[Diy_efi] Re: Custom detonation detecting

[Eric Byrd]

> My understanding is that the resonant frequency of detonation is
> a function of bore diameter as the supersonic sound waves bounce
> back and forth, so a Cavalier knock sensor is probably tuned way
> off frequency.

How could this be?  Sound waves are not supersonic.  By definition they
are "sonic".  They travel at Mach 1, which is however quite higher than
in the atmosphere due to the heat and the pressure.  Second, how is the
resonant frequency relevant?  Peak pressure is on the order of 1300 psi
during combustion, and detonation causes a pressure wave at about 5000
psi, several degrees of crank angle after the normal pressure peak. 
Anything that will detect that kind of pressure jump will detect a
detonation, I would think.  Also, I would think the response speed would
be more important than the frequency the sensor is tuned to.

There are apparently complexities to knock sensor design that I am yet
unaware of.

Eric

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