Knock Sensor Location - EFI Conversion

[Speedy Squirrel]

Porsche exploited the natural frequency of a carefully designed mounting bracket for the knock sensor starting on the 964. By cleverly designing a bracket with a specific natural frequency, they could determine WHICH CYLINDER IS KNOCKING.

As you can see in this graph of cylinder pressure vs crank angle, knock occurs over a fairly small window of crank angle. With a knowledge of the engine position from the cam sensor, the knock signal can be corelated to a specific cylinder!



If your system is not capable of individual cylinder knock detection in a reliable way, the mounting bracket is of no use, so you would be better off mounting the sensor to the block. So there is that.

[Speedy Squirrel]

Originally Posted by mikedsilva

Interesting.
The reason I used an aluminium standoff/spacer is because the body of the sensor is larger than the relief that is around that particular stud. So this will result in an erroneous reading?

I think you would be in the trial and error zone with that arrangement. The aluminum standoff is probably pretty stiff and might be ok.

[JoeMag]

Interesting comment on "not" using the mounting bridge. My ecu (ol' motec M48), does not have knock capability, however, I have external "listening device" (need to look at what I have), and have the knock sensors on the two bridges going into the listening device.

Would I be better off to put the knock sensors directly on cyl 2 and 5's bosses that the bridge bolts on to?

[Speedy Squirrel]

Originally Posted by JoeMag

Interesting comment on "not" using the mounting bridge. My ecu (ol' motec M48), does not have knock capability, however, I have external "listening device" (need to look at what I have), and have the knock sensors on the two bridges going into the listening device.

Would I be better off to put the knock sensors directly on cyl 2 and 5's bosses that the bridge bolts on to?

IMHO you are probably fine as is for a listening device.