[Diy_efi] Re: diy_efi Ignition Advance

[Robert W Hughes]

> I built up a little microphone amp circuit and glued a
> small condenser mic to a spring clamp. I plan on
> clamping it to the fin closest to the bottom of the
> piston skirt at TDC. Anybody care to describe what the
> onset of knock will sound like. 

I checked a knock sensor for an 86 Buick GN on a 2.8L engine and a 350. 
The sensor itself tested to be broadband, not tuned. The output at idle 
showed a low frequency component at the ignition speed (~60cps) and a 
pronounced peak in the 5-6kc region which is apparently the signal 
generated by the combustion event. I didn't have any way to force 
detonation, but I would expect the amplitude of this component to rise 
significantly in the presence of detonation. Used a Tektronix digital 
scope with FFT capabilities to make this measurement and it is not 
portable right now. Laptop with audio recording software and spectrum 
analysis  could probably do the same thing. There are a number of 
freeware real-time spectral analysis programs that might be able to show 
you what is happening.

-- 
Robert W. Hughes (Bob)
BackYard Engineering
29:40.237N, 95:28.726W or perhaps 30:55.265N, 95:20.590W
Houston, Texas "The city with too much Oxygen"
rwhughe at oplink.net
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