Placement of knock sensor
 

I'm installing a knock sensor for my FrankenCIS on steroids project. The engine is ready to go in, this is a last minute installation so I'm not removing the shroud and certainly not drilling/tapping heads for the 996 bridges.

I've looked at a few installations on here, and my preference is to mount it on the long stud for the throttle linkage that is on the case close to the base of the cylinders between #2 and #2 under the shroud. Proffighter and at least one other person have mounted it here. This will necessitate cutting a portion of the throttle linkage bracket that acts as a standoff moving 18mm to allow for the thickness of the knock sensor.

However I'm having trouble getting that stud out to allow me to insert the sensor without removing the shroud and all that entails. If I can't get it to budge I'm thinking of using one of the other studs for the throttle linkage. They are a few inches away, and not close to the cylinders.

What's the general consensus, will it make a difference?

I'm thinking not. If it's knocking the whole case should be ringing at 5,900 Hz.

Sure. Mine is bolted to the case under the shroud. But any solid mount to the case should be fine - Jake Raby makes a provision on the Type IV bellhousing and that works too.

IIRC, the MS guys advise not to mount too high on the head (to avoid valve train noise).

Bosch Technical Customer Information document Y 261 K23 E 03.11.1998 says:

Document also specifies that the sensitivity of the sensor may degrade up to -17% over lifetime.

Cheers Spug...

Interesting interesting comment about only the metal portion should touch the case, I need to verify that...

knock sensor
 

I have my Bosch knock sensor mounted at the back of the case by the oil chimney in a factory tapping... We had it on the dyno, and the sensor worked like a champ. ;-) couldn't be happier with the install...http://forums.pelicanparts.com/uploa...1547588202.JPG

I thought of mounting there. The aircooled VW guys seem to like a similar location for their engines.

Those two holes are smaller than the dia for the knock sensor, M6 or M8 vs M10 I think.

Did you drill out and re-tap?

I used the same spot and used one of these bolts.
https://www.mcmaster.com/92981a202

This is where mine is. M6X19mm if memory serves. Works great.

Slick, I like that - thanks for the link. Need some rotor button shims from those guys anyway - think I'll drop an extra buck 50 and re-locate mine while I've got the fan out...

Its a tight fit with that turbo oil line and the casting for the breather etc.

I had to loosen my oil line and bend it slightly and also filed a flat on the side of the knock sensor to have a mm or so clearance from the casting.

Still not sure if the plug will go on easily.

http://forums.pelicanparts.com/uploa...1547942261.jpg

This is how I mounted my pair of sensors, per factory 964 Carrera, using factory bridges (which are surprisingly cheap)....

http://forums.pelicanparts.com/9840019-post910.html

Of course, I needed to machine a flat mounting surface onto the underside of the bottom cooling fin on each head, but as the engine was stripped anyway, no big deal.

Monitoring each bank on the dyno a few weeks ago, and they were working fine.

I'm adding knock control to my MS2 and checked out this thread to get some location ideas for the knock sensor. The MS2 can only take one knock input. With that in mind, I wanted to mount the single sensor as central as possible and here is how I decided to do it. I removed the case stud and substituted a longer flange head bolt to secure the sensor and Locktited it in. An access hole was drilled in the shroud for the plug and that was it.

http://forums.pelicanparts.com/uploa...1554765560.jpg

http://forums.pelicanparts.com/uploa...1554765626.jpg

Bumping this thread since it contains some info pertinent to my situation.
Looking to mount sensor on base of throttle plate long stud, but the base on the sensor is a larger diameter than that recessed area on the case, around the stud. I thought to use a washer as a shim to get the sensor level, but one of the top posts says no washers to be used and only the sensor should contact the case only.

How to get around this?

I don't think this is correct as stock 964 Turbo knock sensor base is also smaller than sensor itself


http://forums.pelicanparts.com/uploa...1704716777.jpg

Mike,
I used a ground flat washer in this location to solve this problem.
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/1134450-j-s-knock-sensor-location.html#post11919474
Picture doesn't show the washer but it's there. My knock sensor came with a special bolt that has a rubber ring around the bolt, designed to keep the knock sensor from contacting the shank of the bolt. I cut a little short section of heat shrink and shrunk it around the shank of the throttle console stud it works the same keeps the knock sensor from touching shank of stud. I am sure it is going to work fine.
David
Performance EngiNerding

Hi David. Thanks for your post. Have you run your motor yet?

No, sad to say have not gotten it finished yet.
David

Slightly adjacent/off topic, but what sensors are any and all of you using and how did you select them? I read a while ago that the sensor will depend on the bore of the engine, but when I checked a specific Bosch sensor for fitment on various vehicles, the bores varied wildly. What then is the deciding factor?

This infographic has common part numbers. They differ mainly in the connector. I use the Mercedes one. Be aware that the Porsche air cooled one has a pigtail connector, which may or may not be useful to you.

As you can see in the infographic, the sensor itself produces the same output over a very wide range of frequencies. This is good and bad. It is good because you can use the same sensor for a wide range of applications. It is bad because you need to descriminate between the actual knocking frequency and all of the other frequencies present.

The knock frequency is roughly proportional to bore (temperature of combustion and cylinder pressure also play a role). For the bores we deal with (92 to 105) the basic knock frequency is 5.5 to 6.25 kHz.

Also attaching a screenshot from the shop manual that shows how the production aircooled bridge is actually attached.

http://forums.pelicanparts.com/uploa...1706184446.jpg

http://forums.pelicanparts.com/uploa...1706184940.jpg