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Knock Tech: pre-ignition vs. detonation

Posted by turboglenn, May 18, 2008
Tuning & Engine Management - 4G63 EPROMS, ECU, MAF, knock, EGT, wideband, datalogging, fuel trims, etc. Read this Forum's Strict Guidelines.

  1. turboglenn

    turboglenn Proven Member

    Joined:
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    Thought some of you would be interested in this, to make it easier to read and follow, i will cut and past the intro and then Link to the 8 page in depth article by another guy
    on the 2nd post is articles about building your own stand alone kncok sensing and timing retard system from GM parts
    In this copy and pasted part is a very simple breakdown that a lot of people that are newer to tuning or just don't really understand detoantion can really use so look at it closely at least.



    Background

    Engine Knock-that annoying rattling sound that sometimes comes from under the hood of your pride and joy, is a killer. We have all heard the stories of blown head gaskets and broken pistons. Maybe it has already happened to you, too. But just what is knock, sometimes also referred to as detonation?

    The knocking sounds you hear are the cylinder walls set into oscillation by intense pressure waves, caused by abnormal combustion. Normal combustion is a controlled burn that starts from the spark plug and spreads outward, causing a pressure rise in the combustion chamber. This pressure is then converted into torque on the crankshaft. Ideally, the peak pressures will occur about ten to fifteen degrees after top dead center (TDC), as the piston is on its way down.

    Detonation is a form of abnormal combustion that starts off right, but at the last millisecond, something goes wrong. The remaining air-fuel mixture, called the "end gas", explodes all at once, instead of burning in a controlled way. Resultant engine damage is caused by an instantaneous pressure rise that can excede 1500 psi. This is more than double the normal peak combustion pressure, and will blow head gaskets, break piston ring lands and hammer the rod bearings. Another form of damage seen is that the tops of the pistons will be eroded and can even melt.

    High octane fuels are resistant to detonation because they contain compounds that slow down the chemical chain reaction we call combustion. If left unchecked, these chain reactions would quickly escalate, resulting in increasing damage to the piston and other engine components. All fuels, regardless of octane, have a knock limit. This is reached when the temperature of the "end gas" reaches an autoignition point. Combustion chamber designers use high swirl inlets and large "quench areas" to fight this "autoignition" problem. There are other factors beyond these mechanical design features which influence "end gas" temperatures. Some of these are: (1) Intake charge temperature, (2) Coolant temperature, (3) Compression Ratio, (4) Boost pressure, (5) Spark timing, (6) Air-fuel ratio, and (6) Humidity.

    An increase in compression ratio, boost pressure, or spark timing will increase peak cylinder pressure, which in turn raises the "end gas" temperature. Higher inlet and coolant temperatures also increase the "end gas" temperature. Richer mixtures can be used to cool the charge. At some point beyond about 10:1, however, will again increase the tendency to detonate. A decrease in humidity will also tend to increase detonation.

    Solutions

    Some things you can change, and some you are stuck with. Obvious things to do are get cold, fresh air to your air cleaner, use the best form of charge cooling (intercoolers) you can afford, and work on your cooling system to bring the temperatures down. Get an Air-fuel meter (O2 meter), and if necessary, install a fuel enrichment device. For turbo/supercharged engines water-alcohol injection can be very effective, but the volumes required mean constant refilling and maintenance, so in the long term it is a specialized solution that has a lot of drawbacks.

    Spark retard, within limits is the most powerful means of controlling detonation. Traditionally, this has been a manual affair by simply cranking the distributor back "x" degrees, Some electronic devices can retard timing in relation to manifold or boost pressure and other devices offer simple manual knobs you can alter the timing with if an audible "ping" is heard. Many newer cars are quipped with knock sensors that retard the timing when detonation occurs. This form of closed loop spark control where the vehicle's ecu automatically retards all cylinders when detonation occurs, a situation we call "retard all". On a select few modern engine controllers (Porsche, Corvette) the microprocessor is programmed to retard individual cylinders as knock or detonation occurs. The problem with either of these approaches is twofold: First, the OEM carefully maps a complex set of spark curves and only allows a small degree of retard to take place, typically 4 degrees; Secondly, these ecus are highly specific and are not readily adaptable or programmable for other applications.

