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Date: Mon May 10 17:33:32 1993   
Subject: Re: Aftermarket Electronic Ignition Systems 
From: "Ken R. Dye" <>

In message <>you write:JGD writes:

>The MSD box is an excellent unit.  It makes a big differnece in idle 
>quality and low speed running.  It will trigger from either points or
>variable reluctor pickups.  The MSD-6AL contains the rev limiter.
>The MSD-6T comes with a shock resistant mounting kit that makes mounting
>the box on the firewall next to the battery very easy.  The rubber

	I just put one of these (6AL) in my 510 race car.  The difference
was night and day (although the old low-energy points system that
it replaced was getting tired); the car seem to pull much better
in low rev ranges and a bit smooth in the upper.

	I took off the solid core wires on my car, as the MSD
box had a warning label "don't use solid core wires".  Their tech
dudes said that the RF generated by this setup sometimes throws
off their Rev limiter, causing it to activate sporadically.  Too
bad, I kind of like the idea of shutting down Showroom Stock
car`s computers as I go past them.....

[Be sure to use magnetic supression wire and not resistor wire. the peak
spark current with the MSD box is, according to my measurements, over
1 amp.  You'll lose a volt an ohm across resistive wires.  If your
wires are 5000 ohms, you'll dump 5000 volts just on the wire.  JGD]

	Any way I can get the factory tach to work with this?

[Yes and fairly easily, assuming your tach is like a Z-car tach.  
If you open the tach, you'll see there is a large, large value resistor
leading from the tach input to the internal circuitry.  This resistor
scales down the rather high voltage pulses from the stock system to
something the electronics can use.  Jump this resistor out.  Then
connect the tach input lead from your tach to the "tach out" lead on the 
MSD box.  The pulse out of the MSD box is only about 15 volts so 
jumping that resistor is necessary.  Check the tach against another 
one to be sure after you button everything up.  I just drive the 
trigger input with a calibrated pulse generator and compare 
the tach with the rate I have dialed in on the generator.  JGD]


Date: Tue Jul 5 01:20:58 1994   
From: John De Armond
Subject: MSD 

>       Just how noticable is the difference when you install an MSD 6200 6A
>on an L28.   Is it worth the money or can the money be spent more 
>effectively elsewhere?

Yes.  Very much worth the money.  Only complaint I have is that it somewhat
ruins my old technique of tuning the idle mix for best RPM and then back off
a bit in the rich direction.  The ignition is so good that the RPM doesn't
vary much until the mix is VERY rich.  I can probably learn to live with
that "problem". :-)


From: emory!!jimd (Jim Davies)
X-Source: The Hotrod Mailing list
Date: Mar 1993
Subject: Re: MSD benefits (The Hotrod List) writes:

>-> I forgot to mention in my previous posting about MSD boxes that an
>-> MSD-6A will fire a spark plug whose ground electrode has been
>-> completely burned away.  It doesn't fire it real well but it does
>-> run.

> So will a plain, stone stock GM HEI.  My brother bought a '70 Camaro
>someone had dropped an HEI into.  It idled a bit rough, so we decided to
>tune it up.  When we removed the plugs, we found four out of eight had
>no ground electrodes.  Just for kicks, we used pliers to break the
>electrodes off the other four.  It idled a little rougher, but we drove
>it around that way for a couple of days.

So will a plain, stone stock GM point system ;-) I didnt believe it when
I saw it, but I got a 69 6cyl Nova to tune up one day, it started, ran smooth,
idled in drive, etc, but the plug electrodes were history.


From: Dan Malek <emory!gatech!!dan>
X-Source: The Hotrod Mailing list
Date: Aug 1993
Subject: Re: Jacob's Ignition System 
X-Sequence: 6064

In response to several ignition comments:

I had the opportunity about one year ago to help test several ignition
systems with various engines on a dyno.  It seemed some magazine
wrote an article about ignitions, and many of the customers of the
machine shop came in with their favorite ignition systems and wanted
them tested.

The quick answer is that the MSD with plain old stock Ford E-coil or
GM HEI coil came out on top.

Here are the details as best I can remember.  We tested stock, Jacobs,
MSD, and this thing called "Adrenaline" (or something like that) that
some MIT buddies showed up with.  At the time, Adrenaline had the
edge because it allowed us to electronically tune the advance curve,
and it had similar characteristics to MSD.  At the time the guys were
filing for patents, so they would not tell us much about it, but it
didn't seem like anything special.  I have not heard from them lately
to test something new.

As I said, the MSD always won, and we did not see any advantage of the
"sooper dooper" coils over the ones I mentioned above.  The MSD showed
the biggest advantage with what we called inefficient chambers.  These
were usually large chambers with domed pistons.  Engines with small
chambers and flat top pistons showed very little improvement with the MSD
over a quality stock CDI system.  Now, we did not run anything over
8500 RPM, so maybe the stock coils would give up at higher RPM and the
"sooper doopers" would hang in there a little longer.

