I've tried to find one on the web but came up empty. Does anyone of you know of a formula that will calculate the fundamental frequency of the knock signal based on boresize (and maybe something else)?
I want to build a knock monitor based on a tuned filter, but we don't have an engine on the dyno at the moment and I don't wish to pay Cosworth the big bucks to cough up the numbers.

Igor

Knock frequency is actually pretty easy. Take a stab at speed of sound at the in-cylinder densities when knock occurrs (ie near peak cylinder pressure). The frequency will be the number of times that sound wave bounces back and forth across the bore (ie 1 cycle is twice bore).

For reference a 77mm bore is like 14 kHz. However, this only works for in-cylinder pressure transducers. Your block will resonate at a different frequency (usually quite a bit lower) if you intend to use a knock sensor. And that is so complicated it is usually determined experimentally.

Thanks John,
Interesting that what you measure on the inside doesn't match what you hear on the outside. You learn something new here everyday.
Well, I guess I'll just slap on a scope when we've got something on the dyno.
If you see clouds of smoke coming out of the Spyker at Le Mans next year, you'll know it didn work :-)

Igor