DIY_EFI Digest V5 #718 - knock sensor

[Clare Snyder]

> Date: Tue, 28 Aug 2001 07:57:29 -0400
> From: Eric Fahlgren <efahl at adams.com>
> Subject: Re: Using a knock sensor from one engine on another
>
> TVS wrote:
> >
> > I assume the frequency has some dependence on variables
> > like bore diameter and combustion chamber shape, but is the knock detection
> > circuitry likely to 'listen' for a wide range of frequency's or just a
> > narrow band?
>
> I don't think bore has much bearing.  I've always thought that the
> bore was a single variable in the excitation function, but that the
> response frequency was determined by the structure (i.e., the block/head
> et al).  Imagine a 10 oz hammer ringing a bell whose principal mode is
> 100 Hz.  What do you hear?  Mostly 100 Hz.  Strike the same bell with a
> 10 lb sledge.  Still pretty much the same response.
>
> Here is some info (resonant frequencies of knock sensors) that will probably
> be of interest to you:
>
>    http://acc-electronics.com/cloud/images/page3_55.jpg
>
> Check the second and fourth columns of the table at the bottom.
> It looks to me like there isn't any correlation between the
> knock sensor's frequency and any of the obvious engine parameters
> like bore and stroke (but then again I didn't do any real analysis).
>
> - --
> Eric Fahlgren                            Mechanical Dynamics, Inc
> efahl at adams.com                          Ann Arbor, Michigan, USA
> - ----------------------------------------------------------------------------
likely just coincidence, but with the exception of the 4.9 liter engine there is
a pattern.
look at displacement per cyl.

5.8l = .725l/cyl - 5.4k
4.6l=.7125l/cyl - 5.7k
4.9l=.61l/cyl - 9.5k
3l=.5l/cyl - 6k
4.9l=.48l/cyl - 6.45k

The smaller the cyl displacement, the higher the frequency, except for the 4.9


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