Here are a couple amusing pics. Don't know if this is really cdi or just a hei module inside, but these days it could be either, regardless of wht the label says.
Years ago Jaguar used a similar box like this from the factory and charged over 400 bucks for it for replacement, all that was inside was a gm hei module.

If your msd is truly trashed, then this is an option for a heatsink.

 

Somewhere on my hard drive is a write-up using an old "duraspark" box and melting it out..using IT as a heat sink and install for the HEI 4-pin. Looks totally stock from the outside..if you so desire..

 

Not to hijack, but what exactly are the benefits to the GM HEI?

If you have a truck with a brand new duraspark distributor and a brand new ignition module, and then swap it over to the GM HEI setup, will it be noticeable? What does it offer?

 

I'm online so I'll at least give my input on the "pro's". I personally like to run a stock Ford oem TFI coil with a "duraspark" box. I have done this on other Ford products in the past and it ran fine. I have yet to run one many miles however so the durability of the "blue grommet box" with a tfI coil seems to be frowned upon at least by the "purists" who want to use a "Motorcraft" part even if the new ones ARE made overseas or who knows where..anyway...

Of course if you use a Tfi coil you don't have to worry about the wiring to it quite so much (unlike the round coil of years past..when all cars had "points", ran on 6 volts and had overdrive solenoids..passing gear etc).

It seems like the HEI option is not only cheaper, but is simpler to wire up etc...and...using a wider gap on the plugs may be possible?

just a few thoughts..

 

Those were the coolest ideas for a heat sink!!

Guys, I'm a bit perplexed, and was fishing/hoping for some help. As you read, yesterday I was pushed for time and had to get an ignition in. I threw in the 4pin and it seemed to run fine in the driveway, and it heated up real good there. I three the timing light on it, reset the carb, and was off down the road.

This morning it started fine, but I couldn't get it to stay running. Everytime I shifted into gear it stalled. I'll reset the choke tomorrow, but even with the idle bumped up it took ten minutes of warming up b/f it would not stall.

*Note: I did notice that the spark seemed weak when I had one plug out to see if I was getting any spark.

 

When I first install my 4 pin module I disconnected the “extra” ground wire (the wrist lock connector shown in the photo) while the engine was idling in the garage. It quit when I disconnected the “extra” ground. I had considered the 5th wire (GRD) over kill and probably not needed as it was well grounded through the engine block.

So I would try adding a extra ground wire if you don’t have one currently installed.
Jim

 

No, you shouldn't notice any difference with an engine in good shape. You will also not notice any difference with $700.00 worth of MSD ignition parts installed either.
The plugs will fire when the combustion chamber conditions are met, not particularly what energy the system is capable of.

If you have a poor distributer etc to start with, then I personally would go hei.
Available anywhere, cheap, very reliable.

A points system will give you up to 6500 volts to the spark plug.
A stock hei with the epoxy coil in cap will give you up to 18,000 volts.
A stock hei with aftermarket epoxy coil will give up to 22,000 volts
An hei with an external oil filled coil will give you up to 32,000 volts.
BTW the NAPA TP45 module is the same as the GM HiPo module.
Use spiral core wire with .050" plug gaps.
Coils for HEI.
Summit G5215 Chrome
NAPA IC12 black coil, or one with a primary resistance of 1.50 ohms
Both made in Indiana.
The rest of MSD and Accel etc are made in Mexico and Asia.

The module needs to be grounded properly.
Also needs the heatsink and coumpound.

As far as you msd failure, probably the same as hei, the coil starts to fail first, causing the electronics to work harder and overheat and then fail. Almost all hei module failures are from failing coils.
No epoxy coils work as well as oil filled coils just due to the heat entrapment.

 

I have quite a few posts to respond to. First, AB: I went with the 4pin b/c it was inexpensive (about $30 @ O'Reilley's, lifetime warranty), and easy to install, which was important b/c of time consideration.

Extra Ground: I ran that ground wire from one mounting bolt to frame.

You guys prob. read about the probs I had. I have to admit that I made a blunder. Although I checked the msd box for power when key was on, I did not ck when the engine was cranking. That bugged me all night, and today I hooked the box back up with the new coil and boom! It ran great.

But there is something that I can't understand: When I installed the 4pin, I had to retard the timing (clockwise) A LOT to get the mark onto the scale (about 20* --guessing--). Then, when I reinstalled the msd, I did the opposite. The timing mark is now at the extreme left edge of the scale. At the base of the dizzy I have reference marks, one on the ' collar' that butts against the block, and one on the block. I moved it about 1/2"! I don't understand how putting in the 4pin or the msd would cause the timing to read different. (I time with the v.gauge, and ck with the light). Man, all I can say is the msd loves the advance! And I use the old rule of thumb: advance it 'till it pings, and bump it back.

If I tried to advance with the 4pin it would ping so bad I could hardly accelerate. With the msd set like that, the power is noticeably better, stronger.

 

Hmmm... I cannot find what I am looking for, but somewhere I believe I read that one of the advantages of the GM 4 pin module is that it "senses" dwell requirements and adjusts for them??? Has anyone else read or heard of this?

 

The genuine GM modules and the Napa module I mentioned earlier have the variable dwell, primarily so the coil isn't over saturated at low rpm.
If you get some of the cheapo parts store modules it's a gamble, not all have variable dwell.

 

I copied this from a post by 80Broncoman on the other site, and it helps: If you get the polarity swaped between the 4 pin and the mag pickup it WILL retard the timing about 12 degrees or so AND as RPMs increase the centrifical advace will be a retard.
If you look at you base timing and then swap the wires and look again which ever is higher is correct.