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Introduction to Engine Tuning: How to listen for knock?

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How to listen for knock?


00:00 - While the ECU's knock detection system can be very effective, as we've just found, it can't always be relied on when we start modifying the engine.
00:09 For this reason I always recommend using audio knock detection when tuning any engine so that the tuner can confirm when the engine is suffering from knock.
00:20 Audio knock detection systems are stand alone systems that operate outside of the ECU's own knock detection system and are usually just fitted to the engine temporarily for the tuning process.
00:34 We start with a knock sensor which is bolted to the engine block and picks up the vibrations associated with knock occurring.
00:42 A knock sensor is a piezo electric sensor that converts vibration into an electric signal.
00:49 The only trouble is that the engine is inherently a mechanically noisy environment and there are a lot of vibrations created that are related to normal engine operation instead of knock.
01:01 In order for the knock audio system to filter out this background engine noise the signal from the sensor is fed into a digital signal processor that can focus on the frequency that knock occurs at.
01:15 From here we can plug a set of headphones into the signal processor and audibly listen for knock occurring.
01:23 You will still be able to hear some of the normal mechanical background noise occurring but with a high quality audio knock detection system you should be able to easily distinguish between normal engine noise and the sound that occurs when knock happens.
01:39 This is an essential tool to aid in engine tuning and if your ECU is equipped with built in knock detection it can also be used to confirm that this knock detection system is functioning correctly.
01:53 So that you know what to expect here's an audio recording of an engine that is knocking using the Plex Knock Monitor.

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