I found the following paragraph at this site, http://www.sdsefi.com/aircraft.html.<br><br>11/20/00 Knock Sensors on Aircraft<br><br>We don't recommend the use of knock sensors for engines powering aircraft. Generally speaking, air cooled engine have too much mechanical noise to be able to filter it out to hear the knocking. The second problem on opposed engines especially, is placement of the sensor. Most auto manufacturers spend countless hours determining optimum placement. You probably can't. The third concern is that the engine needs to actually knock before the ECU retards the timing which isn't good for it. Fourth, if you have the sensitivity set wrong, the ECU may retard the timing the full 25 degrees because of mechanical noise. You would lose over 50% power and this could cause an accident. Extremely high EGTs could also damage the engine. Finally, if you are running on 100LL and have reasonable manifold pressure limits, compression ratio and ignition timing, the engine WILL NOT knock in the first place. <br><br><br>I am installing a 2.5 in a fixed wing and am trying to decide if I want to use the knock sensor or O2 sensors, (2.5 uses two O2 sensors). I am inclined to by-pass them. I would be interested if anyone else has not used them and what were the results.