First, I've been running an HEI setup pulled from a late model GMC Jimmy (the kind with the module and coil all on 1 bracket) for a couple of years and really like it!

So I know the stock GM e-core coils work well, but I'm wondering what other coil options might be available with similar reliability. I'm specifically interested in the following traits: looks more like a stock canister-style coil, faster charging times, longer spark duration.

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'66 Dodge Dart

The "standard" reply is to get the round Ford coil (& its connector) for late 70s-early 80s Fords with Duraspark or some early TFI ignitions. One part # is Standard Motor Products FD476.

Another idea is to curl up with a illustrated parts guide from some company (again SMP or Napa) & find a 12V coil you like with about 0.5-0.7 ohms primary resistance.

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63 Valiant Wagon
225 - 4 bbl

Is there something special about the Duraspark coils that I'm not away of?

SlantSixDan mentioned an SAE paper on why HEI uses e-core coils and there is some very technical discussion about the design of HEI with some interesting bits about how fast e-core coils charge.

Do the Ford coils provide similar benefits to the e-core style coils?

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'66 Dodge Dart

I threw the Ford coil out there since you wanted some type of round coil. They're cheap, common- easy to find in junkyards (at least they used to be). Also fairly reliable, & decent spark output. Many of the stock Ford units were painted black- looked kinda stock. I doubt you'll find a distributor type ignition system that beats the HEI coil & module setup for function- unless you step up to some of the $$ race systems

I haven't tested the Ford coil vs an HEI, so I can't say which has more output (likely the HEI). Most all car makers moved away from canister type coils to e-coil designs 30 years ago, so that should tell you something there. (ie, e-core must be higher output, less cost, more reliability). I tend to stick to OEM type coils because that's what I see at my job & can base decisions on experience. There might be other canister coils that can match a stock HEI, but you'd have to dig up the specs.

Really, when it comes to time needed to charge the coil- it's all about primary current flow- voltage divided by resistance. So increase voltage &/or decrease resistance- this will increase (peak potential) current flow & result is a steeper current ramp until the HEI module limiter kicks in- ie. less time. GM's spec calls for a minimum primary resistance of 0.3 ohms, but I wouldn't go that far- "if you are at the end of an operating range, then you're very close to the beginning of a failure". That said most all HEI's that I've ever seen were 0.5-0.6 ohms.

Coil output in kilovolts & joules has as much to do with the design of the secondary windings as with primary power going in. The general consensus is that e-cores are "better".

As I stated in my other post (in your link), I don't have any real experience with aftermarket performance coils. There are some companies that sell canister type units that claim to have 0.3 ohm pri resistance & 60+ kV output. Don't know- don't really care. Just read some of the feedback where many complained how crappy some units were, or you had to check for manufacturing details to try & figure out the country of origin on your coil- & quess at the (lack of) durability. You do your research, pay your money, & take your chances

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63 Valiant Wagon
225 - 4 bbl

I feel like an idiot linking you to your own thread, doh!

For any onlookers, I did some more digging and found this very interesting read on CDI vs HEI ignition setups. It sheds some light on standard oil filled vs transformer style coils, most of the info I don't really understand but the gist of it is that e-core style transformer coils operate at higher efficiencies due to less inductive leakage and can nearly double the effective spark energy in some setups (specifically CDI and, to a lesser extent, HEI).

Another interesting point to note is that the article concludes that HEI, with the proper reluctor and coil, yields more spark energy than a Delta Mark 10B CDI box (considered the ideal CDI setup by the author).

I guess, I'll stick with the e-core style coil and be happy with that.

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'66 Dodge Dart

I never stopped and thought about it before, but have you ever seen images of the fields that suround a straight bar magnet? The lines of magnetic force start at one end and curve around to the other end. The e-core design frame design kinda looks like that, but in 2-D. It must help the efficiency out.

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63 Valiant Wagon
225 - 4 bbl

FWIW, I installed a brand new looking coil from a totaled Ford Taurus. Six years later it still starts first click. It's the e-coil design; I don't know if it's more efficient or less efficient than the oil canister type. But for twelve bucks including the clip on wiring harness, I couldn't complain one bit.

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If it was easy, everybody would be doing it.

As a general rule transformer style coils operate more efficiently and produce better quality spark than oil filled canisters for reasons outlined in the CDI vs HEI article I referenced.

Overall I really enjoy my GM e-core coil with weather proof connector was just hoping the technology had improved and was available in a more stock looking package. But that turned out to be a pipe dream.

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'66 Dodge Dart