    J&S SafeGuard versus the Detonation Dragon

    J&S Electronics has developed the SafeGuard which uses a knock sensor to provide feedback to it's microprocessor which, in turn, controls the timing for each cylinder on an individual, optimized basis. Firms like DINAN Enginneering, Kenne Bell, and CarTech have successfully used SafeGuards in their installations. DINAN used SafeGuards in their high dollar integrated BMW turbo kits which set very high standards for performance and sophistication. Kenne Bell has used SafeGuards in Syclone and Typhoon V-6 turbos for years to complete a very successful upgrade program for these General Motors vehicles. CarTech Stage III Mustangs completed hundreds of runs at the dragstrip running 12 pounds of boost with times in the low 12's and high 11's. In the last few years supercharged Mazda Miatas have become the rage, but owners have found out that killing the stock timing was not the way to horsepower heaven. By adding a J&S SafeGuard and returning timing to factory specs the missing low end performance and extra horsepower were rediscovered.

    J&S Electronics has more than a decade of experience in wrestling with the thorny issues that surround knock-sensing and detonation. It is not a simple matter of hanging a microphone on the engine and listening for the tell-tale "knock". If you have discussions with OEM powertrain engineers they can tell you of the difficulties they face in the areas of signal discrimination or "noise" as well as the issues related to how the actual control over the timing should be done. J&S's SafeGuard has sophisticated mathematical controls or algorithms than discriminate between noise and actual "knock", and has user adjustable controls that allow for sensitivity as well as amount and speed of retard. Whereas OE retard schemes are limited to say 4 degrees, the J&S SafeGurad can be set for up to 20 degrees of ignition retard. This prevents catastrophic failure than can occur should you loose engine coolant or some other unforseen event. The J&S SafeGuard will control the timing of each cylinder in proportion to the degree of detonation occuring, thus maximizing performance and preventing engine damage.

    Detonation is the precursor to preignition and only J&S Electronics can provide you a real-time solution to your ignition timing that both maximizes performance and protects your investment.






    Preignition and detonation are two separate and distinct events. It was first pointed out as far back as 1906 that the two phenomena were not only quite distinct but were in fact not related to each other. In the first place, preignition in itself does not produce an audible "knock" and if it is audible at all it could be described as a "dull thud". Because preignition is frequently brought about as a result of persistent detonation, the distinct "knock or ping" of the latter came quite erroneously to be associated with it.

    It is by no means uncommon for preignition, or in this case it would be more correct to describe it as autoignition, to occur at the same phase as the timed spark. In this case the ignition can be switched off, and the engine could continue to run perfectly steadily without the slightest observable change in performance, sound, or any other characteristic. The danger, however, lies in the fact that all control of timing can be lost and ignition may creep in earlier in the cycle.

    The danger of preignition lies not so much in the development of high pressures but rather in the very great increase in heat flow to the piston and cylinder walls when the ignition occurs too early in the cycle. This increase in heat flow, in turn, raises still further the temperature of the hot spot or surface which is causing the preignition resulting in even earlier ignition. At some point the temperatures are elevated to the point where the incoming charge is ignited, causing backfiring in the inlet tract. The belief, still widely held, that preignition can give rise to dangerously high cylinder pressures is totally false. Under no circumstances is the peak pressure resulting from preignition appreciably higher than from a spark-initiated ignition and, in both cases, the peak is reached when the maximum pressure is attained at or just after top dead center, that is to say, about 10 degrees earlier than the normal optimum. As the time of ignition is further advanced by either advancing the time of the spark or by earlier preignition, the maximum cylinder pressure falls again due to the excessive heat loss, for the piston is then compressing gas at or about its maximum temperature, and the intensity of heat flow is increased many times. The danger lies not in the production of excessive pressures but of excessive heat fow. The intense heat flow in the affected cylinder can result in piston seizure followed by the breaking-up of the piston with catastrophic results to the whole engine.

    In nine cases out of ten, preignition is initiated by overheating of the sparkplug electrodes or some sharp point or edge that has gone "critical". We are accustomed these days to focus all our attention on the subject of detonation for it is the limiting factor controlling the performance of a spark-ignition engine. We are apt to forget that the real danger is that it leads on to preignition. In itself, detonation is not dangerous... It is the preignition it gives rise to that can so easily wreck an engine. J&S Electronics SafeGuard is your best defense against detonation and the harmful effects it can lead to.

    8 Page article on knock, PCP, detonation and every other aspect that's related

    And incase you've heard me rave about the J&S in my car. There website is where this info originates from, there's also a lot of end user feedback found on forums all over linked here as well. J&S user feedback on knock control
    #1
  2. turboglenn

    turboglenn Proven Member

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    Omaha, Nebraska
    There's also an article on this page linked that tells of making your own stand alone knock sensing and timing retarding module from odlder GM motors parts...VERY COOL INFO!!!
    here ya go, build your own knock sensor system
    From: jgd (John De Armond)
    X-Source: The Hotrod Mailing list
    Date: Apr 1992
    Subject: Knock sensors

    >> I have learned some things about the MSD 8972 that may be of interest
    >> to this group.

