The easiest way to convert a vehicle with a GM engine is obviously to use factory parts and these are readily available either from the junk yards or from the aftermarket.  In case you don't have the clearance for a large-cap HEI distributor (like 1955-1956-1957 Chevrolet, hot rods, etc), small cap HEI conversions are also available (like DAVE's small-body HEI's).  GM did make a small cap distributor V8 ignition system but requires a computer for ignition control.

Dave Ray recommends using the NAPA IC12 (SMP UC-12) canister coil (1.5 ohms primary resistance) for his small-body HEI conversion, which is the OEM coil for many early GM applications.  It would be better to use a low-primary resistance canister coil (like a SMP UF6 or an Accel  8140HV) instead if you want to stick with the OEM look.  Dave Ray recommends against the use of epoxy-filled coils because an oil-filled coil is inherently better at dissipating heat and is therefore more reliable.  This is a valid argument for fixed dwell systems because those systems have more dwell than necessary at low RPMs.  The HEI system is a variable dwell design, which provides only enough current to saturate the coil.  Whether the electronic ignition system has a fixed or variable dwell, an oil-filled canister coil will run cooler than an epoxy coil.  However, an e-core's more efficient design runs cool because less energy is wasted as heat and heat dissipation is not an issue even though the windings are potted in epoxy.

The HEI system will work well regardless of whether you use the IC12 oil-filled canister coil or a D503A e-core coil.  The AC Delco D503a e-core coil provides more spark energy but requires the use of a coil wire with an HEI stud terminal for the coil.  One way to do this is with an HEI spark plug wire set, which in turn requires an aftermarket distributor cap with HEI stud terminals.

Distributor Cap & Rotor Sets

Black Cap
Red Cap

Spark Wire Set

From cap with HEI stud terminals to D503a HEI coil (with stud terminal), the following have different spark plug wire lengths than those of the early engines but may still fit.

1995 Chevrolet Truck, 5.7L, 7mm Wire Set
1995 Chevrolet Corvette OHV, 5.7L, 7mm Wire Set


We have a coil bracket that mounts the D503a and D577 to the factory coil location.  See HEI E-Core Coil Bracket.

Custom Search