Ignition retard knock sensor.

[d houlton x0710]

G. Scott Ponton wrote:
> 
> pre-ignition or any ignition for that matter. The reason you can "ease" into
> the throttle an let the boost climb slowly has to do with the density of the
> air charge. It works the same way with a NA engine which likes to "ping" at
> WOT. If you slowly step into it you reduce the density of the air charge and
> by the time you get to the higher revs the "time" it takes for the piston to
> move is reduced. Therefor, even though the cylinder pressures are "equal",
> the uncontrolled burn doesn't have time to create "ping" like it does at
> slower engine speeds.
>     When you open the throttle suddenly to WOT you are imposing no
> restriction to the density of the air entering the cylinders. Boost won't
> necessarily climb quickly as it takes some time for the turbo to "spool up".

Makes sense I guess.  I really didn't know why it is happening (or how to 
prevent it), just that it does.


> <snip>
> 
> >It seems that unless you can factor in rpm (at the very least) in addition
> >to boost to more accurately predict knock, you have to *really* retard
> >ignition to cover the worst case, which makes you suffer a power loss most
> >of the time.  That's why I figured the active J & S system would be much
> >better.
> 
>     Here you are nearly entirely correct. One other thing you are missing or

Hmm, now that I think about it, although boost and rpm would be more 
accurate for predicting knock, I just explained that at a certain point,
knock was directly related to the gas pedal once boost and rpm stabalized.
You explained this because when you go to WOT, boost and rpm don't change
instantly, but air density does.  So, since air density is measured by the
MAF and appears to be working correctly because the A/F meter isn't 
dropping off lean, maybe then monitoring boost, rpm and injector pulse
width (or duty cycle, or maybe the MAF signal directly) could pretty 
accurately predict knock?  

It would take trial and error I'm sure to tune such a system, but it seems
it would be relatively easy to do just by running a few tests.  Maybe use
boost and rpm to set a baseline retard and then use the injector pulse 
width / duty cycle / MAF output (or maybe even throttle position?) to set 
the gain to add more retard as necessary?

If I were to come up with a box that could monitor these 3 things and come
up with an output (say a 0 - 5 volt signal for instance), any ideas on how
to make the ignition retard accordingly?  Do the MSD prducts happen to
have any kind of external inputs that could be used to retard ignition?

They make a stand alone retard system with a dash mounted dial.  If this
dial is just a pot (seems likely) maybe I could use that, snip the dial
off and feed an appropriate signal from my little black box?



> forgetting though. Once pre-ignition has started, you have to retard the
> timing further to get rid of it than you would have if you prevented it in
> the first place. IMHO the best way to handle this is to figure out how much

Yes, I have noticed this too.  If it starts detonatiing at say 6 psi, I
have to back all the way down to like 2 or 3 before it stops, but I can
go right back up to 5 (all within a span of a second or so) without it 
happening again.


> 
>     I mentioned once before in another post I had added a ignition retard
> device to one of my old Pontiacs. I finally have dug up the notes on it.
> This may be a "cheap" alternative for many. The unit I used was not and ECM.
> It is an ESC controller off a 82 Chevy P/U. This was a standalone system
> that worked with the normal dissy and uses a Knock sensor with a board to
> retard the timing until knock goes away. It is fairly easy to connect and
> doesn't require much besides the sensor and the proper ignition module. I
> forgot to bring the part #s home with me. If any are interested I can scan
> the skitz and include the part #s I used. I had to manufacture a dissy for
> my Pontiac as I was using a Tripower intake and a normal HEI won't fit
> behind it. You should be able to hook it into your current ignition system
> as the negative of the coil goes out to the module and as long as there is
> no "knock" signal it just comes back. Otherwise it "delays" it until the
> knock signal goes away.

Yes, please could you send this on to me or post to the ftp site?  I'm
afraid my knowledge of the ignition system is a bit limited.  What do you 
mean by connecting it to the neg side of the coil and it either "just comes
back" or "it delays it"?  Is this like grounding the neg side instantly or
waiting an instant to ground it or something?  Is controlling the ground
of the coil how you would retard ignition?


thanks
--Dan
houlster at inficad.com
http://www.inficad.com/~houlster/amigo.htm