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False knock vs real knock on Knock headphone

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Hi Andre I have a question about false knock vs real knock when using the headphones because the last time you demonstrated this was only real knock on the webinar. What does a false knock sound like on the Headphone, i mean don't they all sound a like if the frequency is being picked up knock sensor they should all sound same on the headphone?

You won't/can't hear false knock. When I use the term false knock, I'm talking about a knock event that the ECU detected that wasn't happening audibly.

Sorry Andre confused about this part If we cant hear the false knock on the headphone, how does the ECU knock sensor hear the noise?

I thought the knock sensor just picks up noise and so does the knock headphone so why the knock ear phone cant hear false knock but ecu knock sensor can ?

False knock can be induced in the detection system by mechanical noise of the engine as well as other variables. The knock detection equipment is simply relying on the parameters we configure to determine what knock is. With headphones you are able to decipher what a true knock event is and tune the sensitivity of the knock detection system to minimize the effect of background noise.

For example, an engine with solid lifters that have not been clearanced correctly can create a "knocking" noise which increases frequency with engine rpm , the knock detector will detect this noise and report knock while there is no actual detonation taking place.

Hi RBS14 Is it easy to distinguish between your example of lifters that have not been clearance on the knock ear phone vs real knock? Does this take lot of experience to identify noise being real knock or false to tune it out ? or it is something very easy to distinguish between the 2 when u are using knock ears?

RBS14 has summed it up pretty well. The ECU's knock detection strategy is looking at a certain frequency and a certain level. If the input exceeds this then the ECU determines the input as knock. Depending on the engine and its noise profile this may or may not be the case though. It's less of an issue on a stock engine but can become a real problem on mechanically modified engines.

Determining the difference between knock and engine noise through a head set can still be challenging in some instances. It takes some experience and on very noisy engines I still struggle occasionally. My advice in these instances is to try inducing some actual knock on purpose so you can determine what that sounds like through the head set.

If you have the ability to set the actual frequencies that the ECU monitors for knock, you are better off to use the second order frequencies for the knock system, this will move the monitored frequency above the general noise of the engine and help to avoid "false" knock being detected.

Hi Black Rex sorry I do not understand what second order frequencies mean can you explain a little more?

I get raising monitor Frequency above the general noise but what do you mean by second order frequencies?

If the actual knock frequency is 7500hz, then the second order value will be 15000hz. It is a doubling of the value, and helps to move it up out of the noise of the engine.

Thanks got it

People use the term "False Knock" respectively "False Detonation" differently. The way Andre uses it refers to a audible / visible indication on the tuning equipment. Another way these terms are used is during the fault-finding process after damage has occurred without any traces of detonation:

"Adjusting the timing to maximize power can generate other issues such as detonation and "false detonation". Simply put false detonation is when the engine suffers catastrophic failure and the tuner assumes it blew up from detonation when in fact combustion was smooth and detonation did not occur. Supercharged engines can develop extremely high peak combustion pressures when properly adjusted and unless the engine is capable of supporting these pressures engine failure may occur without detonation occurring."


Just for clarification regarding the second order knock frequency that BlackRex has mentioned, this is not generally something you will have the ability to adjust in an OE reflash system - I haven't come across any reflash software where the knock frequency is adjustable. It's a very valid point in standalone ECUs though and it's all about optimising the signal to noise ratio so you can better distinguish a knock event.

In a standalone ECU the knock control system needs to allow a lot of end user tuneability because the same ECU may be expected to function well on a wide range of engines. In an OE situation though often most of the hard work is done by the factory engineers as the ECU only needs to detect knock on one engine so everything is optimised around this. Often late model engines are fitted with narrow band knock sensors that are tuned or optimised for the second order knock frequency too.


From what you explained, are you referring to the rising rate of cylinder pressure after the spark event in comparison to piston speed? Can this described instance be considered an example of what you were talking about?

Secondly, from an ethical stand point, would an engine calibrator be hold responsible for overcoming the structural integrity of the engine and its internal parts? Everyone and his dog has a "built engine" these days and "balanced & blue printed" is a standard which gets tossed around a fair bit, so mechanical failure which would occur from either weak parts (sometimes inferior parts) or horsepower potential overcoming the strength of the engine can be the fault of the calibrator?

Any calibrator want to chime in here?

Andre, would it be a correct advisory to be versed in some level of engine building, materials and the effects of shearing stresses on them or at the very least the post mortem analysis of damaged engines?

It's a tricky question you raise @sardengineering. I've broken my share of engines over my time as any tuner pushing boundaries will have undoubtedly done - Nobody is immune. I also had the advantage that I simultaneously learnt about engine tuning and engine building at the start of my career so I guess I had a slightly broader knowledge of the entire process than some. It's definitely not essential though.

Who is responsible for a broken engine is always a messy debate. I believe it depends what the customer wants. For example if I'm tuning a drag engine and the owner wants to push the limits then component failure comes with the territory and as long as they understand the risks then it's on their head. The tuner shouldn't run the engine lean or cause it to detonate, however if you exceed the component strength in the quest for maximum power then that's a different story.

If the customer would be put out financially by an engine failure and is a little more conservative then I'll adjust my approach to suit and this may involve leaving some power potential on the table. Of course this demands some level of knowledge of what a specific engine can cope with. Some of this comes with personal experience or alternatively it can come from research and talking to other trusted professionals well versed in that particular engine. I'd always take dyno numbers found on forums with a grain of salt personally.