    >I have been thinking about purchasing the MSD 6A setup for our
    >motor...

    Get the -6T or the one with the rev limiter built in (6L?) The-6T
    comes with a very nice rubber vibration isolation kit for mounting.

    >does the above work along with the 6A?

    Yes.

    >what would be involved in
    >installing a knock sensor into an engine not originally equipped with
    >one? what does the knock sensor do? How does it work?

    I posted a monologue on knock sensors a couple of weeks ago. Part is
    included below. Physically installing the sensor is no problem - just
    find a good solid point on the head or block, drill a hole if one does
    not already exist, tap and screw the thing in. Getting it to work with
    the ignition is another trick alltogether.

    I've bought several so-called knock controllers over the years. None
    worked. They all responded to the gross signal from the knock sensor
    which meant they are always actuated at high RPM. For it to work, the
    controller MUST gate the knock signal to crank position. You have basically
    four choices.

    1. Certain GM vehicles used an external knock controller that interfaces
    with a special HEI unit. I believe it could be adapted to any system.
    A note describing the system set to me by a friend is enclosed below.

    2. The SafeGuard system by J & S electronics. This is a digital aftermarket
    system that supposedly controls knock on a cylinder-by-cylinder basis.
    I've not used the system but I looks OK. Expensive at about $425.

    3. The Electromtive direct ignition system. This system uses a crank
    trigger, direct ignition (no distributor), is PC programmable and
    listens to a knock sensor. The system has gotten some bad press on
    the net but my experience is that it works as advertised. Mounting
    the crank trigger is CRITICAL and requires a machine shop.

    4. Roll your own. My choice.

    John
    -----------------------------------------------------------
    [[see above for article on knock sensors]]


    ------------------------------------------------------------------------
    From: emory!posms.cactus.org!rick (Rick Kirchhof) [not there anymore jgd]
    Subject: Re: EFI design ideas

    As to the GM ESC system, this is exactly identical in appearance to any
    1975 or later HEI system. It has coil in cap, vacuum and centrifugal
    advance in the conventional manner. It is connected to a black plastic
    box by 4 to 6 wires. The box is about 1 X 4 X 6 inches and is USUALLY
    mounted with its length along the length of the truck and parallel
    to the ground. It is often found near the power brake booster or A/C
    evaporator housing.

    The best way locate a suspect vehicle is to look for a non-computer
    controlled engine in a pickup or surburban. These are most easily
    identified by the vacuum advance can on the distributor. NO GM vehicle
    ever had electronic spark timing AND a vacuum advance can except the HEI
    ESC units. Once you have a non-computer engine, you must look at the
    distributor. If it has only one wire (usually 12 gauge, pink, this is
    power) that attaches it to the engine harness, you have a plain HEI.
    Sometimes, there is a second smaller wire for a tach or cost down
    solenoid if manual transmission. It is smaller than the power wire and
    just beside it. If it is as above, plus there are four other wires
    leaving the distibutor, you have your prize. Don't count the wires that
    join the cap to the distributor base, these don't connect to anything
    external.

    If you need to spec it out, try a 1983-85 C-10 (half ton pickup) with
    a 5.0L carbureted engine. If this gets you into on-board computer
    control, try it as a C-30 (heavy duty emissions package). The GM HEI
    ESC unit is the opposite of a standard GM electronic advance. It is
    fully advanced all the time, and looks for knock, then retards all
    cylinders equally so long as there is knock. The retard increases so
    long as there the knock continues. It waits for knock to stop, then
    adds timing back to normal settings. The distributor can be junked,
    and the module mounted and heat sinked elsewhere. Then all you have to
    do is to wire the knock controller, 12V supply, trigger coil from the
    distributor and knock sensor to it. You can use a late model divorced
    GM coil, and there you have it.

    [end]


    --------------------------------------------------------------------------------

    Newsgroups: wiz.hotrod
    Subject: Re: Point ignitions
    Date: Wednesday, Jul 22 1992 03:30:38
    From: jgd (John De Armond)

    >-> You want one? I have one I'll give you if you'll pay shipping. Junk
    >-> compared to the new stuff. The thing is not synced to spark so async
    >-> mechanical noise triggers the thing.
    >
    > I'll take it! Where should I send the check?

