Getting good spark and a precise tune is step one for making any engine run better, but doing it with worn-out parts isn't going to get you there. Upgrading all the external components like coil, wires, and plugs is a start, but to keep your engine firing precisely, the internals of the distributor need to be in tip-top shape as well.
Replacement aftermarket distributors run the price gamut from the ultra cheap with questionable quality, to high end and pricey for guys making big power. But if you're on a budget, there is another option-you can keep your vintage HEI, and just upgrade the internals with affordable and effective mods to make it hot rod ready.
Our HEI unit was yanked from...
Our HEI unit was yanked from the tired 350 in our '68 Nova project. If you don't happen to have one lying around, used units are readily available at online and at real-life swap meets for around $20 to $40.
Usually considered the father of all modern ignition systems, GM's venerable HEI ignition made its initial appearance in a few '74 models, but became standard equipment by the following year. One of the main breakthroughs that put HEI miles ahead of previous points-style systems was its then-revolutionary expanding dwell circuit, which increased the amount of saturation time experienced by the secondary side of the coil as rpm increased. That concept brought in more power where it was needed most; under high rpm and load. Plus, without troublesome points to wear, the current carrying capacity, voltage, and spark duration all went up while the required coil charge time decreased. That's why to this day, HEI remains a staple for any hot street/strip engine that makes all its beans under 6,500 rpm.
Here's our exploded HEI next...
Here's our exploded HEI next to the Summit Racing and Pro Comp replacement parts we plan to use. There's no real science to disassembly, just a few screws and everything comes apart. This much disassembly isn't necessary unless you plan to replace the shaft bushings.
Nowadays, the ignition evolution continues with strong aftermarket support that has made rebuilding and upgrading HEIs a quick and easy project that just about any rodder can bang out in a couple hours or less-even if you're a perfectionist who takes the time to detail the housing.
| WHERE THE MONEY WENT |
| PRO COMP |
| PC1031D cap/rotor and coil |
$34.32 |
| PC6045 vacuum advance delete |
$9.36 |
| PC6043 wiring harness |
$12.48 |
| SUMMIT RACING |
| Summit Racing HEI advance curve kit |
$4.95 |
| High-output four-pin HEI performance module |
$39.95 |
| TOTAL |
$101.06 |
We won't be using a vacuum...
We won't be using a vacuum canister on our HEI, so in its place will be this plastic block-off from Pro Comp. A small clip under the base of the rotor assembly attaches the vacuum canister for advance and retard; this locked replacement uses only two screws.
Here's a step that many skip,...
Here's a step that many skip, but is always good practice-coating the bottom of the module with silicone dielectric grease for insulation and a bit of thermal transfer. Some prefer to use heat transfer paste, but be aware that it tends to dry up in hot underhood conditions whereas silicone will not.
The Summit Racing high-output...
The Summit Racing high-output four-pin performance module is the first item to be replaced. Our HEI uses the familiar plastic connector; this makes installation foolproof, but even earlier units with individual wires are designed to only install one way.
Before mounting the module,...
Before mounting the module, the Pro Comp wiring harness is connected to it for ease of installation.
We don't have new shaft bushings...
We don't have new shaft bushings or shims in our kit because unless there is noticeable slop in the lower shaft bushing, excessive endplay, or if the shaft doesn't spin freely, replacement isn't necessary. Actually, if the bushing is that worn, you'll likely need a shaft as well. Ours checked out within spec with axial endplay at about .015 inch.
All the parts self-align,...
All the parts self-align, so with five screws in place we have the electronics portion of the HEI upgrade finished. Hot rodder factoid: The once yellow (though now brownish with age) wire connector denotes this distributor is originally from a Chevy or Cadillac engine, clear would be Pontiac, and black was for Buick and Olds.
For those who do opt to remove...
For those who do opt to remove the shaft, this roll pin that retains the drive gear needs to be carefully driven out. We tapped ours back into place with a flat punch.
Our Summit Racing HEI advance...
Our Summit Racing HEI advance curve kit replaces the original mechanical advance. These weights extend outward in proportion to rpm, and production V-8 HEI units have a total centrifugal advance of 20 degrees (+/- 1 degree). Summit's kit is capable of 24 degrees. Take care reinstalling the e-clips that retain them; these things tend to fly, and trust us you'll never find 'em!
These springs completely control...
These springs completely control our ignition advance, since we have eliminated the vacuum and that directly affects how our engine will perform. We went with the heavier silver springs that most closely mimic the stockers for the planned performance range of our future engine buildup.
We've run across a few parts...
We've run across a few parts store caps that were a bit egg-shaped before; never use it if you end up with one yourself. You're risking arcing of the current as well as inviting moisture and corrosion under the cap. Our Pro Comp cap fit like a glove for a very budget-friendly price.
After attaching the pigtail...
After attaching the pigtail of wires to the 50,000V Pro Comp coil atop the ignition cap, our budget rebuild and upgrade was complete. The extra voltage will ensure we're good to run a plug gap of around .044 without losing spark intensity.
One of the most basic ignition...
One of the most basic ignition upgrades, and also one of the most immediately beneficial, is using a quality cap and rotor assembly with brass components like this kit from Pro Comp. Brass will last much longer under high-voltage use and better withstand corrosion.