very good article below on this and test several combinations of mismatched coils and modules from different manufactures. most are no problem but it does say not to use a oil filled.
"Myth 2: Internal coils (in-the-cap) are prone to overheat.
This is probably the oldest HEI myth of all. Actually, an HEI draws only 2- to 3-amps, compared to the approximate 6-amps an external oil-filled coil draws. The lower amperage draw results in a much cooler running HEI coil. HEI Coils also run cooler because they are encapsulated in thermal epoxy, which dissipates heat more efficiently than oil-filled coils. The solid epoxy, in comparison to oil-filled coils also eliminates the possibility of leaks. You can also lose some spark intensity when you run a coil wire to an external oil-filled coil as the voltage has to travel a longer path, creating more resistance."
-http://www.superchevy.com/how-to/engines-drivetrain/sucp-0606-hei-distributors/
most likely the last time I ran it before getting the custom built Ds2 ran it and shut it off but do remember the coil temp was really high so as it cooled off it must have been to hot and fried it so hopefully this will help and going to try a camero 1987 v6 unit
QUote below is -http://cyberdave.org/HEICoilInfo.html
2. As far as I can tell the old 4-pin GM HEI modules were internally limited to about 5 amps total current flow, and had a fixed minimum dwell of some 3+ms. The dwell is probably the source of the mythical "4500 rpm limit" attributed to the stock V8 HEI distributors, at least with the coils of that era.
3. Replacement 4-pin modules from MSD, Accel, etc have an advertised 7.5 amp current limit. I believe this is the 'extra energy' they advertise over stock GM parts. (They probably also use a smaller min dwell time, but I don't know exactly what.)
4. The current in the switching module affects the energy in the coil primary to the second power: If I remember my EE courses correctly, energy in an inductor = 1/2 L*I*I.
HEI Coils:
There are several after-market coils that seem to be oriented toward the higher current capabilitiy of newer ignitions. I note the Jacobs C4 coil has advertised primary characteristics that give a saturation time of ~2.4ms (@ 7.5 amps - storing ~112 mJ). There are other coils that might be able to throw off similar energy within the single-coil V8 time constraint - a brief comparison is given below.
Coil saturation time is taken from:
[ t = - LN(1 - (IR/V)) * (L/R) ]
where t = time
LN = Natural Log
I = current (pick a max value)
R = coil primary resistance
V = Voltage (can vary, especially during starting)
L = coil primary inductance
For further reading there was an SAE paper from GM that dealt with HEI design (SAE 750346 -- HEI-A New Ignition System Through New Technology).
Coil Voltage (advertised as 'high performance' or 'hotter' coils):
The HEI information above doesn't speak to secondary voltage in the coil, but if anyone is interested there is a depiction of the general case here:
http://www.mr2.com/TEXT/DavidKucharczyk/spark.jpg
A short discussion of voltage & field density is here:
http://www.mr2.com/TEXT/DavidKucharczyk/ignition.html
A short discussion of arc time and current is here:
http://www.daytona-twintec.com/tech_ignition.html
Secondary voltage (referencing the MSD-5900 example circuit) is induced by the collapse of the magnetic field in the coil primary. That voltage follows something like V= L* dI/dT; and is multiplied by the turns ratio of the secondary/primary windings. As far as I can tell, the stock GM HEI coils used about 85:1 for this ratio. The energy transferred from the primary winding to the secondary depends on how the coil was made and the properties of the core.
The stock coil does a pretty good job as designed, but dumps energy above ~4000 rpm.
The C4 coil gives the most constant power up to 6000 rpm (if the specs are real) with a HIGH CURRENT feed.
The Jacobs can-type or the Blaster SS look like a reasonable choice for an external coil, especially if you are using a GM HEI module.
this was a good article so Looks like the blaster ss may be a good choice as even though the stock gm coil has the correct .05 ohm primary resistance it may not perform optimal above 4000rpm
I think my coil draws to much current for the stock 4 pin module to handle since it needs a low amperage draw coil under 5amps