I think the hot ticket would be MSD with electronically adjustable
advance curve.  Aside from that, the only upgrade I would make is
to buy the MSD and use one of the HEI coils.  Like John said, everything
else seems like overpriced, garden variety CDI.

We occasionally throw something else on the engine when we are dyno
testing, "just to see".  If the results ever change (and they haven't yet),
I will let you know.

	-- Dan

From: John De Armond
X-Source: The Hotrod Mailing list
Date: Mar 1993
Subject: MSD Ignition - I'm impressed
X-Sequence: 4317

I just finished repairing an MSD-7al for a friend.  Blue smoke leaked out.
Lesson here.  Don't try to run one of these things on those 16 volt
racing batteries.  Too many positrons er somethin'.

After figuring out how the thing works in order to fix it, I'm impressed.
Brute force engineering at its finest.  First a little background.

A capacitor discharge ignition is a pretty simple critter.  An inverter
steps up 12 volts to about 400 volts and charges a capacitor.  When the unit
is triggered, an SCR dumps the capacitor charge into the coil which serves
as a transformer.  A coil typically has a turns ratio of 100:1 so the
output voltage can rise to 40,000 volts or better.

The typical internal connection consists of a transformer driven by a
chopper followed by a diode rectifier and then to one terminal of the
storage capacitor.  The other side of the cap connects to the coil and
the coil connects to ground.  The SCR anode is connected to the
cap-rectifier junction and the cathode is grounded.  The low charging
current flows through the coil and then when the ignition is fired, the
SCR shunts the cap and inverter to ground, effectively placing the
charged cap in parallel with the coil.  The charge dumps to the coil and
spark happens.  This scheme keeps the coil terminals cold except during
firing so there is no shock hazard.

A problem arises in commutating the SCR (turning it off).  The current through
an SCR must drop to zero for it to turn back off.  Since the inverter
is also shunted by the SCR, it continues supplying current through the SCR
even after the charge is dumped and thus will keep the SCR turned on.  I've
built and seen in other commercial units all kinds of schemes such as
gating the inverter off during firing.  The problem with most of these scheme
is they introduce added delays which limit the RPM capability.

Now let's consider the MSD.  Not only is the MSD a high powered CDI, it
fires multiple sparks during each firing event.  That puts a severe
time constraint on the inverter and commutation scheme.  The multiple
sparks happen about 1 millisecond apart.  This means the capacitor has
to charge and the spark happen in this interval.  How do they do it?

Very elegantly, as a matter of fact.  The first indication was when I
opened the case and noticed the inverter transistor with 12 gauge
windings emerging from it.  Heavy duty.  Then I noted that the two fairly
high power transistors (2n5884) are connected in PARALLEL.  Very heavy
duty.  Then I noticed that the energy storage cap only had voltage on it
when the unit was firing but no other time. Hmm.  Time to investigate.

A little poking around with a scope showed how they do it.  Instead of the
inverter being a typical chopper, it is designed so that ONE single
half-cycle is enough to charge the cap!  When the trigger comes in from
the distributor, the inverter fires one 300 microsecond pulse that
charges the cap and then the SCR fires which dumps an 80 microsecond
pulse to the coil.  This whole sequence repeats every millisecond up to
about 8 times during one cylinder firing.

All this happens with nothing more complicated than a few transistors.
No ICs, no microprocessors, just some transistors.

This sequence, aside from being elegant and fascinating, has some
real world implications.  This single pulse that charges the capacitor
draws a peak current of over 35 amps from the 12 volt supply!  The average
current - what your ammeter would see - is << 8 amps.  If the unit is
connected to a power source appropriate for only this 8 amp load, the
amount of energy delivered to the spark plugs will be severely limited.
A heavy, direct connection to a low impedance battery is an absolute must.
Even a fuse offers too much resistance.  I've seen installations even in
Pro Stock cars that fail miserably in this regard.  This one fact may
account for the fact that some racers say the MSD box does not work
very well while others love it.

The next implication is this pulse of current is capable of introducing severe
EMI into other electronics on-board.  Particularly if the ignition is run
through a fuseblock.

MSD sells an optional capacitor (non-optional for the MSD-8) for the 12
volt leads that is highly recommended.  Their cap's retail price is pretty
severe but any 15 volt electrolytic cap of 100,000 uF or more will work


From: emory!UCSD.EDU!btree!hale (hale)
X-Source: The Hotrod Mailing list
Date: Mar 1993
Subject: Re: MSD Ignition - I'm impressed
X-Sequence: 4327

John gives a good explanation of how the MSD 7 works.  Does this
same design apply to the MSD 6 and MSD 8?

