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So my Cobb Accessport has opened a world of data to my fingertips. It's almost worth the price of entry for that alone. Yet it doubles and triples as an incredible flash manager and logger.
That said, I'm interested in what's considered normal noise registering in the knock sensors and potential sources. At light to medium-light throttle, I often register some knock voltage. Around the 2.5k to 3k rpm range. This is not full on throttle type knock we're discussing, which is obviously bad. It's an academic discussion as there's no real consequence.
Some of this noise seems to be from shifts/clutch as I will get sporadic readings with shifts. I'm on SRE 764 clutch with solid disk, not too dissimilar to stock.
Does variocam system make noises that can register?
Under light throttle, is the metzger motor known to make some piston slap/rattle, especially at lower rpm?
There was some suggestions that it's possible for semi's or solid engine mounts to add noise as well? Though I'm on my stock mounts.
Sub'd, as my new-to-me TT threw misfire codes this week, at light load in 2nd gear. My sense is yes, the engine must have some natural harmonics that sound like pings to the knock sensor, but that's a WAG. Also on stock, likely worn, mounts.
...what's considered normal noise registering in the knock sensors and potential sources. At light to medium-light throttle, I often register some knock voltage. Around the 2.5k to 3k rpm range. This is not full on throttle type knock we're discussing, which is obviously bad. It's an academic discussion as there's no real consequence.
Some of this noise seems to be from shifts/clutch as I will get sporadic readings with shifts. I'm on SRE 764 clutch with solid disk, not too dissimilar to stock.
Does variocam system make noises that can register?
Under light throttle, is the metzger motor known to make some piston slap/rattle, especially at lower rpm?
There was some suggestions that it's possible for semi's or solid engine mounts to add noise as well? Though I'm on my stock mounts.
While the throttle may be "light" to "medium" cylinder filling may be quite good and the combustion pressure obtained could generate some knock (detonation) signal. My info is Porsche runs its engines at close to incipient detonation.
Detonation at any engine speed is bad. While it might take a bit longer exposure to detonation at slower engine speeds to ruin the engine it will be ruined just the same as if the detonation happens at higher engine speeds.
One can observe driving the car with light to medium throttle how the ignition timing often is quite advanced. When I did this with my 2006 GTO not only would the timing get quite advanced, but the instantaneous fuel mileage reading would go almost sky high up in the 35mpg range. The GTO engine was a 6.0 OHV V8 with no fancy variable valve lift/timing control too. That extreme advance under the right conditions helps the engine become quiet efficient. This explains why Porsche uses high compression and runs the timing advanced as much as it can be (safely) to maximize the efficiency of its engines.
Compare this to say under heavy throttle when the timing is retarded some. It doesn't have to be due to detonation. Under heavy throttle the DME will enter open loop mode and ignore the #2 O2 sensor readings while it richens the mixture to help meet the torque demand of the driver. The richer mixture burns quicker and thus doesn't need as much advance to have it burning at the optimum time in the piston's power stroke.
By "does the VarioCam system make noise" are you referring to sounds or electrical signal noise?
The variable lift only comes into play at low RPM, like at cold start, or at low RPM operation. The noise one hears at cold start is mainly the sounds of the engine as it burns a rich mixture on purpose. The intent is to supply too much fuel and the excess will burn in the converters to warm them up quicker. That is why the secondary air injection system is running. At this time if the car is in a relatively quiet place one can hear the backfires in the exhaust. Typically of a rich running engine. As soon as the converters/sensors are hot enough though the rich mixture is cut back and the engine RPMs drop and the engine gets pretty smooth, for a Turbo engine.
At the same time, during cold start, the low intake valve lift is active. This low intake valve lift reduces pumping losses and reduces valve train parasitic loss which improves fuel consumption, and lowers emissions. (A form of "gaming" of the emission/fuel economy tests.)
The variable valve timing comes into play at other times, at higher RPMs, but I don't recall the RPMs. It may be quite variable -- no pun -- that is depending upon engine RPMs, load, torque demand, etc. The older VarioCam system without the variable valve lift and with an either advanced or not advanced control of the intake cams had pretty fixed RPM points at which timing was advanced or brought back to the standard timing.
If the Cobb system has the ability you can monitor cam timing adjustment maybe and see when and by how much it changes.
Piston slap is possible but you'd notice it at idle I think. Oil consumption would be high, as well. What you are probably hearing is the crankshaft to layshaft gear drive. It can make some racket at low engine speeds. I do not know what if any attenuation of this noise the non-stock clutch system could be responsible for.
Or the noise could be something rattling in the exhaust, a heat shield loose, etc.
A lot of time at quick throttle changes the car will register small quick cylinder knock which is what this may be recording. It is very common in Porsche's.
Shoot me over a log I would be happy to look into it more in depth.
