For all you forced induction guys.

[jdbubb at verizon.net (Dan Bubb)]

About a year ago I bought this little audio amplifier kit, a piezo crystal 
and a set of headphones to construct a DIY audio knock detector that I read 
about on www.autospeed.com.

Basically you glue the piezo crystal (converts vibration to a voltage output 
or converts a voltage input to vibration) to a clip that you can clip onto 
your engine block.

Well, I finally got off my dead ass and built the kit. The circuitry itself 
was nothing, the board is ~1.5" x 1" with 8 components. What took all the 
time was mounting all the bits in a box.

Finally tested it this weekend.

It really works. Mostly you just hear a lot of things clattering around in
there.
But, pinging/knock is a clearly detectable hard ticking sound.
So, as you're hauling ass down the highway despite lots of wind noise, lots
of road noise, lots of engine and exhaust noise, you can still clearly hear 
the
engine pinging.

Interestingly, after you shut off the engine from idle, you can also hear
the ball bearing turbo spooling down for 20 seconds or so!

Anyway, for about $50 and a few hours of assembly time this rates right up 
there
with a WB-O2 as a tuning tool to have for forced induction engines.

Dan