Outer Limits 4x4 Board

Just wonding if anyone has used with much sucsess such a devive like the" Knock box" (very expensive)or even a rubber hose from a metal connection point to a set of ear muffs to listen to engine knock while under load. There is another way for detection that i'm going to try, costs $15 by using a personal hearing aid devive with head phones then taking out the microphone and attaching to engine via aligator clip to listen to engine pinging/ knock and detonation. You can even hook up this to a knock senser where the microphone wire's in to listen as well. Just after a cheap tuning aid for boost and timing to see how far you can push it before going BANG!

You can buy a mechanic's stethoscope, similar to the ones doctors use.

or u could buy a air fuel ratio gauge, and or get ur engine tuned properly on a dyno

Nah, I have a A/R meter, I'd be there all the time, I'm constantly changing the set up and with different fuels in the future. Want to tune it my self and not rely on someone else's idea of good tune.

tufftruckin wrote:or u could buy a air fuel ratio gauge, and or get ur engine tuned properly on a dyno

There's more to engine knocking than air/fuel ratio, and a dyno can only tune to the conditions on the day.

Modern engines don't use knock sensors for the hell of it.

There's a lot of development that goes into knock sensor systems, location on engine sensor type / tuning etc etc - so even a 'dumb" microphone can be difficult to place without getting overwhelmed with normal engine noises.

Manufactureres use spectrum analysis systems to spot the knock signature and then DSP systems to detect it electronically... complex stuff, and its usually caught at the trace detonation level before you can hear it.

Still if you can find the right spot then even by ear its not that hard to pick significant detonation before you would normally hear it so its worth trying.
If your really keen you can record the noise to a wav file on a PC and use any of the Freeware spectrum analysis programs to see where the audible signature is located frequency wise. This is done by developers so its effective if you really wan't to head down that path.

Adjustable filters to eliminate noise outside the range of interest help but it is pretty hit and miss without doing as suggested above.

I've tried one of the cheap "knock sensor" kits and it didn't really work as it couldnt discrimate between normal engine noise and knock.

The knock senser kit you tried, was it to retard ignition or activate warning lights. If so it is very hard to tell a electronic module the difference between engine knock, valve train gear, crank shaft wooble even piston slap. With all these box's and computer's out there claiming they detect ping and detonation better than the human ear is crap. A dyno operator with a head set on listening to the engine under loads will hear pinging/det way before a electronic box can because they can only detect the frequency the knock senser is tuned for (about 6500 KHZ ) and a margin for error built in to stop it going off all the time.

It was just a "detector" and was pretty rubbish but as a mate built it, I though it would be interesting.

As for the ear being better than electronics - i'd disagree. A properly developed knock sensor system can detect sub audible ( i.e. onset detonation ).
I'm not suggesting that this is possible with a microphone, and a $20 electronic kit, rather a properly engineered system.

As for system tuning, that's a matter of sensor design, some are mechanically resonant at the frequency of primary interest for a specific engine which means they may not be suitable for alternative applications. Others are untuned and rely on Digital Signal Processors which look for a frequency/amplitude detonation signature.

Margin of error isn't the strategy used by OE's - they continually let the engine drift towards trace detonation and then pull back. Because they are detecting onset detonation this results in optimum tuning without engine damage.

I use the "Knock box" combined with a set of Aviation noise cancelling headphones. When used correctly it is brilliant, I can hear knock clearly over all engine noise, superchargers, screamer pipes and so on. The mounting location of the sensor is important as is the setting of the filter level. I have the upgraded Knock box that runs 2 sensors simultanoeusly if you want to mount to each bank of a V8 or front and rear of an inline 6.
It means I can tune without having to pull other guys off the floor to listen for knock.

Joel

If I had the cash thats exactly the set up i'd use. Also heard the Gizzmo Kmon set is preety good two. Is the Knock Box made in AUS? who is the distributer?

I got mine through Wolf as we are a dealer for wolf and the headset is specific to them, the standard one supplied is not of the same standard as the aviation one supplied by Wolf.

Joel

Here's my super expensive $7 knock detector I made off the internet using a personal hearing aid with extended microphone attached to aligator clip. It works supprisingly well, can here valve train operation and annoyingly ignition pulses. Yet to hear a ping or knock bugger it, tried advancing the initial to 30deg and loaded it in low rpm to get a knock with out blowing a gasket and no go. Going to put it on my wifes car as that pings down low to get an idea of the sound. Let ya know how it go's. I know it's not going to be anywhere near as good as the professional unit but For $7 bucks I had to try it.

I used to use snap on Chassis ears which have all the issues you described but found with some audio software off the internet I was able to filter a lot of the juck noise out. The problem was the 50 ms delay. I couldn't find a true real time filter

knock link

http://www.tuspeed.com/product_info.php ... b9a1d2376d