INFO:MSD 6AL Points Trigger/OEM Tach/Duraspark/HEI

Has anyone here ever run an MSD box or any other CDI box using a point trigger?  Seems like a good setup, as the points are just switch with only a few millivolts passing through them so they have virtually no wear.  I like the ability to swtich back to points on the fly too, if the CDI died suddenly.

Edited by 72FordGTS - 13-March-2017 at 1:34PM

Thanks Johnny, I read through most of the stuff on here but no definitive answers.  Seems like people have suggested using Tach Adapters but no follow-up if they worked or not.

Thanks for the detailed response Rockatansky. 

Thanks for the info.  Still undecided which way I am going to go, but I may look harder at Duraspark if I can get it to work with the Tach.  I always thought that Duraspark needed 12 volts to coil, which is true for Dura Spark I, but Dura Spark 2 uses a resistor wire.  If that's the case, I might be able to get the Tach to work with it.  It's just too bad Dura Spark II doesn't have the adjustable dwell like Dura Spark 1.

Hey Chuck,
 
I haven't made a final decision on the ignition route, but one thing I have decided for certain is that I am converting my Tach.  I want to keep my stock dash and tach, but that current sensing tach is just way too limiting.   The Rocketman conversions will basically allow you to run any ignition system and the tach will still work and it with modern guts it will be much more accurate.
 
I am probably leaning toward converting to Duraspark.  Although the old point system worked well on my car for about 40 years of service, they old points system are just too low powered, don't offer much spark at higher RPM and finding decent point these days is pretty tough.  The Pertronix I have now is okay in that at least it stays in tune, and it may off a bit more power to the plugs, but realistically it's not much of a performance ignition especially with the stock coil. 
 
I am leaning toward doing a Duraspark conversion.  I like the OEM reliability, and I plan on using my car for long trips.  I want something that won't leave me stranded.  I also think any Duraspark system has more power than any points system and is generally maintenance  free. While a MSD box probably offers more power at high RPM, the reliability is not OEM grade.
 
I have done a bunch of reading up on Duraspark.  George Pence has probably the best info on the internet on these systems. I also pulled a few of my old service manuals and shop repair books too.  One thing I have found is many people on the internet get mixed up between Duraspark and the early breakerless ignitions.  Duraspark only came out in 1977, everything before that from 1974-76 was breakerless,ignition and was similar but not the same as Duraspark.
 
Here is a chart that George Pence made that summarizes the systems:

 
If you look at the above chart,  Duraspark I doesn't use a resister wire between the ignition switch and the coil.  So to my knowledge, there is no way you could use a current sensing tach with this setup as you'd have to eliminate the resistor wire which will eventually fry the tach.  The Duraspark II system does use a resistor wire, but the value is lower than the old points system.  I believe this was done to increase the voltage to the coil.  So you probably could use the factory resistor wire from a points car, but it will reduce the power to the coil and you'd lost some ignition power.
 
From reading up, it seems the Duraspark red strain module is the highest power module, and is the only one that has dynamic dwell.  The dynamic dwell would definitely be advantageous for a high RPM engine.  But it also seems there are a couple of issues with the red stain module.  First, it seems finding a red strain module is very difficult these days unless you want an aftermarket (off shore) unit.  I haven’t had any luck finding a Motorcraft unit.  Second, according to this old Ford parts man, they were very unreliable (see post #6 below).
 
http://www.ford-trucks.com/forums/1343344-duraspark-module.html

and here:

http://www.ford-trucks.com/forums/1203970-attn-numberdummy.html
 
The Blue strain Duraspark II system seems to be the most reliable but it doesn’t offer the dynamic dwell and less power goes to the coil due to the resistor.  It does offer timing retard at startup which is nice for running lots of initial advance.  This blue strain box seems easy to find even from Motorcraft, is cheaper, and the aftermarket wiring harnesses are all designed for this box.  This is by far the most common Duraspark swap.  I wonder how much real world performance it would give up over a red strain module.

I also wonder  if you use another coil, even a Duraspark I coil and run a fulll 12volts to this system without the resistor (the module gets a full 12volts in both systems).  I have also read about guys using GM HEI modules with Duraspark. The HEI modules have dynamic dwell and are cheap, but not sure if this setup would be reliable or if it offers any real world advantage over a stock module.
 

With the Rocketman tach conversion, it will eliminate it from the ignition circuit.  I like the idea of using the original ignition switch just to trigger a relay.  This keeps a lot of current out of the old hard to replace ignition switch and old wiring.  There is also no need to remove the resistor wire or alter the factory harness.  I actually use the ignition switch to trigger a relay to supply 12 volts to my choke and Pertronix right now, although I still have the coil power running through the circuit. so the Tach works.  If I do need a resistor in the circuit for Duraspark the Painless wiring kit comes with a resistor.

http://www.painlessperformance.com/webcat/30812

Here are the installation instruction and wiring diagrams for Duraspark I, Duraspark II that George Pence wrote up:

Edited by 72FordGTS - 11-March-2017 at 6:19AM

californiajohnny wrote: i believe the later tachs used a three wire connection like most others and not the two wire pulse voltage sensing method

Rockatansky wrote: .....but the dizzy will accept the old black points style cap, small blue electronic and the 2 piece Duraspark shown in the pic. there's also a small AMC cap with HEI towers that fits

The current set up I'm considering is using the old style small cap for a stock look. From what I've read I have to use the smaller spark plug gap as well. If that's the case I'm wondering if I can still use the more powerful Duraspark 1 box or will that only create arching in the distributor cap.    

