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Knock sensitivity of engines based on gear

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I've had my Plex knock monitor connected to my car and listening while I drive and I found something a little strange. I did a third gear pull, heard no knock but then went to 4th and started hearing knock at points through the rev range that I previously didn't hear in 3rd gear.

For the experienced guys.....is this something normal? And due to the engine being under more "load" in the higher gear?

Yes this is quite normal in an engine that's quite knock sensitive. In higher gears there is more load being applied to the engine and the engine accelerates more slowly through the rev range. The result of this is that more heat is generated in the combustion chamber which makes the engine more likely to knock.

Generally on an engine that's knock limited I tend to do a longer ramp run on the dyno to simulate running in the higher gears. If I can tune the engine to be knock-free under these conditions then I can be reasonably confident that the engine will also be knock free under race conditions.

Agree with Andre, to add to that, sometimes after I do a long run in say 3rd gear and there is no knock but is under 4th or 5th I will setup another table to have timing removed per gear. Then remove around 2 degrees in 4th and maybe 3 in 5th etc.

It's not often I will do this and when I do you need to ensure you get it set right and it won't knock in any gears. Sometimes it is just worth removing the timing and sacrifice the additional 10kw or so.

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