I found a formula for the frquency at which knock occurs. Can any of you electronics gurus build a simple detctor box for a set freqency range.

the formula is

detonation resonant freq=900/(3.14*cylinder radius)

cylinder radius is in meters


for a stock piston evo that would be:900/(3.14*.085) = 3372.049Hz

I know there are different methods to listen to knock, I want something that can filter and listen to a narrower frequency range.

 

knock frequency changes depending on the RPM etc...
anyways, your wanting to build a band pass filter which is really easy to do. just search on the internet. I could build them for you but you can do it much cheaper than I would sell them.
good luck.

 

why not use tephra's knock patch? uses the stock ECU's knock control program and warns you by flashing the SES light.

 

Please excuse my ignorance, may I ask dummy question? Where does the magic number 900 come from?

 

I am not sure of the formula, but this makes sense. Its like plucking one string on a guitar, if your equation ends up being a High E you will always hear a High E when you pluck it. IT would be a tuned frequency based on the amount of space in the cylinder for the knock to resonate.

This actually has more application for the standalone guys that have voltage based knock control and not frequency based (other than VI-Pec). Where did you find this formula?

aaron

 

The question is just what orientation is the string at which moment and how long it is, so my question reformulated means what has been hidden in 900.

 

Here is a Homemade Knock Detector we found in the trunk of one of our customer cars.




It had a T-fitting and a 10 foot length of clear braided that ran from something on the side of the block, into the drivers compartment. I am not kidding. The really cute guy in the picture is me, modeling this new technology at work.

/brox

 

Here is the page I found it on: http://www.autospeed.com/cms/A_0348/article.html

^^That homemade knock detector will actually work pretty well. Before ECU's had fancy knock detection built in thats how people used tune.

 

That is pretty funny looking for sure

 

You will be attempting to engineer something already existing in the ecu which is accurate (except all the filters that become off-tune once parts (i.e., cams) are bolted on).

 

Maybe there is some way to have sound output from stock microphone ?