Installing a distributor for the first time can intimidate many enthusiasts. To eliminate some of that intimidation, we checked with Brian Caruth of Performance Distributors to help us clear the air on how to set up and time a new HEI distributor installation. With basic mechanical know-how, installing a distributor and setting the timing can be relatively easy, but it is important to be prepared. Luckily, installation is not difficult and all of the company’s Davis Unified Ignition (D.U.I) distributors come with detailed instructions that cover basic operation, installation, and timing.
First, get familiar with the distributor by reviewing all instructions included with the new distributor. Secondly, make room to work inside the engine bay. For most engines, the air cleaner is the main obstruction, but vacuum lines and wiring harnesses could also run interference. Also, make sure any loose items such as any dirt and debris, nuts or bolts, are away from the installation area.
Proper Install & Setup
There are two possible ways to install a new distributor. If the engine currently has a distributor, a notation can be made as to the position of the rotor by marking the firewall or intake. The distributor can be installed by pointing the rotor in the same direction as the original when it was removed.
Another installation method, used primarily on new builds, is starting with the number-one cylinder on the Top Dead Center (TDC) of the compression stroke. This method will allow you to install the distributor and point the rotor toward the matching terminal on the cap designated as your number one cylinder. Once that is established, follow the firing order with the plug wires in the direction of rotation of the rotor.
When converting from a points-type ignition or electronic ignition that requires a ballast resistor, it is recommended to install a designated 12-volt hot wire to ensure the distributor is receiving the required amount of voltage for flawless operation.
Items For Easier Installs
Any additional items needed for new distributor installs are minimal. A very handy tool that will make your life easier is a distributor wrench for adjusting the distributor hold-down clamp. The design and position of many distributors won’t normally allow for a socket or standard box-end wrench to be used, so a distributor wrench is a highly recommended tool. A flat-head screwdriver is best for the removal and installation of the distributor cap.
One must-have tool is a timing light. You’ll need it to make sure your timing adjustments are accurate. Don’t guess at this! Accurate timing requires the use of a timing light. Some guys will just drop the distributor in and advance the timing until they hear the engine “ping”, then back the timing off. We do not recommend this technique, especially if you want maximum results without potential engine damage. Another additional item, a small amount of cam lube can be used to coat the distributor gear for added lubrication on initial start-up. Coating the gear with engine oil is another practice that works well.
Distributor Installation Mistakes
When installing a distributor, there are a few mistakes that can be made if you’re not cautious. During the installation, position the distributor housing where the vacuum advance will not be obstructed. The vacuum advance needs clearance so that adjustments to the timing (advancing and retarding) can be made by turning the distributor housing.
Most new distributors have a vacuum canister (left) to adjust timing according to engine load. Be sure the distributor can move enough to set the proper timing. Check the timing with the vacuum line disconnected and plugged. Older point-style distributors used a ballast resistor (right) to limit the voltage and help prevent burning out the point contacts. Be sure to run a new dedicated circuit of at least 12 gauge wire for your new HEI distributor. 
Another common mistake is using an existing hot wire to power a new high-performance distributor. Switching to a high-output ignition system, such as a D.U.I distributor, from a point-type ignition or certain factory electronic ignition systems, will require the power wire to be upgraded. Most older ignition systems use a ballast resistor to reduce voltage, in order to protect the points and electronic modules from burning out. High-output distributors, such as a D.U.I unit, require a full 12 volts from the voltage regulator/alternator. A new 12-volt hot wire of at least 12-gauge in size is best to ensure maximum performance.
Be sure the power and tachometer wires go to the appropriate connections or you could damage the electronics inside the distributor.
Running the wiring for a distributor requires some caution as well. Make sure the power wire and the tach wire are not crossed during installation. Connecting the 12-volt, hot wire to the tach terminal of the coil will cause damage to the ignition module and possibly the coil, which will create a no-fire situation.
For Chevrolet small- and big-block engines, a common mistake is not checking the distributor for “bottoming” on the oil pump, a situation that can put the gears in a bind. Checking endplay is a must, especially if the heads and block have been milled. The test procedure is relatively simple, without a gasket, check the up and down play in the main shaft while the distributor is installed. Shims may be required to obtain the necessary endplay to prevent possible damage to the distributor gear and/or cam gear.
Spark plug wire selection is another common blunder when installing a new HEI distributor. High-output ignitions require a spiral-wound plug wire of at least 8MM in size to carry the increased voltage. Low-quality wires restrict coil output and performance will suffer.
One last mistake is not dialing in enough initial timing or base timing at idle. Many customers will use the engine manufacturer’s suggested initial timing setting and experience hard starts, poor idle, low performance, and bad fuel economy. The folks at Performance Distributors tune the mechanical advance curve in each D.U.I distributor to allow more initial timing, which improves overall performance from idle to the maximum RPM.
Distributor Installation Final Checks
When the installation of the new distributor is complete, it is important to check the hot wire and tach wire connections, as well as spark plug wire placement, to make sure they are in the correct position of the engine’s firing order. Whether installing new spark plugs or using existing plugs, be sure to adjust the air gap as recommended.
Check the gap of each of the plugs, even if they were used previously.
On initial start-up, adjust the base timing by turning the distributor until the desired setting is achieved. As mentioned, it is important to use a timing light for this procedure for the most accurate results. The folks at Performance Distributors strongly recommend not using a dial-back or digital timing light, as these interfere with the distributor’s high-performance electronics, and the base-timing setting will be inaccurate. Check the timing right off the balancer using an “old school” timing light. If the balancer does not have timing marks, a timing tape may be necessary. It is also important to have the vacuum advance port disconnected and plug the vacuum line to the engine while setting the initial timing.
You can use either ported or manifold vacuum for your distributor. Performance Distributors suggests using a manifold vacuum source for improved idle and off-idle operation.
Once initial timing has been set, tighten the clamp to lock it down and connect the vacuum line. Vacuum advance can be connected to the manifold for direct engine vacuum, or ported, which only supplies vacuum when the throttle blades are open. “We tend to suggest a manifold connection,” Caruth states. “This provides vacuum at idle for improved idle quality and off-idle performance.”
Now that the distributor is installed and all the checks have been made, it’s time to take the vehicle for a test drive. You want to check for idle quality, smooth acceleration, spark knock under hard acceleration, and light throttle ping. If pinging is detected under hard acceleration, too much initial timing may have been dialed in. Your new distributor will need to be retarded a couple of degrees. Light throttle ping under cruising conditions can also be adjusted by backing down on the base timing.
Taking a few minutes during the installation of your new distributor will ensure everything is done properly and you’ll enjoy years and miles of service from your new dizzy. And, with your new distributor installed and timed properly, you can be sure your engine is burning all the necessary fuel for optimum performance, drivability, and fuel mileage.
