Fun with knock sensors (Legacy vs. WRX Comparison)

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Legacy777
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Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

I have, and still am contemplating swapping over to a WRX knock sensor to run on my Link from the stock Legacy knock sensor. I was not sure what differences there may be. I remember reading this post from BSOD2600 with some info from BigMoose about different knock sensors.

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.

http://www.main.experiencetherave.com/s ... 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
Image


Legacy Knock Sensor Hit 2 – 1,000 Hz
Image


WRX Knock Sensor Hit 1 – 1,000 Hz
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WRX Knock Sensor Hit 2 – 1,000 Hz
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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.
Image


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.
Image


Block Multi Hit 2 (2nd location) – 1,000 Hz
Pretty much same conclusion as the notes above.
Image


Front Block Hit 1 – 1,000 Hz
Pretty much same conclusion as the notes above.
Image


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.
Image


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.
Image


WRX Knock Sensor Hit 4 – 1,500 Hz
Similar comments as above, the Legacy knock sensor curve looks “sloppier”.
Image


Knock Sensor Spot Hit 1 – 1,500 Hz
Image


Front Block Hit 2 – 1,500 Hz
Image


Legacy Knock Sensor Hit 4 – 1,500 Hz
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WRX Knock Sensor Hit 5 – 1,500 Hz
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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”.
Image


Front Block Hammer Dribble Hit 3 – 2,000 Hz
Image


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.
Image


Legacy Knock Sensor Hit 5 – 7,000 Hz
As expected the Legacy response curve is much larger. The scales are the same.
Image


WRX Knock Sensor Hit 7 – 7,000 Hz
Image


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.
Image


Legacy Knock Sensor Only Multi Hit 6 – 14,000 Hz
Image


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.
Image


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.
Image


Knock Sensor Spot Hit 2 – 7,000 Hz
Image


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.
Image


Impreza Engine Idling with Legacy Knock Sensor 2 – 7,000 Hz
Image


Impreza Engine 1,000 rpm with Legacy Knock Sensor 1 – 7,000 Hz
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Impreza Engine 3,000 rpm with Legacy Knock Sensor 1 – 7,000 Hz
Image


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.
Image


Impreza Engine Idling with WRX Knock Sensor 2 – 7,000 Hz
Image


Impreza Engine 1,000 rpm with WRX Knock Sensor 1 – 7,000 Hz
Image


Impreza Engine 1,000 rpm with WRX Knock Sensor 2 – 7,000 Hz
Image


Impreza Engine 3,000 rpm with WRX Knock Sensor 1 – 7,000 Hz
Image


Impreza Engine 3,000 rpm with WRX Knock Sensor 2 – 7,000 Hz
Image


All the curves can be viewed at this direct link if desired.
http://www.main.experiencetherave.com/s ... sensortest
Josh

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skid542
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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by skid542 »

You're such a geek Josh! :-D. I love it (and secretly admit I'm jealous of your DAQ).


Interesting results too. Have you tried other sensors for the different models? I.e. is the trend you're seeing between Legacy vs WRX limited to only two data points or is there strong evidence that the sensor design has inherent response differences?
Lee

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by 93forestpearl »

Damn, someone got a little carried away with making neat graphs, lol.




Interesting work. What do you think you'll use in the end?
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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

Yes I know....I've been told I'm a geek/dork before :lol: 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.

I've only tried those two sensors. I got a recommendation from the shop that did my tuning about the values they were seeing from my knock sensor vs. what they typically see from the WRX knock sensors. The problem is I have no standard or calibrated way to test the sensors like what Big moose was doing. I was simply just graphing their response curves and trying to make assumptions from them. The other thing too....because the sensors are in different locations, it's more difficult to compare apples to apples. A test jig or something would help. If I got a hold of some different sensors, I'm sure I could try doing some more testing.
Josh

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

Dan,

Yes I did get a little carried away with the graphs...hahaha. This was one of those posts I wrote up in word and then pasted to the bbs.

I am probably going to try the WRX sensor and see how it works with the link. I also may try and tie in the data acquisition software to the knock sensor output to see if I can correlate a certain knock value on the Link with a response curve.

Ultimately, I'll probably need some form of head phones or something similar to listen for knock to set the thresh hold. If Link doesn't update their firmware to provide closed loop knock control, I may decide to use something else for knock control....which would kind of erk me, but I would like to have it to safe guard the motor.

I'll keep ya posted on what I decide to do.
Josh

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by 93forestpearl »

On my motor, knock was audible at around 80-100 on the Link with a 22T knock sensor, even though the scale goes over 1000.
→Dan

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

What did you use to listen for audiable knock?
Josh

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by 93forestpearl »

My ears and the windows open.



tick tick tick....and the link read above its normal max of 15....
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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

Ahh ok.....didn't know if you had a set of earphones hooked up to a knock sensor or something to set a baseline.

The G4 is better I think at setting up the knock detection and can do individual cylinder knock detection, which is a plus....but like I mentioned it only retards timing when the PC Link is hooked up.
Josh

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by n2x4 »

VERY interesting data. Here all along I always thought that the knock sensor was the same internally between all revisions. Apparently I'm wrong.

How are these sensors hooked up - what connector are you using?
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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

You can kind of see in this picture.
http://www.main.experiencetherave.com/s ... G_1842.JPG

The WRX one had the connector torn off, so it was directly connected to the DAQ box. The Legacy one I made a jumper wire with connector that slid onto the existing connector for the Legacy sensor.
Josh

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

Just a quick update, the actual pins on the knock sensors are slightly different, but they are close enough where you can swap the actual connector. So you can run a WRX knock sensor without having to really do any re-wiring. The pin is slighly longer and the rubber seal sticks out a little bit, but that's it. When I get the car running again, we'll see how the Link likes the new sensor.

Here's a couple pics:

Image
Image
Image
Image
Image
Image
Josh

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by kimokalihi »

Oh man, I wish i had realized you could swap the connectors. I'm pretty sure I accidentally bought the WRX style one a year ago and saw it had the wrong connector and bought the legacy one afterwards thinking I wasn't going to be able to use it. I'm pretty sure I still have the unused WRX one sitting in my garage.
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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

The new WRX connector has a little plastic piece you have to pull forwards so you can get a small screwdriver in there to bend the tab down so the pin will come out. Took me a little bit to figure out. It's a different color plastic than the surrounding connector.
Josh

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by cj91legss »

Got a part number for the wrx knock sensor?
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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

I'll have to get it off the box when I get home and post it.
Josh

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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by cj91legss »

that'd be awesome, i'll try to find it online as well... im thinking i may just order one, mine has a crack on top and it's not showing a code but you never know....

edit, here's the number 22060AA100
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Re: Fun with knock sensors (Legacy vs. WRX Comparison)

Post by Legacy777 »

Yup, that's the number of the knock sensor I used.

The knock sensors on the 2006 and knewer are a little different, so yeah use the 22060AA100 sensor.
Josh

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