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Plex V2 Questions

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Hi Andre/fellow tuners,

I have the plex knock monitor V2 system and I have a couple question I am hoping you or someone familiar with it can shed some light on.

Firstly, let me explain a bit how I have mine set up. I have an inductive clamp wired into the plex harness in order to easily pick up a trigger signal on different engines. As such I am able to utilize the variable noise threshold with changing rpm feature.

My first question is with regard to the sound of knock. I have done quite a few of the HPA courses and also looked at many webinars where you played sound data so we can hear what knock sounds like through the headphones. I believe I have the hang of this, but with my plex, using the 10k filter I seem to be hearing a very distinct difference vs the background noise........it is however not like the what I have heard from the HPA material. It almost sounds like plex are making it dummy proof and have highlighted the knock with a completely different tone.....not like what I have heard on the course material where you really need to listen to identify knock. I am wondering if this is a feature on the V2 that plex have employed to make things easier or if what I am hearing is infact not knock at all!

I have set up the variable noise threshold and I do hear the noise and see the light flash on the plex when it crosses the threshold at the same time. Some clarification on this would be appreciated.

My second question builds on the first. Is the variable threshold you set on the plex device it self and the audio you hear through the head set independent of each other? In other words, is what I am hearing on the headset what the engine is really doing? Or is the threshold I set up basically giving me an indication as well through the head set when the knock threshold is crossed and hence I am hearing this artificial sort of noise when knock is encountered through the headset? I am not sure if you understand what I am saying.

I was under the impression that the audio is completely independent and would always allow me to hear exactly what the raw engine is doing regardless what settings I change on the device (filter frequency aside of course).

I am on a shitty emanage ultimate so it is making tuning changes very unpredictable so I cannot be sure that the engine is actually receiving less ignition timing when I tell it to do so through the emanage, and I have no way of logging the stock ecu to confirm hence adding to my confusion in the midst of all of this.

Bump for this, still waiting on any insight from anyone thats familiar with the plex.

Sorry for the slow reply. You're right, the sound that you hear from the Plex with the 10 kHz high pass filter is very different to the background engine noise. This is something I believe Plex have purposely done to distinguish the noise and make knock very clear, which for the most part it does exceptionally well. As I've posted in other threads, you can't apply the 10 kHz filter to every engine though as you may end up triggering the knock audio when in fact the engine isn't knocking. If you use the unfiltered setting then this will sound more like what you'd expect from the examples in our webinars and course material.

The noise threshold and the audio are independent of each other. The noise threshold needs to be tuned under 'no knock' conditions and can be confirmed using the audio output to ensure the engine wasn't knocking. When you have the threshold tuned correctly then the plex will indicate knock visually at the same time you hear it.

If you're tuning on an emanage I would be wary of your results. As you've indicated already, these units seem to use the 'spray and pray' method when it comes to fuel and ignition timing and your results may vary dramatically from one run to the next. I straight out refuse to tune them :(

Hi Andre,

Thanks for the reply.

So tell me this, if you have configured the variable noise threshold under safe ignition settings, is it advisable to simply rely on the lights on the unit flashing and forgetting about the audio?

Also, when you configure the noise threshold, we are doing so under WOT condition ramp run. Can I rely on the lights on the unit for detecting knock while steady state tuning at part throttle as well?



I generally use the audio always, but that's probably from using other systems without visual warning. If the lights are accurately detecting knock then I see no reason why you can't rely on them. It all comes down to correctly configuring the threshold to start with.

The noise threshold needs to be configured under WOT conditions during a ramp run. You want the ignition timing pretty close to optimal though, so don't think you can pull 10 degrees out to be 10% sure the engine isn't knocking and then use that as your threshold. As you get closer to MBT, the engine's background noise level tends to increase a little.

Thanks for the reply Andre,

Understood on simply not overly retarding the ignition timing to begin with.

As for the second part of the question, my question really surrounded on if using the threshold that we established under WOT will still hold accurate when we tune in steady state and correspondingly the engine background noise level would now be different to what we configured the threshold on earlier at WOT. So is it now a case of the tuner audibly detecting what is real knock under part throttle vs relying on the plex system to flash the lights?


Under part throttle the background noise level will be lower than a WOT ramp run, so yes, the sensitivity or ability of the unit to detect knock based off the threshold can be reduced. Typically a knock event will result in a pretty significant spike in noise though so it will usually still register. Even if it's under the threshold, a knock event will result in irregularities in the noise trace that can indicate you need to look closer (listen closer) to what's going on.

Realistically just continue using the audio aspect at the same time and then you've got your bases covered.

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