    John De Armond
    1631 Whitlock Road
    Marietta, Ga 30066

    > 10456017 ESG Knock Sensor $ 44.82
    > 16042121 ESG Module $164.34
    > 1894308 ign. module $ 90.85
    > -------- ---------------- -------
    > total: $300.01

    > The dealer offered a fat 15% discount, but I decided not to buy. <sigh>
    >I could probably crossbreed a knock sensor from something, and it might
    >be possible to find the module in a junkyard, but it looks like it just
    >moved 'way down on my priority list. If it doesn't rain today I might
    >cruise by a couple of the junkyards and look around, though.

    Illegitimo non carborundum (don't let the bastards wear you down!)

    That's crazy. The knock sensor is $14 from the local NAPA store.
    I found an EGS module in about 10 minutes at our only local tiny
    junque yard (yuppy haven, remember?) The ig module should be about
    $30 from NAPA. I'll check when I get a chance. When I get a chance
    I'll write up how to use it with the 4 wire $19 module :)

    > Is it really that important to synchronize the sensor with the
    >ignition? You can set the sensitivity of the Carter anywhere you want;
    >my Yamaha and most of the knock sensor equipped GM cars I've driven
    >have audible detonation before the box cuts the spark lead.

    Yes. There'll be scope screen pictures in the magazine that illustrate
    why. what appears to be valve clatter generates roughly the same
    level signal as incipient knock. The best power is made when the engine
    is in incipient ("silent") knock. That is the first problem. The second
    problem is the timing should be backed off only to the point where incipient
    knock exists. The carter unit whams the timing back to the setpoint and
    then lets it drift back up until audible knock (or engine noise) whap
    it back again. If your engine really needs knock control - as in it will
    self-destruct if not controlled - what you get is a cyclic surging
    that is very unpleasant. The next problem is only the cylinder(s) that
    are knocking should be retarded. Each cylinder may require a different
    retard. The carter whaps them all in sync. I believe but am not sure
    that the EGS unit does cylinder by cylinder control. Lastly,
    the really intelligent controllers actually analyze the waveform
    to distinguish the rather distinctive knock sound from all the other noise.
    EGS does not do that.

    > What we need in PE is a good article on "How to build your own engine
    >management system with a $3 Radio Shack soldering iron and parts
    >scavenged from your Cuisinart."

    Patience, my friend, patience. The engine management system I'm working
    on for the 2nd issue uses the Dallas Semiconductor DS5000 microcomputer-on-
    a chip. This module (cost ~$80), an A/d converter and a few switching
    transistors make up the whole thing. I will make the chip itself,
    a hard-to-find parts and PCB kit and a complete kit available from the
    magazine. I'd guess the complete kit will cost less than $300.

    Meanwhile I'm working on the $100 distributor curving machine (first or 2nd
    issue), the Fuel Injector tester (sample and first issues), finishing
    typesetting the sample, calming my blood pressure after trying for FOUR
    EFFING DAYS to get my $%^&%&%^& Linotype service bureau to make the
    first frigging sheet of film! Oh, and the new task. Buying a linotype
    machine ($10,000 used if I'm lucky.) This is fun :) Gawd, I gotta
    hire a co-op student..... Had a benevolent supporter donate an
    HP ScanJet to the project so now I don't have to redraw submitted
    artwork. This is really getting to be fun...

    Oh, back to hotrodding. Pick up September issue of Popular Electronics.
    The cover article is a CDI ignition box you can build for about $30.
    The author really does not know much about ignition but the circuit is
    fairly sound. My 5 second analysis says the spark will be too brief
    but that's easily fixed. About as cheap a CDI box as can be had.
    A single 555 timer chip would make it equivalent to the MSD box.

    Headed out next week to get my hands on a RacePack data acquisition system
    on which to do a technical review. This is the DAC all the top fuel and
    Pro Stock guys are using to do those fancy printouts after each run.
    We'll see what makes 'er tick and see how good it is. Amazin' how
    opportunities fall in one's lap once one calls himself "publisher" :)

    As of the AM, I'm off to the Datsun Z-car national convention in
    Knoxville, TN. Runs wednesday through Sunday. It's at the
    World's Fair Holiday Inn. Just come to the city on I-40 and look for
    the big golden Elephant's nut towering above the city. Head toward
    that thing and you're within a block of the motel. Anyone in the vicinity
    should drop in. I'll be wearing the very first of the Performance
    Engineering Tee shirts. :) I'll probably be piddling with the
    radar gun around the autocross and slaloms...

