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!

http://forums.pelicanparts.com/uploa...1704856804.jpg

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.

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.

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.