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Recently there was an interesting discussion on the Guild of EFI tuners list regarding detonation and ways of sensing it. One person was adamant audio knock detection doesn't work (which we know isn't true) and made some references to measuring coolant and crankcase pressure as well.
How does this work? What data is gained from measuring these pressures?
#define Sarcasm = TRUE
After you melt a hole in your piston or cylinder wall, you'll see it as a rise in the crankcase or coolant pressure....
And after you've had a cylinder breach, I bet the knock detection isn't very effective if there is no longer enough compression to detonate.
To me it seems like those are very much "after the failure" sensing solutions. But I would be interested in hearing the reasoning provided.
Unless you use high speed (i.e. 10khz+) laboratory grade pressure sensors, that are gated to the combustion cycle, but have filtering to remove the noise generated on those channels from the normal operation of the engine, then you have no chance of detecting knock through the measurement of coolant and crankcase pressures. There is just too much latency in the signal to be able to do anything other than detect that the knock events have failed the engine in some manner.
You would be better off, and have more luck in detection, by mathematically analysing the crank rotation and look for a variance in the rotational speed of the crank being caused by the pressure pulse being generated by the knock event.