What is a knock sensor

I'm told when swapping a 305 to 350 i need to change the knock sensor. Does this mean put the 305 knock sensor on the 350? Also where is the knock sensor.

I would not have thought you would have to change it but, oh well. It sounds like you need a knock sensor from a 350 because the one from the 305 won't work. They bolt into the side of the block towards to front. Mine is in the block by the starter. You will see a wire that plugs into a round thing that is threaded into the block. What these do is they detect noise, so if the timing is off or you have any fuel issues or anything that wouls cause your engine to spark knock, they tell the computer to retard the timing until the spark knock goes away.

~bingo~