[Diy_efi] Re: Crank sensor for knock detection?

[Marcell Gal]

Hi Mike, 

> the question was supposed to be was it possible
> to use the crank sensor to detect detonation in an engine...

I think not.
What do you expect the crank pulses to do?
Let's say we have 60-1 impulses per rotation.
We can calculate delta-omega / dt,
which might fall back at knock (knock loads the bearings but
does not produce as much power as right timed burning)
but I would not try to calculate from that.
Perhaps if we knew the exact load, but unfortunately
we don't  (because it depends on millions of factors:
hills, clutch, gear, road surface ... ). Even if you could
come up with something it would be far worse than the
cheapest knock sensor. Investing your energy in ion
sensing would benefit thousand times more. 

> Is it possible, and is it done on production engines that don't come
> with knock sensors?

I doubt it's done in production. 

I think today many engines have knock sensors,
even normally aspirated ones (at least mine has).
It can detect bad quality gas, carbon deposits in the
cylinder and maybe other anomalies. 

Marcell

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