[I know it does with the -6 based on the current waveform I've observed
on the power terminals of my -6.  Dunno about the -8 though I'd bet
on it.  JGD]

Bob Hale                                      ...!ucsd!btree!hale
...!btree!                       ...!ucsd!btree!

From: John De Armond
X-Source: The Hotrod Mailing list
Date: May 1993
Subject: High Voltage Warning
X-Sequence: 5172

I've just finished repairing two MSD-7AL ignition boxes for a friend who
shall remain nameless in order to protect the guilty.  One I had fixed
about 3 weeks ago.  The other one MSD had fixed at about the same time.
Both died while being used on his dyno.  The same thing killed both of
them.  High battery voltage.  This note is a warning as to how to avoid
the problem.  Fortunately the "fuse" in the -7 box is the power
transistors that only cost about $10.

Based on a hunch from seeing how his dyno room is configured, I sent him
a small stripchart recorder locked in a box with instructions to
connect it to the battery on the dyno used to start the motors and
to let it run for a day and send it back to me.  The results are

The dyno sits unused for long periods of time so the standard fare is
to roll over the shop battery charger at the beginning of a test run,
hook it up and slam it on fast charge.  There it sits until the test
session is over.  Therein lies the problem.

When the battery is new it can take this treatment.  Fast charging does
shorten the battery life but it can generally take the current without
the terminal voltage increasing too much.  Not so as a battery ages
and its impedance rises.  The typical garage quick charger is a fairly
high voltage, fairly high impedance power supply designed to force
lots of current into the battery regardless of terminal voltage.
Open circuit voltage can be 20 volts or more.

What I saw happen on the dyno battery was the quiesent voltage sitting
at about 11.5 volts which indicates a sick battery.  When the quick
charger hit it, the voltage quickly rose to 16 volts and crept up
to over 20.  MSD boxes start getting annoyed at about 15 volts and
will puke a transistor or two at your feet at around 16 or 17 volts.
That is exactly what happened to both of these boxes.

The lesson here of course, is if you're going to use a quick charger,
disconnect the battery from everything.  This is particularly important
with fuel injected cars because the fuel injection computer typically
has voltage on it all the time


From: <Jason.Torque-Addict@Rutgers.EE.Department>
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: MSD Timing Control
X-Sequence: 6238

	Recently, I installed an MSD HEI Adjustable Timing Control in
my carbureted Pontiac. The unit was a simple three wire hook-up, with
one wire to the positive side of the coil, one wire to the negative
side of the coil, and a ground wire.

	I don't understand, however, how this unit adjusts the timing
since it is hooked in parallel with the ignition coil and the HEI
ignition module. My only guess is the timing control shorts out the
coil, and after an ignition pulse from the ignition module is
received, the timing control sends another ignition pulse after a
certain delay. Does anybody have any more information? If this
was the case, it would seem the control has to accept quite a bit
of power and heat.

	Also, how is the timing control able to advance the timing,
since it must now fire the coil BEFORE an ignition pulse is
received? Does it just "guess" based on timing control setting and
engine RPM?

	As of yet, I have been quite pleased with the unit, since
it can vastly reduce (though not totally eliminate) pinging when
flooring the accelerator on a rather steep hill.


[I've not actually played with this unit but I'll speculate based on
how MSD does it with other retard modules (and about the only way I
can think of to do it).

The unit can't advance the timing past when the HEI triggers for obvious
reasons.  What it CAN do is establish some amount of retard as "normal".
When you set the mechanical timing under this condition, you are
actually mechanically advancing the timing.  The "normal" retard in
the box makes the timing "right".  When you turn the knob to "advance",
you're actually only lessening the electronic retard.  You can check
to see if this is how it works by checking the timing marks with and
without the box being connected.  Bet you'll see the timing go way
advanced when you disconnect the box.

How it actually works is it detects the firing of the HEI module by
detecting when coil current diverts from the now-open transistor in the
HEI module to the transistor in the box. (clever)  It phase locks an
oscillator to the pulse rate and the pot simply varies point between
pulses when the box triggers.  It relies on the HEI module staying off
for a few degrees and being off when the box fires.  This unit probably
wouldn't work with the "high performance" HEI modules that crank up the
electronic dwell (turn the transistor back on quickly after firing).