    Later doods,
    John


    --------------------------------------------------------------------------------

    From: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
    X-Source: The Hotrod Mailing list
    Date: Apr 1993
    Subject: Re: Stalling in a '79 Mustang
    X-Sequence: 4861

    -> I read last year in HRM about a company that makes small block ford
    -> distributers that are GM HEI on top. No more Dura-no-spark problems.

    Hey, I did that in 1981! Hacksawed the GM top off and had it welded
    onto the Ford shaft. Cleared the intake manifold (just barely) and
    worked fiiiine. Now that I have a lathe I could do it again, but after
    listening to John talk about triggering the HEI or Chrysler modules with
    points, I'll probably just use a Dura-Suck distributor housing and
    pickup and a Chrysler module. My buddy Doug is cloning a few Carter
    Knock Eliminator boxes for it. If it weren't for that and I had to
    recurve the distributor, I'd certainly want the GM HEI top - you can get
    zillions of weights, springs, and cams to control the advance, and
    they're right there on the top. Fords like to hide them underneath
    where you have to disassemble the distributor to get to them.

    [Oh my Gawd, what have I done? (I gave Dave a Carter Knock Eliminator)
    You're gonna actually create more of those things? Carter's idea
    of eliminating knock is to puke a piston through the bottom of the block!

    All joking aside, Dave, why don't you adapt one of the GM knock controllers
    instead? It at least has a chance of working. The problem with any of
    these devices that don't do signature analysis is at high RPM where knocking
    does the most damage, it is impossible in a generic manner, to
    discriminate between mechanical noise and knock. The digital controllers
    such as the J&S unit, can distinguish between knock and noise but that
    unit is kinda expensive. JGD]


    --------------------------------------------------------------------------------

    From: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
    X-Source: The Hotrod Mailing list
    Date: Apr 1993
    Subject: Re: Stalling in a '79 Mustang
    X-Sequence: 4876

    -> [Oh my Gawd, what have I done? (I gave Dave a Carter Knock
    -> Eliminator) You're gonna actually create more of those things?
    -> Carter's idea of eliminating knock is to puke a piston through the
    -> bottom of the block!

    The one on Monzilla has been in operation about ten years, still works
    fine, and was on the car when we took first place at the Divisionals.
    It beats the snot out of playing Advance Curve Man any day of the week.

    [Depends on what you call "work". I know from instrumenting the one I gave
    you that at medium and high engine speed it hears the valve train rattle
    and slams the timing back more or less continuously. Admittedly a
    Datsun OHC engine and the BMW OHC engine (I ran it on both) have more valve
    noise than a V-8 with hydraulic lifters but I doubt the box's response to a
    bit less valve noise would be much different. It DOES do a good job of
    getting rid of low speed rattle but that's mainly an esthethics issue. ]

    -> All joking aside, Dave, why don't you adapt one of the GM knock
    -> controllers instead? It at least has a chance of working.

    You *are* joking. I have been looking for one in the junkyard for
    eight or nine months. GM didn't make many of them. My friendly Chevy
    dealer wants THREE HUNDRED DOLLARS for the box, weirdo ignition module,
    and sensor. I ain't gonna pay it.

    [Whot, did Slick Willie take all the good junk yards with him when he
    left? :) First little podunk 10 acre junkyard I walked into had
    exactly what I wanted. ]

    -> discriminate between mechanical noise and knock. The digital
    -> controllers such as the J&S unit, can distinguish between knock and
    -> noise but that unit is kinda expensive. JGD]

    Isn't that one about $500? From their propaganda sheet, it looked like
    they expected you to already have a late-model, computer equipped car,
    to which you attached their box. I don't need an "engine management
    system", I just want to keep from holing a piston at an embarrassing
    moment.

    [It will work with any conventional distributor ignition. I'm not
    sure about points. I did see one in use on an old Porsche 912 at the
    Porsche club race at Road Atlanta two weeks ago. I didn't get a chance
    to talk to him because I was too busy helping another fellow work
    out his Electromotive crank trigger problem (Jon, don't say a WORD!)
    I'm going to see if I can get one of those to evaluage for the mag.]

    You keep mentioning all these wonderful systems, but I don't see
    anything that will (a) work on a non-electronic motor, and (b) doesn't
    cost the proverbial arm and testicle. I can get the spark curve pretty
    damned close with an ordinary distributor. Is the last, ultimate degree
    of timing that critical? Not in my experience. My $500 would be much
    better spent somewhere else.

