Those little Gm modules have their own inherent problems.   Why not run a duraspark distributor with your 6al box, if you dont want a module?  

Greg B wrote:

Those little Gm modules have their own inherent problems.   Why not run a duraspark distributor with your 6al box, if you dont want a module?  

I could do that, but I've already had to replace that expensive red box once and it takes up a lot of real estate for what it does.  I'm trying to build a car that uses as many stock parts as possible.
 

Unless you just want to tinker, I don't see the point of swaping the Ford module for the Chevy. As Greg pointed out they are both mature technology that should be available at any parts house. Rock Auto has the Duraspark modules for $10 - $50, so acquiring a spare for the glove box won't break the bank. I just acquired a full Duraspark system from Rock Auto for my 429 build, including a rebuilt Duraspark distributor.

Sorry Barnett, have to disagree!  A Duraspark system does increase performance over stock coil and points system.
much hotter spark!

Msd distributor's use the same magnetic pickup as the dura spark and a 6 al is basicly a plug play deal with a duras park. In my opinion a properly curved duras park is considerably better than a hei.

I have to agree that the DuraSpark is better than the HEI. I have had a lot more issues with the HEI, especially in damp conditions when you get a lot of condensation. It doesn't seem to bother the DuraSpark.

Duraspark distributor with MSD 6A would be my choice for stock appearance and durability. I have run MSD boxes and only had issues with one that was bad when new. Good enough fir NASCAR, I figure good enough for me.
I have two 351w MSD distributors, one on the car and one near new. Hey might get replaced with DurII distributor in the future so my cobra air cleaner will fit again.

I have a system similar to yours except that I decided to go a dual ignition route. After having my MSD 6T puke in the middle of an intersection in a rain storm I set mine up with both a conventional dual points system (Ford, no vac adv) with ballast resistor for the backup and the MSD 6T/Timing Control/Selectable Rev limiter as the main system. There are three switches I need to set to select the ignition:

Power - to MSD or to ballast
Trigger - to MSD or to coil
Coil - from MSD or from ballast)

I have not had to use the backup side yet but it's nice knowing that it's there if I need it!

jkordzi wrote:

 
I'm not asking about whether anyone has substtuted an HEI-like distributor (like a DUI) for a duraspark distributor and module.  I plan on using a duraspark distributor and I'll tune the advance curve.  However, the duraspark distributor by itself is just a trigger - something has to supply the spark energy.  So my post is inquiring about whether anyone has substituted an HEI module for a Duraspark module.  Supposedly the parts store Duraspark module has reliability issues and the HEI offers some performance benefits (probably why there are HEI-like distributors on the market).  Thanks.
 

A distributor with the coil in the top of the cap will not increase a cars performance . . it is basically just a different mounting location for the distributor.
 
The pick up in the distributor is triggered by the reluctor and powered by 12 volts . . pick ups like the pertronix and mallory etc do not need a separate unit like an msd or duraspark control box to power them.
 
If you want to use a gm control box I see no reason not to.
 
If you want to use a gm pick up in a duraspark distributor, you could as long as you can mount it.

here is another description of how to wire a gm control box to a duraspark distributor.

http://www.junkyardgenius.com/ignition/jeep/HEI01.html

you can also wire a duraspark distributor to an msd box which will perform far better than a duraspark box.

duraspark control box differences.

"California was the only state in which Ford vehicles were equipped with Duraspark I ignitions, the rest of North America has never been familiar with this ignition. The Duraspark I ignition was also known within Ford as the high output ignition, it was more than a different Duraspark module, it was considered an entirely different igniton system than the Duraspark II ignition system. The Duraspark I ignition was utilized in all California V8 equipped applications in 1977, and limited to California 302 V8 applications in 1978 and 1979. The Duraspark I ignition module is identified by its RED wiring sealing block.

At the heart of the Duraspark I ignition was a special ignition coil having a very low primary winding resistance. The coil was also operated with no ballast resistance, therefore current flow in the primary windings was substantially increased in comparison to the primary current of Ford's standard (Duraspark II) electronic ignition system. The core of the coil was designed to accept a much higher magnetic charge from the increased current flowing in the primary windings, thus producing a substantially higher voltage to the spark plugs. The higher magnetic charge also allowed the coil to reach "full charge" more rapidly than Ford's other systems. Spark intensity was greatly increased ... especially at higher rpm. If this coil's primary winding was charged with the conventional "fixed-dwell" control utilized by the standard electronic ignition system it would overcharge at low rpm and overheat. Therefore an ignition module with a unique primary current control circuit was required to compliment this coil.

Differing from the various Duraspark II ignition modules, the Duraspark I module didn't control charging of the coil in the conventional way. The Duraspark I module utilized dynamic dwell, meaning the module constantly adjusted dwell based on current flow in the coil's primary circuit, independent of engine speed. This prevented over charging or under charging the coil throughout the motor’s rpm range. Dwell therefore varied with respect to the degrees of crankshaft rotation but remained relatively constant with respect to actual coil charging time; and the coil was properly charged throughout the engine's operating range.

The Duraspark I ignition produced the most consistent and most potent spark of any Ford ignition. This is Ford’s best ignition for igniting lean mixtures or rich mixtures, which was the purpose for its existence. The ignition will ignite mixtures the Duraspark II ignitions can’t. The dynamic dwell feature gives this module good high rpm performance too. This ignition’s design was more elaborate than the design of the Duraspark II ignition, and therefore it was more costly for Ford to manufacture (replacement Duraspark I modules cost several times the price of replacement Duraspark II modules)."

 

 

Last edited by barnett468 (2/28/2015 9:37 PM)

The idea behind mounting the coil in the distributor cap is threefold:

1.) It takes the coil off the top or side of the engine, reducing heat saturation. 
2.) It makes the path from the coil to the distributor as short as possible.  Even with good wires, some current is lost across the wire.
3.) It makes the ignition system easier to package and wire.

Is it inhernetly better than a divorced coil system?  Well, in true GM fashion, they started with the coil in the cap, and ended with the coil back on the intake.  They tried an Opti-Sprak system on the LT1 (que fart noise).  Eventually they went to a coil pack per cylinder with a very short wire and the coils mounted on the vavle covers.

All things considered I think you're better off with a good aftermarket setup like the Pertronix in a stock distributor or an aftermarket distributor from Mallory (not merntioned a lot, but I've had great experience with their distributors), Accel, etc.

I'd avoid the pickup from an HEI as well.  I've had the coils in these fail quite a few times.  Usually with high mileage, but you have to pull the distributor to change them.  Not something you want to do on the side of the road.