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Here's mine. 1999C2 3.4L rebuilt as 3.8L.
The dyno chart title says 4.0 but it really is 3.8L
The before in this case was done after the build to 3.8L and the after is with the dyno tune which better matched the various changes to work together.
Here's mine. 1999C2 3.4L rebuilt as 3.8L.
The dyno chart title says 4.0 but it really is 3.8L
The before in this case was done after the build to 3.8L and the after is with the dyno tune which better matched the various changes to work together.
What a crazy drop in tq/hp at 6krpm.......... looks like knock control kicking in (retarding timing ?) from the Wevo SS mounts ?? Looks like the tuner was able to "fix" it and then some...
I wondered the same thing at the time based on some comments and video from Jake R so i went back to factory OEM mounts earlier this summer just to be sure.
I wondered the same thing at the time based on some comments and video from Jake R so i went back to factory OEM mounts earlier this summer just to be sure.
Yep, looks like the 2nd order vibrations/knock retard started at 5700 RPM and the tuner saw that and tuned it out...
I bet by going back to the stock mounts you picked up some power at 2850 RPM also.... according to the graph looks like the 1st order vibration/knock retard starts at 2850 RPM and was not tuned out by the Tuner, but going back to stock mounts probably cured this dip also...
A 3rd order vibration would have shown up at 10,400 RPM , lol...... had the engine been reved this far..I have dealt with 3rd order vibrations back in the day , they are WICKED....lol
Last edited by Porschetech3; 09-27-2022 at 04:07 PM.
Here's mine. 1999C2 3.4L rebuilt as 3.8L.
The dyno chart title says 4.0 but it really is 3.8L
The before in this case was done after the build to 3.8L and the after is with the dyno tune which better matched the various changes to work together.
Thanks for sharing ! And yeah, the dips are interesting. What peaks my interest on the 2nd one, if it was knock control, I would expect to see the AFR go rich - in your case, it goes lean. Having the AFR go lean in an engine stress event like the introduction of knock control timing retardation is not what I would think the best scenario. I don't know anything about the factory knock control strategy so just my observation, that behavior may be totally normal for all I know.
Glad the tuner was able to work it out - looks like on your setup the tune was an absolute must to take advantage of the rest of the combination.
AFR numbers from 02 Sensors are not always what they seem..
02 sensors read Oxygen only and are not infallible...
After combustion the 02 Sensor reads Oxygen content only..
If a spark event is missing ( missfire) there will be extra Oxygen AND fuel in the exhaust , but the 02 Sensor will only notice the Oxygen..therefore show lean when in reality the AFR was correct going IN to the cylinder..
Same thing happens to a lesser extent when timing is retarded, timing is retarded to control knock by lessening the combustion pressures, by not having "complete combustion" ' of the A/F mixture . The incomplete combustion from retarded ignition timing causes extra Oxygen AND fuel to be in the exhaust but the 02 sensor only reads the Oxygen and therefore reads lean when infact the correct A/F may have been going IN to the cylinder...
Same thing happens to a lesser extent when timing is retarded, timing is retarded to control knock by lessening the combustion pressures, by not having "complete combustion" ' of the A/F mixture . The incomplete combustion from retarded ignition timing causes extra Oxygen AND fuel to be in the exhaust but the 02 sensor only reads the Oxygen and therefore reads lean when infact the correct A/F may have been going IN to the cylinder...
Are you sure the above is accurate ?
We’re talking about a knock control strategy where ignition timing is retarded, not advanced. How are you retarding the ignition event to such an extent that you are not seeing full combustion ? The AFR is set when the intake valve closes, retarding the ignition event gives MORE time for a full combustion event, although at a far lower cylinder pressure. It is the lower combustion pressure that reduces knock, not incomplete combustion, I think that would be referred to as a misfire.
I don’t see how there is an affect on AFR in this scenario. Maybe you can explain, I would like to know where my thinking is off.
We’re talking about a knock control strategy where ignition timing is retarded, not advanced. How are you retarding the ignition event to such an extent that you are not seeing full combustion ? The AFR is set when the intake valve closes, retarding the ignition event gives MORE time for a full combustion event, although at a far lower cylinder pressure. It is the lower combustion pressure that reduces knock, not incomplete combustion, I think that would be referred to as a misfire.
I don’t see how there is an affect on AFR in this scenario. Maybe you can explain, I would like to know where my thinking is off.
Remember, this is not an "actual knock", this is a vibration that is "incorrectly interpreted as a knock"....
The ignition timing didn't actually "need" to be retarded, as shown by the after tune graph..
Retarding the timing an unnecessary amount causes incomplete combustion..
This is a 5 chain engine. Couldn't the dips be the Variocam disengaging after ~5500 RPM? And then the RSP tech tuned it to stay engaged, if this is possible? The graph begins after 1500 so can't see the effect down low, not that it matters.
This is a 5 chain engine. Couldn't the dips be the Variocam disengaging after ~5500 RPM? And then the RSP tech tuned it to stay engaged, if this is possible? The graph begins after 1500 so can't see the effect down low, not that it matters.
You're just dreaming up stuff, no, it couldn't...lol...The vario-cam on a 5 chain is either OFF or ON , it switches at 1200rpm and then again 5120rpm...
You're just dreaming up stuff, no, it couldn't...lol...The vario-cam on a 5 chain is either OFF or ON , it switches at 1200rpm and then again 5120rpm...
A little bit of a harsh response to my question, but ok, I guess that happens once in a while from some here on RL Of course it is either On/Off, but it does this off at approximately at 5500 RPM. This is pretty consistant with the actuator loosing oil pressure after turning off and the dyno chart.
Source:
A little bit of a harsh response to my question, but ok, I guess that happens once in a while from some here on RL Of course it is either On/Off, but it does this off at approximately at 5500 RPM. This is pretty consistant with the actuator loosing oil pressure after turning off and the dyno chart.
Source:
I was wondering where you got the 5500rpm from...the actual rpm for 986.1 and 996.1 is 1200rpm and 5120rpm and is a long way from the graph which "starts at about 5700rpm and carries through 6000rpm...and without a reasonable explanation as to "why" there would be a lose of vario-cam function, it is a very far fetched idea..ie not plausible....
09-27-2022, 10:56 AM
Of course it is either On/Off, but it does this off at approximately at 5500 RPM. This is pretty consistant with the actuator loosing oil pressure after turning off and the dyno chart.
