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I just watched a webinar on seting up the Knock detection strategy (on Motec M1 i think).
I understood that the first thing to do is to find the frequency signature of your particular engine (ie the frequency at witch there is the biggest knock activity amplitude in order to easily detect knock)
My question is : Is that frenquecy totally independant on RPM and Load ? I understood it's mainly relative to the piston bore diameter, but does it varies with load and engine speed ??
Thanks in advance !
The frequency is independent of load and RPM, but the amplitude of the signal is not. That's why the thresholds for knock varies with RPM.
The frequency is dependent on the bore diameter. However the strength of the "normal" (without knock) noise in the engine rises with engine load. if you use audio knock equipment you can train your ears in recognizing knock from other noise.
if you're first starting out with audio equipment try to start without to much frequency filtering.