Electronic Solutions for Motorsport

Lift Off Engine Knock – Load Threshold

2 min read

One of the features that has been added to the KSC3 is user definable load threshold, below which any engine knock signals are ignored, the purpose of this feature is the limit lift off knock being reported as engine knock.

There is some discussion on forums (here, here and here for example) on whether the knock being reported when lifting the throttle is real or not. I think Andre at HPA (first link) sums up the MoviChip position, namely the conditions in the engine are not conducive to knock when the throttle is lifted because there is a big vacuum in the inlet manifold, meaning cylinder filling is low, which is not a situation where knock would be expected.

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The purpose of this post is not to tell you if the lift off engine knock reported by the KSC3 on lift off is real or not, you have to make that decision according to your experience and situation. The purpose of this post is to highlight the load threshold feature in the KSC3.

If you believe the knock being reported on lifting the throttle is not engine knock, the KSC3 load threshold feature allows the user to tell the KSC3 to ignore any knock signal that occurs below the user defined load threshold.

Whether the user wants to use this feature is entirely up to them

At MoviChip, when the load threshold is set, a number slightly above idle vacuum is used, the thinking being, as described above, is that cylinder filling will be very low when the inlet manifold is experiencing close to idle levels of vacuum.

If you are not sure whether the engine is actually knocking when the throttle is lifted then by all means, set the threshold to the lowest possible setting.

If you are sure the engine is not detonating when you lift the throttle, then set the load threshold to a number that suits you.


But again, be aware, the KSC3 will essentially be switched off when the engine load does not exceed the load threshold set on the KSC3 unit.

As always, the KSC3 should not be and it is not designed to be a device that protects the engine from detonation/knock. It is a tool to help identify knock and should be used in conjunction with other methods to safeguard the engine eg microphone in the engine bay/headphones plumbed into the knock sensor and so on.

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