Converting the mopar in my 31 to hei to get rid of external ignition box and simplify wiring. I see that hei when using external coils use a E coil with a primary of .3 to .4 and I want to run a canister coil to have the right look but most canister coils run 1. To 1.5 with a few in the .7 range. Now my understanding is in order to take advantage of the variable dwell built into the hei module you need to keep the primary resistance down under .7, above that and the module goes full dwell. I see that pertronix now has a canister coil 44011 with an advertised .3 primary. Anyone see a reason why this wouldn't be a perfect coil for this? Also the next hurdle is finding a variable dwell module, I guess a few aftermarket replacement don't have that feature. Thanks gents!
I'm more of a HEI Swami. union rules dictate I can't answer a question directed at an HEI Guru. sorry.
I was looking at that coil when I was HEI shopping for my car, I would say it would work, being .32 ohms. https://www.summitracing.com/parts/pnx-44011
Actually the HEI looks for a .5 ohm coil to max the current limiting circuits. This would then rise and fall in exactly 3.6 mili seconds. If the control module isnt a period old module you might not have this circuit anyway as non of the "off shore " modules use this GM circuit. My suggestions would be just run whatever coil you now have and enjoy the ride.....Odds are you Mopar wont feel the difference. A few years ago my son and I attended the Columbus Goodguys with a Ply Valiant usinga mopar electronic ignition . Had a module go out the next day , walked thru the entire swap meet without finding a Mopar elec box. Did find a HEI complete for $15 , walked to the campground and wired it up using what wire we had, grounded it to a fender screw and started it up Mcgiver style. Tha was approx 15 years ago and its still running , my Son did clean up the wiring but its still grounded to that fender screw...
My question is... if your using an HEI, why would you want an external coil? That’s kinda the beauty of the HEI.... all in spot... neat... easy. .??? Bones
Thats also the problem with the HEI, electrical interference from mis matched parts etc. Great idea from GM but in reality the service during those years was a nightmare....... The control module however was a great part in its orginal form....We finally quit using them as ALL are off shore replacements ( including Delcos)...
Oh, ok. I understand about offshore junk! My Daddy warned me about this happening back it the sixties. Edit.... are you saying you had trouble with the GM HEI back in the day ? Bones
The dwell control is there to protect that low-resistance OEM coil, and that's the only reason it's there. Not needed with a higher 'standard' resistance coil.
Thanks guys, Bones, I'm using the stock mopar distributor to trigger the hei module so small cap with external coil. Bubba, that's what I was expecting, most if not all modules being offshore, same thoughts on the variable dwell. Crazy Steve, thanks for the reply, I thought I had read it helped gas mileage, performance, etc. But it's a mute point anyway if none of the aftermarket modules have the circuit. Thank you gents!
Every time I put a HEI in , in place of a points system , I saw an immediate improvement in performance. Haven’t done a lot, maybe 5, but they all worked good. Bones
It's not so much a variable dwell as it is a dwell limiter. Dwell is the amount of time the coil is energized. On a points system or a electronic one without dwell control the slower the motor is turning, the longer the coil is 'on', with the interval shortening as engine speed goes up. It only takes a finite amount of time to 'charge' the coil (measured in milliseconds), once it's 'charged' it reaches coil saturation and in effect you have a dead short until the circuit is broken and the plug is fired. That 'short' creates heat, and if the coil can't dissipate that heat, it burns out. The coil in a HEI system is small and poorly ventilated, same goes for coil-on-plug systems. Hence dwell control; it limits the 'on' time independently of engine speed to prevent the excess heating and allows a smaller, lighter-duty coil to be used. These coils use a low-resistance primary to make up for fewer windings while maintaining spark energy. There is no benefit in terms of mileage or performance.
I modified a slant 6 electronic distributor for my Dodge flathead and used an HEI module, much cleaner than the old Mopar boxes and no more troublesome resistors. I used a left over Pertronix 1.5 ohm canister coil from a friend’s failed Pertronix conversion and a heat sync from a 90’s Chevy truck. Being that both Mopar and GM modules are all made off shore, I keep a spare module in the glove box but I have never needed it. Make sure to use suppression wires and resistor plugs. Picture of the module and heat sync. Adam Sent from my iPad using The H.A.M.B. mobile app
Thanks again guys, especially Steve, I really appreciate the info. One last question, I'm running this on a 440, 8.5 compression, whiplash cam, some head port clean up, tunnel ram, and I do plan on playing a little at the track so with this in mind does it really matter which module I use? Proform, pertronix, etc? Reading descriptions they all pretty much all sound the same.
The better ones have a 'auto shut off' feature that shuts down the ignition if it doesn't sense a change in input after a few seconds; that protects the module. Look for that feature.... Some will also have a rev limiter if that's important to you, but those tend to get expensive.
I use the Speedway $14.99 one and they have worked great....... https://www.speedwaymotors.com/Search?query=hei+module
With my swap, I needed all the room I could get at the firewall, hence going to a small-body HEI and external coil was the way to go, plus it looks more traditional with the chrome coil.
It could help with that. It takes an old style looking cap too so it looks like a points distributor.
Along the same lines, I'm converting the Duraspark in my coupe 351W, to HEI as I need to replace the Dura box. I picked up a heat sink from 97 Chev pickup, and the module on it, is 4-wire but weatherpack, and the coil is mounted to same bracket. Can I use this later module and coil to trigger off of the Duraspark (1977 3 wire), and work in my system? I have an early 4 wire module and the Ford coil, but... Help, suggestions.
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