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Stacking 2 knock sensors

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Hey Andre/Zac,

Can you guys or anyone else with knowledge on this please tell me if you stack two knock sensors one on top the other if there will be any sacrifice in the accuracy of the output from the knock sensors?

Say for instance you are tuning an engine and you have a secondary means of detecting knock, say a plex knock monitor. You remove the oem knock sensor and place the plex knock sensor in its position. You then get a longer bolt and replace the oem sensor ontop of the plex sensor and tighten everything up.

Would either sensor be compromised?



Hey Chris, it's hard to give an accurate answer since I haven't tried this myself. I would be concerned about how well the engine vibration would transfer into the second knock sensor compared to having the sensor mounted flat to the engine block and for this reason I wouldn't probably recommend it. Ultimately the only way to know for sure is to test it out and I'd do a back to back test between stacking the sensors and having them individually mounted to the block. If you do, please share your results.

In closing though, I'm not sure I've ever been in a situation where I couldn't find a suitable boss on the block or head to use so that would always be my first suggestion.

Hi Andre, it's for an Evo X and the current head position is less than ideal especially for me as a novice tuner that doesn't have much experience with my Plex knock monitor listening to different engines.

I'll report back on my testing, thanks.

Chris, you ever got this sorted?

How has the plex worked for you?

Greetings, old thread i know but i believe i can add to the discussion since this is the first post that comes up on the forum or on google.

We are running a link g4+ xtreme with knock monitoring and ign control, and knock monitor v2 just for waveform analysis.

i've made a small test to see the response of the second knock sensors, i've used two new Linkecu knock sensors, mounted the first on an empty aluminum block, and mounted the second on top of it (stacked using the same screw).

First thing to note is that the surface area that the second sensor is touching i considerably smaller than what the first sensor is touching.

After that i connected the sensors to an Oscilloscope.

CH1-Yellow is mounted on the block

CH2-Cyan is stacked over the first.

For the first test i hit the block with a hammer and measured the signal, the one touching the block always gave significantly higher reading than the stacked sensor.(check attached)

For the second test i subjected the block to a sine wave @41hz, the sensor touching the block gave higher reading but i believe by setting the correct gain both will function as required.(check attached)

i will be doing an actual test on the engine dyno, also i will be designing and machining an adapter to connect two sensors next to each other on a single mount, i believe this should increase the surface area and deliver the same signal amplitude. Will post the results.

Thank you

Attached Files

I suspect proper coupling and mounting bolt torque etc that is mentioned in most documentation is more critical when you are dealing with an OEM ecu with little adjustment available for the gains and other characteristics. Since you have two devices that you can adjust yourself I dont see any reason why this wont work. The only thing I would be a little worried about is the output signature from the "bottom" sensor may change if you later remove the stacked sensor after tuning. So make sure you verify you are getting similar knock levels reported after removing the stacked sensor.

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