    [That's a personal choice, of course. I'd spend the $500 as insurance
    against having a bad batch of gas or a mis-read timing mark trashing
    my engine. $500 is a lot of money but in the context of other
    Hi-Po parts, not terribly bad.

    For drag racing power, I agree that a simple distributor advance curve
    will do the job. No concern with midrange power or economy. For
    street hotrod motors - my main interest - I DO care about the best possible
    midrange torque and the best possible mileage if for no other reason that
    I want to skip a gas station here and there. Electronic timing control
    makes a remarkable difference in a street environment. JGD]


    --------------------------------------------------------------------------------

    From: emory!lynx.unm.edu.unm.edu!chama.eece.unm.edu!mwalker (Mark Walker)
    X-Source: The Hotrod Mailing list
    Date: Apr 1993
    Subject: Knock sensor signature analysis
    X-Sequence: 4907

    The discussions about knock sensors got me to wondering what the signal
    signature for these devices looks like. Since I work in a EE
    department big on DSP (Digital Signal Processing), I got to wondering
    about the possibility of smart (well, smarter than the OEM and less
    money than other existing solutions) use of the signal the
    sensor provides. Is this information readily available for these
    sensors?

    [See "Automotive Electrical/Electronic Systems" from Bosch. Page 133
    has some good scope snapshots taken from their narrow band sensor. I also
    have some scopemeter screens stored away around here somewhere if you're
    interested in GIF files. The OEMs will supply information on their
    sensors if you find the right person. I have some Bosch info here.]

    Oh, it also seems like I saw an article somewhere that mentioned use
    of a more common device (a microphone or something) as the sensor.
    Ring a bell with anyone?

    [There are three basic types of sensors in use. The resonant sensor,
    the narrow band sensor and the wide band sensor. A resonant sensor is
    tuned to the block's mechanical knock resonance and provides some
    mechanical selectivity. Not commonly used because so many things can
    change the block's resonant frequency. Narrow band sensors are
    also resonant but with a much lower Q. These are typical of OEM sensors.
    Wideband sensors, also called accelerometers or microphones, are sometimes
    used but the demand on signal processing is much greater.

    Do I hear a volunteer to do a DSP knock controller? :) JGD]

    --
    "There's no such thing as fast enough!" | Mark Walker
    (Or something to that effect...) | mwalker@chama.eece.unm.edu
    James Taylor | 505/277-3688 (home 899-0644)
    _Two_Lane_Blacktop_ | Albuquerque, NM


    --------------------------------------------------------------------------------

    From: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
    X-Source: The Hotrod Mailing list
    Date: Apr 1993
    Subject: Re: Stalling in a '79 Mustang
    X-Sequence: 4912

    -> [Whot, did Slick Willie take all the good junk yards with him when he
    -> left? :) First little podunk 10 acre junkyard I walked into had
    -> exactly what I wanted. ]

    We don't have junkyards around here. They all got together and formed
    a union, or something. 75% of dealer list price, take it or leave it.
    I try to find what I need at the scrap iron places first, but they
    usually don't have much.


    -> I want to skip a gas station here and there. Electronic timing
    -> control makes a remarkable difference in a street environment. JGD]

    I don't want to sound like a broken record here, but who makes one of
    these miracle boxes that'll work with my non-computer engine? All I
    need is a damned knock sensor; most of these places either sell boxes
    that plug into your existing (or non-existing, in my case) EEC-IV or TPI
    unit, or complete crank-trigger, coilless wonderjobbies that cost almost
    as much as a whole motor.

    [maybe I won't sound like a broken record either. J&S's Digital
    Safeguard box can be triggered from most anything that can fire a coil.
    From the cover letter on their literature package:


    Dear Sirs:

    Thank you for your interest in the Digital SafeGuard. We have
    included all available information, including our dealer pricing

    The enclosed four page brochure on the SafeGuard was written
    for our earlier analog unit, which did not have the rev limiter
    or built-in magnetic pick-up adapter. It does, however, give a
    good idea of a basic knock control system, so we have included
    it in the package.

    With the new system, you can set an aggresive timing curve,
    then let the SafeGuard fine tune it for maximum power in each
    cylinder, under all conditions, such as boost pressure, nitrous
    oxide injection, varying octane, altitude, humidity,
    intercooler efficiency, etc.

    The system is capable of retarding the knocking cylinder up to
    6 degree before it comes around to fire again. Total retard
    capability is 20 degrees, in steps as small as 2 degrees.

    Blown engines without intercooles encunter pre-ignition, which
    is not the same as detonation. This can trick the computer
    into retarding the wrong cylinder. In this case, a user
    programmable switch can be set to retard all cylinders by the
    same amount.

