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Introduction to Engine Tuning: Knock Detection

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Knock Detection

03.03

00:00 - Given the damage that knock can cause, manufacturers have been including knock detection and control systems on their ECUs for many years.
00:09 This includes both factory-fitted ECUs and those in the after-market.
00:14 The idea behind these systems is to include a sensor fitted to the block that can pick up the vibrations associated with knock occurring.
00:23 From here the ECU can process this data and if it decides that knock is occurring it can retard the ignition timing to help safe guard the engine.
00:33 These systems can be very powerful and particularly with the newest generation of ECUs, knock detection and control can be surprisingly accurate and effective.
00:44 When we start to modify the engine though, this can change the noise profile that the engine produces which is essentially what the knock sensor is listening to.
00:55 This means that on a heavily modified engine the knock control system may struggle to accurately detect knock.
01:02 This is potentially a big problem if you're relying on the knock control system to keep your engine in one piece.
01:09 I've also struck some engines that were completely stock yet for some reason the knock control system was falsely indicating that the engine was suffering from knock.
01:19 This sort of situation is safe enough as it's unlikely to result in engine damage.
01:25 However, the ECU will be retarding ignition timing in response to what it thinks is knock occurring and hence, you're probably going to be leaving some power on the table as a result.
01:37 More dangerous however, is the situation where the engine actually is suffering from knock and the ECU isn't able to pick this up.
01:45 I've seen this situation numerous times.
01:48 So, blindly assuming that the ECU is able to do its job as intended can sometimes be a dangerous assumption to make.
01:57 For those reasons I always like to use audio knock detection equipment when tuning any engine.
02:03 And we'll discuss what this is and how it works shortly.
02:07 It's important to understand that a knock control system isn't there as a substitute for correctly tuning the engine.
02:16 Instead it's there as a safety backstop in case you end up with a bad batch of fuel with a low octane rating or perhaps the engines operating conditions end up vastly outside those that were experienced when the engine was tuned.
02:31 In particular, the knock control system is reactive not proactive.
02:36 This means it can't do anything until knock actually occurs.
02:41 While minor levels of intermittent knock are unlikely to cause damage immediately in a low or moderately powered engine, in highly tuned engines, knock can be very damaging very quickly.