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Jacobs Electronics Ignition
Date: Fri, 21 Sep 2001 19:27:30 -0400

Bill wrote:

>  After quite a few year of playing with cars my exoerence has been,
> First I bought and installed an MSD on a jeep it failed 2 years later
> . called the tow truck . That the jeep was used very rarely. Called
> MSD and the said just send it to them along with 50 something dollars
> and they will repair or replace it , thats their standard policy.
> Second was a chevy pu I bought that had a MSD on a 350 sbc  failed
> after 1 1/2 years. The previous owner also gave me the reciept showing
> it had just been installed prior to selling me the truck , it also
> rode back to my shop on the tow truck . I have found thru the years
> that the most improvement that can be done for the money bar none is
> to upgrade the spark plug wires to premium top of the line wires at
> least 8mm .If you have a coil you can get to, also upgrade it to a
> premium top of the line one.For some reason ($) manufacturers only use
> adaquit (sp) wires and coils.

Interesting.  I've installed hundreds of MSD systems on customer
cars and my own.  I also used to run an independent repair depot for
MSD boxes.  My experience has been that the box is bullet proof
unless grossly over-voltaged.  There is a particular part in both
the -6 and the -7 series that always fails from the over voltage.
The two usual causes are either a) trying to run a 16 volt "hotshot"
racing battery or b) demonstrating how sharp you are by pulling the
battery terminal with the engine running to "test the charging
system".  The typical >30 volt spike will cook the box, along with
most other 12 volt electronics on the vehicle.


From: John De Armond
Date:  Mon Jun 3, 2002  9:26 pm
Subject:  Re: [megasquirt] Re: fed up.... going to use msd...
X-Source: The Megasquirt mailing list

On Sun, 2 Jun 2002 09:01:36 -0400, "Lo Custom" <locustom@e...> wrote:

> If you guys plan on getting a MSD unit I recommend looking into their
>digital line. The good old MSD 5,6 or 7 are the biggest noise producers
>made. I know of two DYNO operators that will not dyno your car if it is
>equipt with a standard MSD box due to the noise that is emitted from these
>units and how it effects their test equipment.

OTOH, just about every SuperFlow that I've worked on (I used to offer
independent SuperFlow service) has a -6 or -7 box bolted to the
instrumentation bulkhead. Those boxes have produced the best numbers and
numbers sell engines, as opposed to race results, believe it or not.

The reason the MSD boxes cause problems is that people don't understand how
they work and therefore do not wire them properly.

The basics of capacitor discharge ignition are that an inverter charges a
capacitor to 350-450 volts or more and then an SCR triggered by the engine
dumps this energy to the coil. The coil acts as a simple transformer rather
than an induction coil and steps the voltage up according to its turns ratio.

The MSD variation on this is that at low speed, it fires this sequence
multiple times on each ignition event. In order to be able to fire multiple
sparks very rapidly, the capacitor charging circuit is novel. It charges the
cap with one large half wave current pulse through the internal step-up
transformer. This pulse has a peak current of more than 30 amps in the case
of the -6 box. Closer to 80 amps for the -7. This is the root of the

Though the -6 box only draws an average current of about 8 amps, it does so in
bursts of 30+ amps. Therefore the wiring has to be sized for that kind of
current. Moreover, since the pulses are fast, the wiring has to be of low
inductance and that means short, direct runs to the battery. I try to mount
the box right beside the battery whenever possible. No fuses in the line -
they offer way too much resistance. Don't worry, the MSD will gleefully smoke
itself to protect the battery when it malfunctions :-) Because the pulses
have fast rising and falling edges, there is are high frequency components
which will radiate from the wire if not taken care of. Twisting the main red
and black heavy power leads does wonders for this problem. Finally, using the
surge capacitor that MSD sells (or any low ESR electrolytic of similar rating)
and mounting it as close to the box as possible will clip off the bulk of the
noise and reduce the surge the rest of the system sees.

The other side is dealing with the EMI produced by the fast switching of the
high voltage to the coil. Twisting the coil primary wires again helps
greatly. So does the use of Magnetic Suppression Wire for ignition wires.
This is practically mandatory since the near 1 amp peak secondary current will
rapidly degrade and destroy resistor wires while solid ignition wires will
quickly harm the MSD box while radiating enough EMI to stop a tank!

Making sure the rotor is properly timed to the cap helps a LOT too. With lots
of advance, the rotor conductor can end up away from the cap contact and
result in a series of long, highly electrically noisy sparks. Rotors with
wide contacts are available and in extreme cases it is necessary to remove the
reluctor and alter its timing to better align the spark with the rotor

Do all this stuff right and there is no noise problem with an MSD box. I use
the boxes on every vehicle I have and have NO noise problems with any of my
electronic equipment.

> Are you still using points or a Pertronix unit? I believe the MSD
>Digital will work with the Pertronx unit. These are suppose to be real good
>with giving off noise and such. Just an idea,

I'm pretty underwhelmed with the Pertronix unit. It fulfills a niche which
is, stock appearing conversions. But if there is an electronic distributor
available for the engine at hand and stock-appearing isn't an issue, I'd go
with the new distributor.


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