A request to the technical experts among you:

Who has experience with using RON 95 and RON 98 octane (EU figures) with regard to engine knock of the 5-cylinder engine generation?

My experience: Using 95 RON and accelerating in 2nd or 3rd gear (MT normal aspirated) from about 1000-1500 rpm, you can clearly hear the anharmonic knock sound. (Btw: you can only hear it when the window is open). Using 98 RON under same conditions there is no knock audible.
I know that for the ECU to react, the knock sensor must first detect knock, before the ECU retards ignition. Is that what I actually was hearing?

How do you know the knock sensor is really working?
Is it normal that you can actually HEAR the knocking before the ECU reacts?
Is there one or two for the five cylinder engine?
Is the ECU able to recognize failure of a knock sensor?

Thanks in advance for your comments!

You'd have a check engine light if there was a faulty signal from the knock sensors. That was a problem with the 850s, replace both sensor and the wiring harness. We've never seen a problem with anything 98 or newer.

Thanks Chris, I'm aware of that.

There are no warning messages on the display (and also no VADIS fault messages after read out by the dealer).

The main thing I want to know is if it is normal that you actually HEAR the engine knocking for a seconds or so under the conditions I wrote in the original mail:

"My experience: Using 95 RON and accelerating in 2nd or 3rd gear (MT normal aspirated) from about 1000-1500 rpm, you can clearly hear the anharmonic knock sound. (Btw: you can only hear it when the window is open). Using 98 RON under same conditions there is no knock audible".

Greetings,

Dutchman