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Arvidw · Posted: Mon Dec 17, 2012 12:47 am Post subject: Engine knock detection

Today I installed a VW knock sensor on my 924. It is connected via the microphone port on my laptop to some headphones. The sensor is bolted to the cast iron engine block on one of the mounting points of the steel coolant return pipe. (the one closest to the center of the engine)

I find it quite amazing what sound you can hear without the engine running, a squeaking clutch lever, the shifter mechanism in the transmission, the thottle valve opening and closing, injectors firing in test mode. It really does give a very nice and clear sound.

However with the engine running the only thing I can hear is valve train noise, from 1000-6000rpm I can only hear the clattering of tappets and valves.

Has anybody got any experience with audible knock detection on a porsche 924 2.0? If so, what did you use, what did hear, up to which engine RPM where you able to hear engine knock?
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Porsche 924 2.0 Kompressor 136.1wHp @ 5650rpm / 201.9wNm @ 3900rpm (dyno @ dp-engineering.nl)

Carrera RSR · Joined: 08 Jan 2010 Posts: 2312 Location: Somerset, UK

Just bought myself a KS-4. The pro kit (which a mate has) allows you to listen in for knock whilst tuning. Once set the KS-4 will warn if knock starts http://www.phormula.co.uk/

Where did you bolt your sensor?
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

I've purchased but not yet installed a Knocksense (http://www.viatrack.ca/) after reading several posts on the topic.
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erstwhile owner of just about every 924 variant ever made

Fifty50Plus · Posted: Tue Dec 18, 2012 7:17 am Post subject:

OT:
Put a knock sensor on the Benz a couple years ago. Got it calibrated to the data AQ (not hooked up to control advance) and went out for a few laps. About 5 laps in, the engine threw a rod out of the block right where the knock sensor was mounted. Later the knock sensor data showed all normal until a massive spike and then flat lined.

Chuck
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1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

Arvidw · Posted: Tue Dec 18, 2012 7:24 am Post subject:

The sensor has been placed here:

@Carrera RSR, Have you already spend time tuning your 924 with the KS-4 Analyser? If so, how did you do that? Advance ignition and do a 2000-7000rpm run and listen for detonation, if not, advance even more?

@Ideola, Are you going to use the knocksense in combination with a EFI controller (Megasquirt?) or are you going to use the LED indication for tuning your engine?
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Porsche 924 2.0 Kompressor 136.1wHp @ 5650rpm / 201.9wNm @ 3900rpm (dyno @ dp-engineering.nl)

Carrera RSR · Joined: 08 Jan 2010 Posts: 2312 Location: Somerset, UK

My engine is still being built so no experience of tuning yet.

I was interested in the position of the sensor as that lug is an option but my fear its too low. The sensor needs to be as close to point of combustion as possible.
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Fifty50Plus · Posted: Tue Dec 18, 2012 9:32 am Post subject:

WEASEL149 · Joined: 19 Aug 2005 Posts: 595 Location: UK, Sheffield

A few others (Cedric?) have used the other lug between 3 and 4 which you can see near the crankcase breather in that photo. That's where mine is going.

When tuning, it's advisable to use electronic filtered detection and also listen on headphones/detcans. The human ear is a much more accurate 'device' provided you know what knock/detonation sounds like.
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1979 UK 932

Cedric · Joined: 27 Aug 2004 Posts: 2809 Location: Sweden

Carrera RSR · Joined: 08 Jan 2010 Posts: 2312 Location: Somerset, UK

Arvidw · Posted: Fri Dec 21, 2012 5:08 am Post subject:

@Weasel and Cedric, I'll try that point the next time. I have to fabricate some M10 to M8 bolt as my sensor only accepts M8. As it is probably a much better position it is worth the time and effort.

@Carrera RSR, that would indeed be a very nice spot to place the sensor. It is too bad it is so difficult to reach

I recorded the sound of my engine today. I tried to introduce engine knock by advancing the ignition drastically in only one load bin in my IGN table.

Video: http://youtu.be/rdEVSZz0n8E

I could really feel the engine struggling around 3300rpm however I can't really hear detonation around 3300rpm in the sound clip. However in the beginning of the clip just 2 seconds after opening the throttle I do hear some strange rattling noises so I'm wondering wetter that is detonation?
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Porsche 924 2.0 Kompressor 136.1wHp @ 5650rpm / 201.9wNm @ 3900rpm (dyno @ dp-engineering.nl)

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

You may find some useful info in this old thread Arvid:
http://www.924board.org/viewtopic.php?t=22379
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World`s quickest 924 2L slushbox

ksis · Joined: 22 Aug 2011 Posts: 120 Location: New York

I thought a knock sensor should be placed on number one piston at the middle of the stroke. Check the placement of a sensor on a MK2 VW 1.8.
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Carrera RSR · Joined: 08 Jan 2010 Posts: 2312 Location: Somerset, UK