    An easily set digital rev control is also included. At the
    selected limit, program control allows two cylinders to fire,
    then skip one, fire two more, skip another, etc. For six
    cylinder engines, the program fires three and skips two. This
    rotates the misfiring cylinders throughout the firing order,
    and allows a large drop in power without stumbling or
    backfiring. Note that this is not a hard limit, but about a
    one third drop in power. We use it more as a "shift alert", as
    it gently reminds the driver to get his foot off the throttle.

    The unit also features a built in high energy coil driver,
    delivering at least seven amps of coil current to a high energy
    coil. This compares to five and a half amps in the GM HEI. No
    ballast resistor is required, simplifying the installation.

    The unit can be triggered from points, OEM electronic, or
    directly from magnetic pick-up.

    Sincerely,
    John and Shirley
    J&S Electronics

    I should note that I've never personally evaluated this unit. However,
    everyone I've talked to says it works as advertised. Retail on this
    box is $450. Kinda high but compared to say, an MSD box, rev limiter
    and "timing computer" or boost retard, it's not bad.

    The GM unit is another system that will trigger from any kind of
    variable reluctor distributor. It will probably trigger from points if
    you really insist. There's one of the largest junk yards (Longs) in the
    south just this side of Nashville on I-24 so I know you're within, what,
    maybe 3 hours of a source.

    Sorry, I just can't come up with a source of free units. But the available
    units can be had for prices that are quite in line with other high
    performance parts. JGD]



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    From: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
    X-Source: The Hotrod Mailing list
    Date: Apr 1993
    Subject: Electromotive DFI
    X-Sequence: 4919

    -> > dealer wants THREE HUNDRED DOLLARS for the box, weirdo ignition
    -> module, > and sensor. I ain't gonna pay it.
    >
    > How bout using the sensor and conditioning module from a late model
    > car, and building a seperate box to handle retarding the timing
    > (taking its input from the conditioning module).

    Nope. The system John and I are talking about is the weirdo "Computer
    Controlled Spark" from the early '80s, which appeared on assorted
    pickups and a random sampling of cars. It's a plain old non-computer
    HEI with a knock sensor box and sensor. The box is like $160, the
    special HEI module is $90, and the knock sensor another $100, though you
    could probably use any knock sensor. John can evidently waltz into his
    friendly junkyard and get them for peanuts. The only way I can get one
    is to steal it off a parked car.

    [ Actually I thought the junk yard situation here in Atlanta was pretty
    dismal. Bill Southern's little yard is nice and he's a rodder to boot
    but it's small and it is only one yard. Where I came from (Cleveland,
    TN, Odometer rollback capital of the US), there's a 100 acre junkyard on
    every major highway. There's also something like 300 licensed used car
    dealers in this little 20,000 population berg.

    So guys. What IS the junkyard situation elsewhere besides Atlanta and
    Little Rock?

    I've not priced the box but the 5 wire HEI module is about $30
    from NAPA and the knock sensor is $12. No fair quoting dealer
    prices. No one pays that much..... Do they? JGD]


    --------------------------------------------------------------------------------

    From: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
    X-Source: The Hotrod Mailing list
    Date: Apr 1993
    Subject: Electromotive DFI
    X-Sequence: 4940

    -> I've not priced the box but the 5 wire HEI module is about $30
    -> from NAPA and the knock sensor is $12. No fair quoting dealer
    -> prices. No one pays that much..... Do they? JGD]

    Unh... I'm not *that* dumb, John. I tried pricing the module - which,
    BTW, the dealer says is a seven wire part - at NAPA and other places,
    but none of them have a listing for it. I'd like to know what the $12
    knock sensor is for; the lowest price I could find was for a Chrysler
    for $38. And you still need the brain box, which is still gonna be $160
    from the dealer.

    [My knock sensor is for a Dodge turbo Lazer. Only because someone suggested
    it to me several years ago. I should note that NAPA carries two lines
    of such parts. One is "name brand" such as Standard Parts. The other
    is what the guy behind the counter calls "green box" parts because they
    are in otherwise unmarked green and white boxes. The green box parts are
    less than half the price of "name brand". I recently went to buy a
    chrysler ignition box that I pay $19.50 for. The guy laid a Standard Parts
    unit on the counter and chirped "$55". He almost had my plastic before
    it sunk in. After the roof settled and he got me a green box part, I
    laid them side by side. Same damn boxes including the various production
    markings on the bottom. The local Downeys carries the same lines so
    this green box generic line must be pretty common. JGD]


    --------------------------------------------------------------------------------

    From: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
    X-Source: The Hotrod Mailing list
    Date: Jul 1993
    Subject: Fuel Injected 2-stroke Racebikes
    X-Sequence: 5931

    -> The cylinder pressure transducer, BTW, is primarily to reliably
    -> detect knock. There has been quite a bit written about this in the
    -> last year in various SAE papers. This is vastly more reliable than
    -> acoustic knock sensors for high speed engines.

