modify aluminum case for knock sensor?

jpnovak · 02-14-2008, 08:33 AM

I have a question about adding a knock sensor to my upcoming build project. My EFI has the ability to retard timing when combined with a knock sensor. To me this is important as 100+ degree TX summers at the track make me worry about detonation.

The problem is that I don't have a boss to attach one. Previous threads in the archives mention the cylinder base/case area to mount a knock sensor. We can also reference the 3.6 cylinders that have a "connecting" bar across the cylinders for a knock sensor.

Most knock sensors just mount on a M8 stud or bolt but need to be firmly attached to the surface for optimal frequency transduction.

My 3.0 has neither the ability to mount a sensor on the cylinder bases or case. I have an idea to drill and tap the aluminum case above Cylinder 2 and 5. I was thinking I could drill and tap a small hole not all the way through directly above the case bolt at the base of the cylinder spigot. This point has case webs and crank main bearing webs coming together for strength and there should be plenty of material available to drill a 1cm deep hole for an M8 stud.

What do you think?

tctnd · 02-14-2008, 09:00 AM

In general air cooled engines are not considered good candidates for knock sensors. The are essentially microphones and cannot easily differentiate "knock"or "ping" from all the other noise present. Liquid cooled engines damp most of the noise out. Hopr this helps.
Phil

TimT · 02-14-2008, 09:42 AM

You can mount it on one of the three studs which are used to mount the throttle linkage plate. Pull one of the studs, and install a longer stud to account for the thickness of the knock sensor.

911quest · 10:01 AM

Quote:

Originally Posted by TimT

You can mount it on one of the three studs which are used to mount the throttle linkage plate. Pull one of the studs, and install a longer stud to account for the thickness of the knock sensor.

The aluminum cases don't use this mount.....most new porsche, subaru boxer motors have it mounted on the case.

The only thing I see a proble with is the way they mount they usually don't mount flush on the case they seem to set 10-15mm of of the case on there own boss I would think there is a reason for this possbly to cut down on vibration that could throw off the sensor

Bill Verburg · Bill Verburg's Garage

964 and 993 mount on the cylinders

jpnovak · 02-14-2008, 04:43 PM

Thanks Tim. I totally forgot about those bosses. I have been running carbs and EFI on the 3.0 so long that I forgot about the CIS linkage boss.

JohnJL · 02-14-2008, 07:33 PM

I had my cylinders tapped and use 993-style bridges as above. I know of a supercharged 3.0 locally which successfully uses a knock sensor tapped into the case underneath the breather plate. I dont have pics but you can check www.supercharged911.com for more info.

safe · safe's Garage

Quote:

Originally Posted by jpnovak

My EFI has the ability to retard timing when combined with a knock sensor.

What EFI system will you use?

jpnovak · 02-16-2008, 05:41 AM

I am using a Megasquirt system. Here is my build. I am about to assemble a new engine due to a broken head stud. I am just planning for the "while you are in there's".

EFI Kicks A$$ - the ST goes electric

hcoles · 02-16-2008, 09:06 AM

One would hope that the Megasquirt people could tell you how easy it is for the system to recognize knock on different engines and where the likely best places are to pick up the signal they are looking for. I haven't read too much about this but I expect there is some frequency range that pops up when knock happens. The question is... on your engine is the frequency or frequency range matching what the system is looking for. Of course the Porsche factory engineers can easily find what this is for a given engine... for DIY's maybe not so easy.