(Knock detection methods) Re: Maximum advance

[Shannen Durphey]

The knock sensor is a microphone with 2 connections.  One is the wire connected
to the end, the other is ground.  I use a microphone jack and cable and connect
the two wires from the cable to the ks ground and the "regular" ks connection.  

I do not connect the ecm to the ks when doing this.  I have used a separate ks
just for this monitoring.

Shannen

dom wrote:
> 
> How would one go about hooking the knock sensor up to an amplifier?
> -Dom
> 
> on 7/12/01 7:22 PM, Shannen Durphey at shannen at grolen.com wrote:
> 
> > Axel Rietschin wrote:
> >
> >>
> >> With a copper pipe bolted on the head and connected to a "stethoscope" on
> >> the other end, across a fully soundproof wall, you will hear even isolated,
> >> spurious knock bursts and be able to back off timing very quickly. For this
> >> process to work well you need to stabilize the engine at every load/rpm
> >> points and adjust them individually, and you need silence and concentration.
> >
> > As you mention further in the post, a knock sensor connected to an amplifier
> > and
> > a good set of headphones will reveal huge amounts of engine noise, knock
> > included.  It's a good experience, IMO, for every average tuner to drive
> > around
> > and listen to one of these babies.  Even if you're not chasing knock, it's
> > good
> > to listen to what the knock sensor normally hears.  For the guys that like to
> > set timing almost at knock, it's a great experience.
> >
> > Shannen
> >
> >>
> >> Knock is very random in nature and you may only have one burst of 10 or 15
> >> out of 200 or 300 burns that pings, I'm not sure how you'll catch and
> >> display that in real time with a PC, but your ears definitely will, every
> >> time, provided you are in a silent environment.
> > In a car and with good headphones you'll hear a fair amount of noise also.
> >
> >>
> >> When advancing timing small steps at a time you will feel an ever so subtle
> >> change in the absolutely chaotic internal engine noise that will tell you
> >> knock is just about to show his ugly face and soon thereafter you'll hear an
> >> erratic burst of noises somewhat similar to what you hear when you lit a
> >> match, only much shorter, slightly standing out of the huge background
> >> noise. When you hear that, quickly back off 2-3 degrees and you are done
> >> with that map point. If you back off timing but still hear more matches
> >> lighting up, reach that big red pushbutton (the one saying "emergency stop")
> >> as fast as you can but chances are it is already too late.
> >>
> >> When I mapped my engine we were up to three in the booth, the person driving
> >> the dyno, myself on the laptop and the third person with his hand on the red
> >> button. We had one expensive piezo sensor connected to an oscilloscope
> >> (useless), one standard Bosch knock sensor connected to a Nagra tape
> >> recorder with me on the headphones and the copper pipe for the dyno
> >> operator; the only words allowed were "OK" to move to the next rpm site and
> >> "Stop" to back off immediately.
> >>
> >> We spent about 5 minutes on every row on the map including maximum load,
> >> releasing the brake in small steps to stabilize the engine at every rpm
> >> sites on the current row; it took me about 10-12 seconds per site to reach
> >> the premise of knock and back off two degrees or so; we let the engine idle
> >> at 3000 rpm for 2-3 minutes between rows to allow the turbo to cool down
> >> from bright yellow to dark red; the ECU was taking care of the mixture
> >> details using its own NTK sensor, precisely tracking the target lambda set
> >> in the appropriate map (we did a rough fuel map before using a very
> >> conservative ignition map).
> >>
> >> The whole process took several hours and take my word for it, it takes a lot
> >> of nerves to play with the knock limit at high load for 5 minutes flat at a
> >> time with the whole exhaust header and turbo yellow-white, with up to 1100C
> >> on the temp dial toward the end of the rpm range. The ECU was connected to
> >> all the usual engine sensors and we had additional sensors for almost
> >> everything, pre and post intercooler temp, per cylinder exhaust temp, oil
> >> pressure, fuel pressure, oil and water temp in and out of the engine, oil,
> >> water and fuel flow, manifold pressure, crankcase pressure and another WB
> >> O2 - nearly 20 extra sensors  - with computer controlled normal range, alarm
> >> and emergency stop values for every of them (the dyno would shut down
> >> automatically if one of the value went out of the allowed range) - I
> >> describe all this just to emphasize you can't really do a proper ignition
> >> mapping job on a chassis dyno, much less on the road, and that you need more
> >> than a plug sensor, no matter how good, to do it right.
> >>
> >> Also I don't want to discourage anyone, but the only ECUs I know that are
> >> capable of using those pressure sensors for closed loop ignition are using a
> >> dedicated DSP chip just to process the sensor's signal, and they _are_ the
> >> ECUs, I mean they already knows where the crank is and when they fired the
> >> cylinder they are monitoring. I believe the signal is extremely noisy and
> >> somewhat hard to interpret properly in real time. The software has so many
> >> adjustable parameters in the knock strategy section it makes me wonder how
> >> long it takes to adapt it effectively to a particular engine. Note that I'm
> >> not against progress (I believe I was the first to post references to the
> >> NTK/NGK spark plug sensors here a while ago) it is also well known that Saab
> >> and others pioneered innovative ways of sensing knock but for most of us,
> >> the old way is still by far the best IMHO.
> >>
> >> --Axel
> >>
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