    How long do these sensors last in use? The data would be fascinating.
    Also, do you have the numbers of any of those SAE papers?

    [The intent is life-of-the-car. Suspect they're a little short of
    that goal. These are just piezo transducers so the sensor itself
    shouldn't be affected by the conditions. Heck, I have a piezo
    accelerometer here that is intended to sit on the pressurizer relief
    valve at Three Mile Island and monitor flow that will withstand aboug a
    jillion RADs of radiation, 600 degree steam and various corrosive
    chemicals all at the same time. :) 15 year old technology. Of course
    this little puppy cost about half a year's salary. But I digress.

    I don't have any papers handy at the moment but I'll see what I can
    dig up. I use the push-off-the-end-of-the-desk-into-a-box method
    of filing so it might take awhile. JGD]


    --------------------------------------------------------------------------------

    From: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
    X-Source: The Hotrod Mailing list
    Date: Aug 1993
    Subject: Fuel Injected 2-stroke Racebikes
    X-Sequence: 5933

    -> How long do these sensors last in use? The data would be
    -> fascinating. Also, do you have the numbers of any of those SAE
    -> papers?
    >
    > [The intent is life-of-the-car. Suspect they're a little short of
    > that goal. These are just piezo transducers so the sensor itself

    I'm curious about the size of the sensor, and whether it can be mounted
    up in the valve cover where it'll see oil on top. Boring a hole through
    the water jackets and into the chamber, welding in a threaded sleeve,
    and trying to clear the spark plugs, rocker gear, valvesprings, and
    ports is gonna be fun.

    [Kistler makes a combination spark plug and water cooled pressure
    transducer. Reportedly it works very well though it does require a
    charge amplifier external. Kistler also makes direct insertion
    transducers designed to thread in a drilled hole to the combustion
    chamber. These are precision, expensive lab instruments. Both Bosch
    and Hitachi have production-type sensors under development. I'm not
    sure if they'd be available to others yet or not. JGD]

    It always looked to me like a rotation speed sensor on the crank would
    be a practical way of detecting detonation. The crank flexes according
    to combustion loads anyway; when it sees an unusual load the vibration
    characteristics would change. Of course, you'd have to have enough
    detonation to make itself felt on the bottom end instead of just looking
    directly, but it'd be more sensitive than an acoustic system, and if
    you don't have enough detonation to load the bottom end, you probably
    don't have enough to hurt anything anyway.

    [I posted here about a year ago on a magnetostrictive torque sensor
    designed to fit inside the rear main bearing cap that could
    measure detonation torque. The sensor is real simple, consisting
    of a cruciform ferrite core with windings in quadrature. One
    winding is excited with AC. The resultant field is applied
    along the axis of the crank across an air gap. Torque distorts
    the field and causes voltage to be induced in the other coil proportional
    to the instantaneous torque. I don't think a commercial sensor is
    available but the SAE paper made it look fairly easy to build.
    An LVDT exciter/amp would probably read the thing. JGD]


    --------------------------------------------------------------------------------

    From: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
    X-Source: The Hotrod Mailing list
    Date: Aug 1993
    Subject: Fuel Injected 2-stroke Racebikes
    X-Sequence: 5936

    -> [I posted here about a year ago on a magnetostrictive torque sensor
    -> designed to fit inside the rear main bearing cap that could

    You sure it was only a year or so ago? I'm sure I would have
    remembered that one.


    -> to the instantaneous torque. I don't think a commercial sensor is
    -> available but the SAE paper made it look fairly easy to build.

    WHICH SAE paper?

    [Geez, makes me get up out of my chair, actually walk over to the
    book case... :) SAE Paper 900264 - "Magnetostrictive Torque Sensors -
    Comparisons of branch, cross and solenoid Designs". Published in
    "Sensors and Actuators" 1990 SP-805. He lists in the references two
    other papers, SAE 890482 and 890483. There was also an article in
    "Automotive Engineering" on the topic with pictures of the little
    sensor embedded in the main bearing cap. JGD]


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