The frequency at which knock occurs depends mostly on piston diameter and in-cylinder temperature. There are two types of piezoelectric knock sensors: tuned (resonant) and broadband (non-resonant). Tuned sensors are factory-set to amplify the signal only around the desired frequency range, while significantly reducing the rest of the frequency spectrum. While ECUs using older technology which lack signal processing capabilities require this, our ECUs function best on broadband sensor, a sensor which captures the signal in its entirety and can be used in any engine configuration.


Suitable sensors include the Bosch one available on the Motorsport Electronics webstore.


We’ll start by examining the knock signal coming from the sensor. In exactly the same way as a microphone converts your voice into an electrical signal, a broadband knock sensor will pick up the vibrations produced by the engine while functioning and convert them into an electrical signal. Because of the different intervals and moments in time when each event in the engine happens, all these noises and vibrations are distributed over a wider range of frequencies. 


The knock signal processing component of the ECU then has to correctly isolate the signal around the knock frequency and monitor its value. When it goes above a certain threshold, the engine is knocking.