I was going to buy the Knock Link today and saw it online and decided I thought it was too simple to pay money for so I will build my own. I am assuming all it does it light up certain LED's depending on the voltage produced by the knock sensor. I was wondering if someone could tell me what the knock voltages are while WOT with no knock so that way I could make sure I use the correct resistors to light up my LED's and make sure I know where real knock is as apposed to regular engine noise. Thanks! I could also use the someones EMS knock table I would think.

 

TrinaBabe I would like to help you out since we kind of had a similar discussion on this. The stock knock sensor reads up to 5volts but as you allready know each car is different. What you should do is log your voltage with you datalogger if you can so see its normal trend, you will need to log at a very high sample rate probably 250 samples per second to see everything. When you car knocks the voltage will spike usually 1volt or more over the normal noise trend this way you can get as close as possible. I have my car setup very consertively and my noise knock table is set at .4 volts from 0 to 2400 rpm then it runs an even increase and settles at 2volts at 7200 rpm and never goes any higher. I set this table by listening to the engine in several modes such as neutral revs , low boost low timming revs and slowly increased th a heaver load so it could be taken into account and logging the raw knock noise trend voltage output and the knock noise trend sampled at the time of ignition for the real value. I would say it would be very hard for you to set a table on your car perfectly without being able to log its trend effectively because of differences in each car but you could probably get close enought for what you are looking for after some work. I hope it helps atleast give you a little bit of what to expect and some settings to start with. Good luck.

 

thanks, that will help me out but what tool can I use to datalog my car better for a relatively cheap rate? Right now I have the ELM based logger which blows donkey ***. It is relatively worthless, I get about 4 sample a second on one variable... 2 samples/sec with 2 and 1 samples per sec with 4 var's. I have heard the different chipset's on datalogging cables are capable of getting 40-50 samples/sec (like autotap's). Is this true? Otherwise what else would you recommend for getting a better sample rate? Thanks

 

Well I have been doing some looking and I can't seem to find any datalogger that samples that fast. The only thing I have even seen that might be able to get you close is the PLX wideband and datalogger unit. They don't give exact details on it so I would email them and ask just to be sure before purchasing. I have done testing on my EMS logging at slower speeds and it will pick up knock but not every time. At 250 samples per sec it picks it up 90+ percent of the time. The plx unit is about 500 bucks and I have posted a link below. I haven't heard of autotaps but I haven't paid much attention since just deciding to go to a standalone to have the entire package and be done, other wise I was going to spend just as much money and everything else seperate. I would think that there has to be somthing out there so hopefully others will chime in. But if not it would explain why people are using the knock link device. Probably so far the best totally for sure way of knowing but I can't speak for it becuase I have never used it. If I run across somthing I will post it.

http://www.plxdevices.com/M-Series_l...roductinfo.htm

 

AFAIK, the knock sensor doesn't just output a simple voltage. Most knock sensors are tuned microphones that "listen" to the engine. The stock ECU then conditions this signal to convert it to a voltage level proportional to the amount of knock. See this page: http://home.netcom.com/~bsundahl/kno...nockSounds.htm for some logging that a guy did on his 4G63 motor.

I'm in the process of adding knock logging to my engine management doohickie, the ECU+. If just logging voltage was enough, I'd already be done!

Tom