As good as the GM Delco-Remy HEI is, it still lags in the performance department. The HEI distributor advance curve is severely retarded, and the stock system tops out at about 4,500 rpm. Like the points system, the advance curve is controlled by weights and springs, and like the points system the springs can be changed to allow the advance to come in quicker, preferably just off idle. The curve should be about 2 degrees at 800 rpm, 6 degrees at 1,100 rpm, 10 degrees at 1,900 rpm and full at 2,200 rpm.
The HEI coil is another area of concern in a high performance environment. The stock system generates full voltage at under 4,150 rpm. Higher rpm does not allow the stock coil enough time to recharge. Early transistors used in the HEI were limited in the amount of voltage they could handle, but today's modern control modules are capable of handling higher voltage and today's performance coils are able to recharge in about 2.5 milliseconds, good enough for usable voltage to about 7,200 rpm. Remember that when upgrading an HEI system it is imperative that you match the coil and the module.
Now that we have an understanding of the HEI, let's look at the high quality aftermarket HEI systems that are now on the shelf for today's street rods. There is an array of performance, appearance, and technical options available.
Mallory
Mallory Ignition Inc., an Industry Leader in Race-Winning Performance Products during the past 75 years, recently introduced the 85 Series HEI. The unit features a CNC-machined cast 356 T-6 aluminum upper housing with a billet lower housing for lightweight durability. The unit includes Mallory's new mechanical advance mechanism and adjustable vacuum advance, and comes with a red cap and rotor with brass inserts. They're direct plug-in replacements with OE factory-type harness connectors and are available with or without Mallory's high-performance coil. You can also get them in a Race Prepped version that features locked out mechanical advance, locked out vacuum advance with chamber removed, and includes a complete advance weight and spring kit to allow for mechanical advance conversion. Mallory's HEI unit is currently available for Chevrolet engines only.
MSD
MSD has just introduced a new aluminum billet HEI for Chevrolet engines. The MSD designed HEI module and internal coil are capable of running above 9,000 RPM (as compared to 4,500 on a stock GM HEI) and provide 50-percent more spark than a stock GM HEI. The distributor also features an oversized shaft guided by a sealed ball bearing and a long sintered bushing.
MSD also offers a small-sized Chevrolet HEI for applications that do not have the space required for the large GM HEI.
In addition, the MSD catalog also features a host of HEI module and coil kits, dust covers, and other accessories to modify or upgrade OEM HEI distributors.
Pertronix, Inc.
Pertronix's entry into HEI distributors is the Flame-Thrower Street/Strip HEI. The module and the coil are engineered to perform together, to provide ignition performance without misfires up to a minimum of 7,500 rpm, almost 3,000 rpm higher than a stock HEI. The Flame-Thrower also produces 67-percent more energy in the coil with a 45-percent faster spark breakdown time. All of this delivers twice the spark of a stock HEI to the spark plug gap. The unit comes complete with a high dielectric cap (available in blue, red or black), low-resistance center coil brush, balanced rotor, and nylon hold down screws to prevent arching at higher rpm. A factory-installed adjustable vacuum canister and a mechanical advance curve kit with precision stamped weights and center plate are also included. The aluminum housing is machined from strong but light A384 alloy and is available in cast or polished versions.
Applications include small- and big-block Chevrolets, 260-455 Oldsmobiles, 301-455 Pontiacs, and 221-302 Fords.