Edited by lynchster - 11-March-2017 at 1:23PM

I have to find the article but if I remember what I read correctly the larger gap promotes a hotter spark. I'm guessing it draws more from the ignition to produce the hotter spark and could arch between the closer terminals in the smaller cap. (?)
I'm not looking for any gap in particular, just what's going to work.

Found the one based on an HEI.

Don't be tempted to excessively widen the gap. The correct gap is 0.035"- 0.040" for the majority of cases. Using plug gaps wider than that is unnecessary when using a basically stock HEI ignition. Wider plug gaps (or faulty ignition wires) cause voltage spikes in order for a spark to occur. This in turn causes the cap to fill with ionized air, and this can cause erosion/degradation to the components along with spark scatter and/or voltage bypassing to the distributor advance mechanism, shaft, etc. It is hard on the secondary ignition components in general and just isn't needed in the vast majority of cases.
The large diameter of the cap helps to prevent this and it works well enough in a passenger car, even with the wider gaps that were used for some applications. But once the RPM goes up and the cylinder pressure increases, the chance of a misfire increases dramatically with a wider plug gap.

http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor

I also found one that the one guy said it depends on the coil you use. The older coils will use tighter gaps than the newer high output ones.
It's been a while since I've revisited the ignition system for my car. I could do the older style coil but what effect does that have on a Duraspark 1 set up that the factory is calling for a plug gap of .60. The question I have to answer is can the plug gap be tightened with the Duraspark 1 with an older coil.     

Edited by lynchster - 11-March-2017 at 5:33PM

Rockatansky wrote: so can a late 76 tach be retro'd into the early gauge console housing & use the original face?   i forgot about this option, still not available yet https://www.facebook.com/permalink.php?story_fbid=10155079098013762&id=173003588761   but the dizzy will accept the old black points style cap, small blue electronic and the 2 piece Duraspark shown in the pic. there's also a small AMC cap with HEI towers that fits

Todd, when you have a chance, can you share the details of your setup, what parts specifically you used and how you wired it up?  Where'd you mount the HEI module and what did you use for a heat sink?Sounds like another great option, especially if you've used it in the real world and it's been reliable.

Some where I've got the same kind of drawing for using a Chrysler module...

72FordGTS wrote:   Yes, it looks like a late 1976 tach could be adapted to an earlier cluster. I think the hardest part would be finding one. This would eliminate the problems associated with the current sensing tach.

Edited by Rockatansky - 13-March-2017 at 2:16PM

Rockatansky wrote:   IIRC a 3 wire Bronco tach can be swapped in also?   and there was a Fox body Mustang tach too?

Here are some pics of coil and module mounts/locations. Here is a diagram or quick drawing on how I wired up my Duraspark II/5 pin GM HEI ignition module with Bosch 30/40 relays.  I used 3 separate relays, from left to right:A) 1st Relay that sends a ground signal to the HEI module's 5th pin which retards start-up ignition timing 5 degrees. The positive trigger to this relay is sent from the original Duraspark II wiring plug, WHITE WIRE is energized only in start position. The way the relay is wired changes the "+" trigger to a "-" signal to the module. Once key goes to "RUN" position the ground signal no longer exists on the 5 pin and ignition timing resumes to whatever the initial timing is set to.B) 2nd Relay sends BATTERY voltage to the "B" terminal of the module only when the ignition is in the start and run positions, the "+" trigger wire for this relay is the GREEN/RED STRIPE wire which also energizes the 3G alternator to "turn on" and charge. I used 10 gauge wire to connect the "B" module to the relay's #87 and #30 wire to the battery, the other wires used for triggering are 16 gauge.

All the connections that are from the battery to the relays are individually fused protected, as well as the "+" trigger wires.

The ignition coils I have tested varied quite a bit, here is a run down on what I have at my shop and/or acquired over the years.MSD 2F Duraspark II replacement coil: 4.66K ohms   secondary

Edited by 72FordGTS - 23-March-2017 at 12:50PM

Todd mentions he used the TFI coil with .5 ohm resistance in his setup with an HEI module.  The HEI modules need a low resitance coil.  Coil selection seems to be very important for the module to work properly.  Here is some comparisons on an HEI module firing different coils.  As you can see, the higher resistance coils produce much less energy.  This results were performed with a standard GM HEI 4-pin module, which limits the current to about 5.5-6.0 AMPS.  Some aftermarket HEI modules have higher current limiting of 7 amps or more.

Edited by 72FordGTS - 23-March-2017 at 12:39PM