Probably a case of locking the door after the horse has bolted but I wanted to at least try to detect knocking this time. I looked at some very expensive sensors and some cheap ones. The difference seems to be the ability to sort out knock from all the other noise in an engine. I resoned that the human ear isn't bad so went with the school of "detonation cans" which are basically ways to listen to the detonation. I bought this personal listening device from Radioshack, removed the microphones and epoxied them to some clamps. hopefully I will be able to find a good spot to listen in on the combustion..
For an Idea on how it should sound try www.theknockbox.cc