Swapping in a new HEI, or even just pulling one out to service, is quite simple. All it requires is basic handtools and some background info on how the distributor works in conjunction with the engine. Small slipups here could require major troubleshooting later to figure out why the engine won't idle properly and why power lags. It's easy to understand why so many do-it-yourselfers get frustrated when trying an install for the first time-many small items cannot be overlooked. Things like engine-timing position and distributor shaft position all play a role in the function of the distributor, and if they're not given proper attention, the distributor will not fall into place.
HEIs have a too-good-to-be-true reputation. Plop one in and you're set, which makes them the perfect way of dispersing spark among your eight cylinders. However, like many engine components, parts do wear out, and when they do it's time to replace them. Our case here is a perfect example. This big-block was nothing special; it provided everyday grunt with iron heads, 2-inch headers, and a Holley 750 carburetor. But its old HEI unit couldn't be timed correctly because of a worn-out shaft. It was time to swap in a new unit from Davis Unified Ignition (DUI). The best part is these gems from DUI can be custom-tuned to your application, which only takes a quick phone call to Davis-have your engine specs ready.
We got this big-block running in about an hour, but first-timers may take a bit longer and having help speeds things up as well. As you can see from these step-by-step instructions, replacing your old unit with a fresh Davis Unified Ignition HEI is almost too simple. Just watch out for those pitfalls.
Quick Notes
What We Did
Pulled out the old HEI and swapped in a brand-new unit from DUI (PN 12720)
Bottom Line
It won't take long to get that big-block correctly timed and running sweet
Cost (APPROX)
$250
 Joe Rubio is no rookie when...  Joe Rubio is no rookie when it comes to working on his favorite El Camino. He frequently wrenches on it at his auto body shop, which is also where our Project Brutus is getting all its bodywork done. After popping the hood on the '80 El Camino we needed to land the engine at top dead center (TDC). Since the big-block is in the engine bay, all we had to do was bump the ignition with the key until the timing pointer marks matched up with the front balancer. To double-check, we also pulled the No. 1 spark plug and plugged the hole with a finger. As the motor comes to TDC, the compression will push your finger out. |  From there, we began to remove...  From there, we began to remove anything that would slow us down. Rubio disconnected vacuum lines and the throttle cables. This would leave us a clear path to remove the old stock GM HEI. |  We went through and disconnected...  We went through and disconnected all the spark plug looms and wires. Then, using a long Phillips screwdriver, we removed the cap |
 To get the old distributor...  To get the old distributor out of the hole, we used a 9/16-inch open wrench to remove the clamp, then we disconnected the ignition wiring. Rubio then pulled the distributor straight up and out of the engine. We took special note of the position of the rotor. The new HEI needs to fall into place just as the old one did. |  To get the new distributor...  To get the new distributor ready, we pulled the new cap off the Davis Unified Ignition (DUI) unit using the same Phillips screwdriver. We turned the rotor and shaft to match the same position as the old HEI. |  Distributor gaskets can be...  Distributor gaskets can be reused. Since ours wasn't torn, we simply placed ours onto the shaft. |