Electronic Solutions for Motorsport

Knock Detection Threshold vs Engine Load – Necessary?

2 min read
Knock sensor on wooden table

How important is it to have an engine knock detection system which takes into consideration engine load?

In our experience measuring engine knock against engine load is a nice-to-have but not an essential.

The MoviChip KSC2 has a variable knock threshold vs RPM but not vs engine load.

We found that when setting up the KSC2, specifically setting up the knock volume thresholds at WOT, the KSC2 will still pick up engine knock at part throttle at the same RPM point.

The difference in the volume of the knock frequency between knock and no-knock conditions is so large that it overcomes the difference in volume between knock at part throttle and knock at full throttle.

To put it another way, there is a difference the knock volume when we compare part throttle and full throttle but that difference is much smaller than the difference in volume of the knock frequency when we compare no-knock conditions with knock conditions.

Again, it would be nice to be able to tailor the knock threshold volume according to engine load but it does bring some negatives notably in the extra complication of setting up the knock thresholds in the app for the end user.

Engine Load included in future versions of the KSC?

On balance, the answer is probably no. It is already been said twice in this article but the point is worth reiterating.

When an engine is running normally/correctly ie not knocking, the volume of the noise in the knock frequency window is relatively low. When the engine does knock, the volume of the noise in the knock detection frequency window can double if not more.

On the other hand, the knock volume difference between part throttle and full throttle is usually not 100%.

It doesn’t seem as if adding engine load to the knock threshold settings is going to improve knock detection accuracy. The complications of adding a variable knock threshold according to engine load looks to far outweigh any benefits that may come.

Are We Interested In Detecting Knock @ Part Throttle?

Absolutely. Experience suggests the KSC2 can detect engine knock just as well at part throttle as it does at wide open throttle and this is why we are not adding engine load to the threshold calculations, there does not appear to be a need.

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