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Plex KM V2 - stacking sensors and bore size?

Practical Standalone Tuning

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The Plex Knock Monitor V2 webinar was fantastic, and I learned a lot.

However, it didn't answer all of my questions, so here goes:

1) Can I stack sensors?

- i.e. place the Plex sensors on top of the ones used by the ECU (Holley Dominator)

2) Which is more accurate, the knock frequency provided by Plex, or one based on the formula provided in the video?

- My bore size is 4.31", or 109.474mm.

- The Plex offers a frequency of 5,680 Hz for 110mm bore size.

- However, the frequency derived from the calculation that Andre provided in the video is: 1,800/(3.142 * 109.474) = 5,233 Hz.

- Therefore, a more precise bore size choice in the Plex offerings would seem to be 120mm, or 5,290 Hz.

Lastly, I'm confused by the vast difference between banks. The attached was captured using the Plex supplied sensors installed in the stock location (down near the pan rail in the center of each bank). Note how bank 2 shows very little knock level.

Edit: I'm just beginning to use the Plex KM here, and haven't done much other than adjust the threshold. Also, this is NOT a max effort engine build, and at 8.7:1 NA it is not likely knock limited.

About bank 1 noise level, that sensor is much closer to a header primary tube than the bank 2 sensor.

Attached Files

So, the 120mm frequency seemed to provide the cleanest/smoothest knock level, and I ended up using 5.3kHz in the Dominator ECU. So far so good, i.e. no more false knock.

I ended up putting the driver side (I mean left side) Plex KS on a different stud. As for the low knock level from the right side KS, it turns out they are not wireless!

Attached Files

Yes you can stack sensors.

HPA suggest using twice the frequency to get a better signal to noise ratio. More on that here:


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