My 1965 Barracuda was originally equipped with a points & condenser ignition system.  After I finished school in 1987, I upgraded my car to an electronic ignition and dual-field charging system from a 1973 Scamp.  For a hotter spark, I also replaced the coil with an Accel Super Coil (PN 140001), which probably didn't make any real difference in performance over the OEM canister coil.

I really enjoy taking my car for long cruises, travelling around Ontario and beyond.  With my daughter now living in Kingston, I regularly will drive the the 500 mile (800 km) round-trip in a single day so my focus is mainly highway performance and fuel economy.

With the upgrade from a Carter AFB to a Rochester Quadrajet completed and carburetor tuning in progress, I found that my fuel economy is better now than it ever was.  There is still room to improve my highway fuel economy.  That means optimizing:

  • fuel mixture
  • vacuum advance

Leaner fuel mixtures result in better fuel economy because the fuel mixture has a lower energy density, which requires more throttle.  More throttle lowers manifold vacuum which in turn reduces pumping losses.  To maximize engine torque, the pressure peak in the combustion chamber must occur at an optimum point after TDC (Top Dead Center). Leaner fuel mixtures tend to burn slower, which requires more vacuum advance.  Leaner fuel mixtures require more spark energy to ignite, which is the reason that GM introduced the HEI (High Energy Ignition) system in 1974.



The Mopar Electronic Ignition System, introduced in 1971 is essentially a more reliable evolution of the Kettering points & condenser ignition system that's been around since the 1910 Cadillac.  It still relies on a ballast resistor to control the primary current to the ignition coil.  GM's HEI system eliminates the need for a ballast resistor because the ignition module's circuitry has a variable dwell that limits the maximum current to the coil to 5.5 amps.  The coil's low primary resistance of 0.5 ohms and higher primary current allows the coil to become fully saturated up to around 3000 RPM on a V8 or around 4000 RPM on a six-cylinder engine, which is much higher than fixed dwell systems.  This results in longer and hotter spark.

There are many web pages devoted to the 4-pin HEI ignition module upgrade.

All accounts of the HEI upgrade are positive with reports of quicker starting and improved idle. I followed the HEI Retrofit Guide on the slant six forum for the most part by sourcing an ignition coil from a 96 GM V8 pickup truck and the 4-pin ignition module from a large cap GM V8 distributor.  I ran into two problems along the way:

  1. The OEM coil location on a slant is tight and the bracket I made for the HEI coil interfered with the fuel pump. I would need to fabricate a better fitting bracket. Fabricating an HEI e-core coil bracket isn't very difficult and I am working on a better design now.
  2. Spark plug wires to connect an HEI coil to a Mopar distributor cap are custom items.  NAPA doesn't sell individual parts to allow you to modify your existing high tension lead to the coil.

The simplest solution to both issues is finding a canister coil with similar performance as the e-core HEI coil.  The HEI system runs fine with the old-style canister coils used on points & condenser systems.  In fact, using the 1.5 ohm NAPA ECH IC12 coil is commonly done with GM small cap HEI conversions (see DAVE's small-body HEI's). However, these coils have much more primary resistance than an HEI coil and will therefore not be able to provide the HEI's full performance.

The coil wire is more of a challenge since it the necessary terminal and boot components are not readily available so suit GM coils.  High performance spark plug wire manufacturers can custom-make one for your needs but this adds more cost to the upgrade.

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