer will extrapolate and just put cycles in the upper zones. It made sense to me and I bought the car.
8000 RPMs is 133.3 revs / second. That's one rev every 0.0075 seconds. 3 ignitions per rev is one ignition every 0.0025 seconds, which is 25/10,000.

A DME miroprocessor running at 16MHz executes one instruction every 1/16,000,000 of a second. At that clock speed the processor can execute 40,000 instructions in that 0.0025 second time frame. The microprocessor has plenty of time to pick one ignition cycle out.

(Automotive DME's probably run at higher clock speeds than 16MHz. An automotive test tool I worked on ran its microprocessor at 20MHz. A railroad track and train controller system I worked on ran its 2 microprocesors at 20MHz (and a 3rd at 16MHz). Automotive DMEs can even run faster to 32Mhz or even 48MHz, or possibly even faster.)

Also, once the engine speed is above "redline" the DME no longer has to calculate fueling so its processing path becomes shorter, involves fewer instructions. Since the factory relies upon the DME over rev counter contents to allow or deny warranty repairs there is every reason for these counts to be very accurate. In one case Porsche doesn't want to hand out new engines under warranty if the DME failed to recognize a serious over rev. OTOH, Porsche doesn't want to deny a legitimate warranty claim based on spurious over revs counts. This in case someone challenges a warranty denial based on overrev counts.
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Old 03-27-2017, 05:28 PM   #14
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Quote:
Originally Posted by Macster View Post
8000 RPMs is 133.3 revs / second. That's one rev every 0.0075 seconds. 3 ignitions per rev is one ignition every 0.0025 seconds, which is 25/10,000.

A DME miroprocessor running at 16MHz executes one instruction every 1/16,000,000 of a second. At that clock speed the processor can execute 40,000 instructions in that 0.0025 second time frame. The microprocessor has plenty of time to pick one ignition cycle out.

(Automotive DME's probably run at higher clock speeds than 16MHz. An automotive test tool I worked on ran its microprocessor at 20MHz. A railroad track and train controller system I worked on ran its 2 microprocesors at 20MHz (and a 3rd at 16MHz). Automotive DMEs can even run faster to 32Mhz or even 48MHz, or possibly even faster.)

Also, once the engine speed is above "redline" the DME no longer has to calculate fueling so its processing path becomes shorter, involves fewer instructions. Since the factory relies upon the DME over rev counter contents to allow or deny warranty repairs there is every reason for these counts to be very accurate. In one case Porsche doesn't want to hand out new engines under warranty if the DME failed to recognize a serious over rev. OTOH, Porsche doesn't want to deny a legitimate warranty claim based on spurious over revs counts. This in case someone challenges a warranty denial based on overrev counts.
First, thanks for verifying my calculation of 25/10,000's is correct - I am an engineer and my abacus is in for repairs .

Second, I don't dispute your math on the processor as long as we agree it is not just sampling the ignition cycle. Also, is your claim that once the processor no longer is calculating fuel those lanes switch to the ignition cycle? I am not saying it is not possible it just seems unlikely Porsche programmed that in.

I do not know anything about Porsche warranty claims based on DME overrevs nor what factors, if any, beyond looking at the log they may take into account. Absolutely no knowledge whatsoever. I do find it interesting that a previous post stated that if 200 hours had elapsed after an overrev condition, that Porsche may wave that occurrence as damaging the motor. It seems to me that if their DME was infallible there would never be a reason to discount an occurrence and stick strictly by the chart.

That said, I based most of my purchase on the PPI I had done and the conversation I had with the Certified Porsche Technician that performed the PPI. If asked, I recommend PPI's by qualified personnel and discussing the results of the PPI with said person. Discussing results with someone who works on these cars regularly and sees far more issues than most of us is invaluable in my opinion.
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