Forum » General Tuning Discussion » Plex knock monitor users

Plex knock monitor users

General Tuning Discussion

Discuss all things tuning in this section. News, products, problems and results. 

Page 1

Hello fellow tuners,

So I'm still trying to really get the hang of this system. Quick question for all you guys using it with rpm signal, and using the threshold graph.

So hypothetically speaking let's say you're tuning a turbo 4 cylinder. Using the supplied basemap. Go in and remove 2 degrees out the entire map in positive boost pressure. Start off with 10psi wastegate spring pressure. Do a full pull, (of course monitoring AFR and confirming they good.) While listening to the audio in the plex and confirming no knock, that builds the audio noise level of engine. So put the knock threshold slightly above it. Cool? then the 10psi noise level is set do your tuning.

But what are you guys doing when increasing boost pressures, when let's say you're at 18psi. Is one suppose to create a new floor or base noise level every time boost pressure is increased? And listen for Knock in the audio at all times? That's the part I'm a bit at a loss. The engine becomes so noisy compared to 10psi that the threshold one creates at 10psi technically is no good for 18psi of boost pressure right? Or naw? Hope this makes sense what I'm trying to ask.

This is a good question.

Did you also watch the webinar about the Plex Knock Monitor V2?

My understanding is as follows:

Basically, you want to set the threshold line as close as safely possible to the actual running condition you will tune the engine in, in your case 18psi. Probably 15 or 16 psi and ignition in the region which is realistic but safe should also be fine for your particular engine.

Setting the line at 10 psi is obviously not very close.

Yeah I watched the video. Seen it like 5 times now. He does a great job of explaining the system on how it works and the settings to use and features and all. But you know. When you use it you end up having questions.

But just wondering. Is what I'm saying a thing? And if so is their a general rule of thumb of when a new threshold of noise level should be adjusted? Or simple a no just forget the graph and use your ears? Or setup the graph and that's that. Anything above it is real knock?

I know Andre says an engine that is getting to a point of ignition advanced and making power will generally make more engine noise that the sensors will pick up. This tells me maybe i should be setting a new noise level threshold. But am i right? Is that what these pro tuner users are doing? Or no don't dare to Do that?

G'day Daniel. Have you made any WOT runs at your increased boost level?

My experience is that the engine certainly gets noisier as it starts producing more torque, particularly with more boost, but the increased noise is at different frequencies to that of knock... Plus, your knock events get louder too. I'm not completely familiar with the digital filtering in the Plex units (I'm going to see if I can pinch the one here for the weekend to get more familiar with it), but I would hope that it can filter a lot of the increased engine noise (turbo whooooosh) out.

I'd do a WOT run on your increased boost level and original noise profile, listening to the audio. If you find the Plex is telling you you're having knock events, but you cannot hear any actually happening, you'll need to re-visit your noise profile for sure.

That's probably not too helpful, but let us know how you get on, really interested to hear.

Sadly I did not happen to take any pictures of the plex unit when doing this. But yes I did encounter that at more boost pressure my scatter plot of dots would rise above my base floor level for noise, but in the audio their was no knock bring heard. The plot would be higher only in the area of motor making boost, so essential 4k and above.

My understanding of the unit is it's plotting noise frequencies and yes essentially if more boost pressure, in theory it should plot the noise level a little higher as it gets closer to the frequency of knock itself? I Don't know really. Maybe i didnt give enough space between my floor at 10psi ?

I'm just not sure and well being here in California where our best fuel is. 91 octane. I'm truly always very extremely cautious with knock. And the reason why I wanted the best knock detection unit in the market. But the struggle is real with it. Haha.

Hope you get a chance to mess around with the unit Zac. Really would love more input.

I emailed Plex tuning about this question. Still no reply. Anybody have anything they would like to share? I'll share the email response when received.

If you're sure you're not encountering knock at your higher boost level, I'd adjust the noise profile in the plex to just above the noise of the engine at this higher boost level. By doing the WOT runs at this higher boost, with safe ignition timing, you've created a base line profile for how the motor sounds without knock, so you can now start increasing the timing and any knock should register. Make sure you're still listening through the headphone jack all the time though, the digital knock interfaces are great, but nothing beats your ears for detecting knock :-).

Thanks for the input Zac. ✌

I might have a better idea after this weekend if I can pinch the Plex V1 from here again. Didn't get a chance to have a play with it last weekend, I was too busy fitting sick rims to my truck instead ;-).

Crikey, how many Plexes do you guys have a HPA labs?!


But, no, a V2 on the remote dyno rig, and a v1 used for general purposes :-).

I have a V2 and still learning but I think I got it figured out. As mentioned the engine noise increases with load and as it graphs out on the plex, it is an upward curve. so if you hit 10psi threshold will be at one level. when you hit 18psi it may be at another level. From what I've seen knock noises will be well outside of the cluster of data, of course corroborated with headphones.

My approach though, would be to tune at incremental boost levels, 10, 12, 14, 16, 18. Tune for afr and ignition while listening for knock at each incremental level throughout the entire rev range to make sure you everything is good at that boost level and updating the threshold as necessary. Depending on your ECU, I am also adjusting its knock threshold. Doing it that way you can become familiar with how the engine noise increases in a slow controlled manner.


Plex V2 user here too.

generally speaking, the noise floor increases with dynamic compression so the more power you make, the louder it is. I liken a cylinder to a trumpet... the harder we blow, the louder the sound, so that is pretty much a given.

You should find that once you have you noise floor programmed and start to wind spark in, it will still get "louder" but if all is going to plan you will SEE knock as entries firing in WAY up above your noise floor.

Ive enclosed an image of a pull I did to demonstrate this in some other discussion a few years ago.

Attached Files

This is all such great information from everyone ! Thank you all.

I have been using my Plex Knock Monitor V2 on several vehicles now and am still very pleased with it.

Especially the audio output is great and I have the best results with the 5 kHz high pass filter. The knock I hear is so nice and clear and you can't miss it. Really valuable tool.

:) even time i see a plex post...

the more you use it and play with the better you will understand and your car at the same time.