knock sensor location

I had a Allegro Gas Unit with a Chevy 8.1L..they were 2 located on each side of the engine block...very easy to get to and change out. Ordered them through Amazon, very inexpensive but make sure you get the wiring harness with it because that was my problem. Noise Sensors were OK but changed them anyway.
I was concerned at first on the info I received that they were located under the intake manifold which would put you spending more money if that is your case.
Hope this helps you!

If you are setting a knock sensor code be sure and check the wireing to the sensors, where it goes past the exaust manifold. On my 8.1it had gotten close to the manifold and burnt through the wire and was shorting out and setting a knock sensor code.

Under the Exaust manifolds, one on each side of the engine.

On my 8.1L it is on the driver's side, under the exhaust manifold and looks like this:

Not sure on the 8.1, guess I could look at mine. On the 7.4 they were in side of block, below exhaust manifold. Look for a can maybe 1.5" screwed into the block with wires attached.