Well I picked up a data acquisition setup back in 2006 to do some testing with the MAF sensor. I never did it. I finally dusted off the data acquisition, which by the way is a DATAQ - DI-148U. Anyway, I hooked up the stock Legacy knock sensor and the WRX knock sensor to it, and recorded their response curves.
Some general comments about the data. The Legacy sensor appears to be more sensitive. However the data from the WRX sensor looks a little cleaner. Someone with some more experience may be able to provide some additional/better comments on the data.
For the test setup, I originally had the Legacy sensor in the stock location, but then moved it to a spot on the bell housing along with the WRX knock sensor. I also did some testing with the sensors on the Impreza with the engine running. I had to place them on the Impreza one at a time. They were placed on the rear bell housing as well. Here are some pictures of the test setup.
https://www.main.experiencetherave.com/ ... testsetup/
For the data plots, the first ones are at a lower sampling rate. I started at 1,000 Hz, and went all the way up to 14,000 Hz. One thing to note, for the plots with both sensors hooked up the actual sampling rate for each sensor is half the sampling rate displayed on the graph. The sampling rate I note is the rate that each knock sensor was sampled at.
For the notes on where I struck the knock sensor. When it notes that I hit the knock sensor, I hit the top of the bolt holding the knock sensor into the block with a hammer. When I hit the front of the block, almost all the time I hit the block in the center where the two halfs come together and the piston sizes are noted. For the rear of the block, I hit primarily the flat part on the bell housing near where the starter bolts in. When it notes I hit the knock sensor spot, I hit the stock mounting spot on the block for the knock sensor.
Ok, onto the data curves. I'll try to provide some comments for each graph. For all the graphs with two curves, the Legacy knock sensor is on the top graph, and the WRX knock sensor is on the bottom.
(Click on the images for higher resolution pictures)
Legacy Knock Sensor Hit 1 – 1,000 Hz
Legacy Knock Sensor Hit 2 – 1,000 Hz
WRX Knock Sensor Hit 1 – 1,000 Hz
WRX Knock Sensor Hit 2 – 1,000 Hz
WRX Knock Sensor Multi Hit 3 – 1,000 Hz
This one just had multiple hits of the hammer. Interestingly, you can see how the Legacy knock sensor has more transient oscillations, even though the peaks are less than the WRX knock sensor.
Block Multi Hit 1 – 1,000 Hz
You might be able to argue the Legacy knock sensor was closer to the point of impact with the hammer, but the peaks are drastically larger in most cases. So either the Legacy sensor is way more sensitive or possibly tuned better to the block, or the placement wasn’t right with the WRX knock sensor.
Block Multi Hit 2 (2nd location) – 1,000 Hz
Pretty much same conclusion as the notes above.
Front Block Hit 1 – 1,000 Hz
Pretty much same conclusion as the notes above.
Back Block Hit 1 – 1,500 Hz
This is the first test with a higher sampling rate. You can see a little more detail on the response curve.
Legacy Knock Sensor Hit 3 – 1,500 Hz
Both response curves had high peak values, but the WRX sensor appears to have a more gradual and smooth transient response.
WRX Knock Sensor Hit 4 – 1,500 Hz
Similar comments as above, the Legacy knock sensor curve looks “sloppier”.
Knock Sensor Spot Hit 1 – 1,500 Hz
Front Block Hit 2 – 1,500 Hz
Legacy Knock Sensor Hit 4 – 1,500 Hz
WRX Knock Sensor Hit 5 – 1,500 Hz
WRX Knock Sensor Hit 6 – 2,000 Hz
This is the first hit at a higher sampling rate. The curves show a similar trend as before with the WRX knock sensor curves being a little “cleaner”.
Front Block Hammer Dribble Hit 3 – 2,000 Hz
Front Block Hit 4 – 7,000 Hz
This is the first set of curves at a 7,000 Hz sampling rate. You get to really see the response curves in more detail. In these curves the scales are not the same, so you really can’t compare them together real well.
Legacy Knock Sensor Hit 5 – 7,000 Hz
As expected the Legacy response curve is much larger. The scales are the same.
WRX Knock Sensor Hit 7 – 7,000 Hz
Front Block Hit 5, Legacy Sensor Only – 14,000 Hz
In this test the sampling rate was cranked up to 14,000 Hz to get a very high resolution of the knock sensor response curve.
Legacy Knock Sensor Only Multi Hit 6 – 14,000 Hz
WRX Knock Sensor Only Multi Hit 8 – 14,000 Hz
There’s more symmetry in these response curves. That may be a result of the knock sensor or possibly the hit.
WRX Knock Sensor Multi Hit 9 – 7,000 Hz
These curves are back to a 7,000 Hz sampling rate. Again the Legacy curves look “sloppier” than the WRX curves.
Knock Sensor Spot Hit 2 – 7,000 Hz
Impreza Engine Idling with Legacy Knock Sensor 1 – 7,000 Hz
This curve shows the engine “noise” picked up by the Legacy knock sensor on my 1997 Impreza Outback Sport (EJ22) at idle ~ 750 rpm.
Impreza Engine Idling with Legacy Knock Sensor 2 – 7,000 Hz
Impreza Engine 1,000 rpm with Legacy Knock Sensor 1 – 7,000 Hz
Impreza Engine 3,000 rpm with Legacy Knock Sensor 1 – 7,000 Hz
Impreza Engine Idling with WRX Knock Sensor 1 – 7,000 Hz
Idling test for WRX knock sensor was conducted at the same rpm as Legacy knock sensor test.
Impreza Engine Idling with WRX Knock Sensor 2 – 7,000 Hz
Impreza Engine 1,000 rpm with WRX Knock Sensor 1 – 7,000 Hz
Impreza Engine 1,000 rpm with WRX Knock Sensor 2 – 7,000 Hz
Impreza Engine 3,000 rpm with WRX Knock Sensor 1 – 7,000 Hz
Impreza Engine 3,000 rpm with WRX Knock Sensor 2 – 7,000 Hz
All the curves can be viewed at this direct link if desired.
https://www.main.experiencetherave.com/ ... sensortest
. I love it (and secretly admit I'm jealous of your DAQ).
and it probably won't be the last. I was having a good ol' time with this. I need to read up on the DAQ software a little more. I litterally took the thing out of the box, installed the software and went to town.
