991 Over rev information

595triple · Dec 6, 2022

Decided to get my car back under a warranty and took it in for the mandatory 111 point check with my local OPC. It passed that all apart from showing over revs in RR3 and RR4. I was therefore told it had to have a compression check (£1050) before a new warranty would be considered.

As it was due an 8 year service I agreed upon ‘a price‘ to do it all at once as a lot of the compression test work is duplicated by the service.

At this point I asked to see the DME report. I had a sneaking suspicion that some over exuberance at Goodwood last year may have been the cause of the over revs. Looking at the DME, the engine time for the over rev basically confirmed that but oddly it showed I had 13 ignitions in RR3 but 20 in RR4. That should not be possible as you have to go through RR3 to get to 4! I question the OPC and they agreed (the fact they should have noticed this themselves seems to be lost). A support ticket was created with Porsche who confirmed it should not work that way and told the OPC to ignore the over rev data and allow warranty without the comp check. Result!

Out of interest I wanted to know what the over rev points were. There seems to be no info for the 991 anywhere online. The OPC obtained an info sheet (they did not know) and showed me. I was not allowed to have or make a copy of the sheet (??) but they did make a copy of the data for the Carrera which is

RR1 - 7800-7900
RR2 - 7900-8100
RR3 - 8100-8200
RR4 - 8200-8300
RR5 - 8300-8600
RR6 - 8600+

Normal max RPM is 7800, even though its marked as red from 7600 on my GTS tacho. RR1 and RR2 are ignored for extended warranty.

ralphmusic · Dec 6, 2022

I believe the rev count is measured by toothing on the flywheel, the number of teeth per revolution is counted via a Hall sensor, and interpolation between the tooth profiles.

In order to detect a speed difference at c7000 or more rpm, you need accurate interpolation across a reasonable number of teeth in order to get the required resolution. This can cause count errors if very small time windows are sampled and the speed is not constant over 360 degrees. In addition, there can be interference in the digital signal transmission. This measurement methodology is open to errors.

Rev Ranges 1 and 2 are normally ignored for warranty purposes, and yes you can "overrev” a PDK car. I was told by an OPC when I bought a PDK GT3 that it couldn’t be overrev’d. I insisted on a full ECU download and there were RR1, 2 and 3 revs reported, the latter were just 45 and I considered that to be anomalous, as did a second OPC when I later sold it on.

595triple · Dec 7, 2022

Interesting if you bought the GT3 from an OPC that it had RR3 info on it as that is an instant warranty fail. I assume they had seen that, done a compression test and then it was approved for warranty?

I asked the OPC that did the work for me what the future situation would be as the over revs cannot be cleared. They confirmed the support ticket with Porsches clearance was now on record for my car.

You have to really ask the question why, with an active effort to supply extended warranties, monitor rpms' and encourage track use (why else would you include a track use manual with the car), why they just don't fit a rev limiter to the engine like other companies.

ralphmusic · Dec 7, 2022

There is a rev limiter. Go over a sharp rise at full chat with high revs and the revs flair and can exceed the soft limiter.

I'm sure most car are like this, just that Porsche take a view for warranty.

As to my GT3, who knows if their warranty manager had noted the rev report, I at least was aware of overrev reporting.