Since their inception at the start of the 20th century, motor vehicles with gasoline burning engines have needed a precise way to deliver an electrical spark to each of the engine's cylinders. (Note that diesel engines do not rely on an electrical spark to ignite the fuel-air mixture.) For much of the past 100 years, the spark has been delivered by the ignition distributor. The distributor is always mechanically linked or timed to the engine's rotation so that the spark is sent at the exact moment it is needed.
Because distributors do wear and need replacement eventually, we've created this article to discuss performance distributors with electronic upgrades and other design improvements over OEM - for classic vehicles as well as newer ones. In many cases, these distributors enhance performance and reliability compared to original designs.
How Distributors Work
Looking at how a distributor works, you’ll find a shaft at the center of the distributor with a rotor at its top. This rotor spins under a distributor cap. The cap has a number of terminals around its circumference, equal to the cylinder count. As the rotor passes under each terminal, electricity travels through the cap, and out into a spark plug wire, leading to each spark plug. A set of points and condenser sit on a plate under the cap. The opening and closing of the points, once for each cylinder for each rotation of the rotor, helps create the high energy spark from the ignition coil.
The distributor shaft may be driven by a gear on the crankshaft or camshaft. As engine speed changes, so does the need to change the exact moment that the spark is delivered to each spark plug. Before the widespread introduction of electronic controls in the 1970's, ignition distributors performed this "advance" through a combination of a vacuum advance unit (which draws from intake manifold vacuum pressure) and/or a centrifugal advance unit (using springs which move from centrifugal force as the distributor spins more quickly).
For many years, engines required a lot of routine maintenance, and much of this was focused on the distributor. Points, condensors, caps, and rotors were all considered maintenance items which needed replacement once a year or more. Distributors with mechanical advance units would lose their calibration and needed to be adjusted. Over time, bearings and seals would wear. Distributors would need to be rebuilt or replaced. In all these cases, the driver would likely sense that things were not quite right as performance and fuel economy suffered.
In the mid-1970s, high energy ignition systems were developed that integrated the ignition coil into the distributor, and used hall-effect optical triggers instead of breaker points. More advanced ones uses capacitors and computer modules in what's known as a "capacitor discharge ignition" system. In this setup, a charging circuit charges a high voltage capacitor. An instant before ignition is due to occur, the system briefly halts charging the capacitor so that it can discharge its electrical output to the ignition coil and the spark plug.
Many distributors used with electronic fuel injection engines do not have vacuum and centrifugal advance mechanisms. On such “chip controlled distributors”, the timing advance is controlled electronically by an engine computer. Timing can be adjusted more accurately based on a wider variety of factors - not just rpms and intake manifold vacuum. Eliminating hardware for centrifugal advance and vacuum pressure creates a more reliable distributor with fewer moving parts to wear out.
Whether they are equipped with points or not, all distributors are subject to wear of the bushing(s) that surrounds the main shaft. When this happens, the rotating shaft can wobble to the point where spark doesn't flow properly - causing inconsistent engine performance as rpms change. If the wobble becomes bad enough, the reluctor wheel can collide with the coil - causing total failure and a stranded vehicle. Oil can squeeze up the shaft where it doesn't belong and cause problems.
Even if vibrations on the shaft are only minor, eventually they'll cause mechanical and vacuum advance counterweights to stick, pivots to wear, and springs to lose tension. The inconsistent spark that results is weaker, and the incomplete combustion generated because of it will cause poor performance, hard starting, reduced fuel economy, rough running and excessive emissions.
Tips When Upgrading Your Distributor
Professional engine builders agree there's a huge advantage in upgrading an older car with a points-type distributor to one with an electronic setup. Ask one, and they'll tell you it really wakes an engine up, helps achieve better mileage, and allows smoother running at all rpms. It also eliminates a pesky maintenance item.
They'll also tell you to look for a high-quality HEI type distributor that has a good housing, gearing that's been machined (not cast), and a strong cap with a good diameter to prevent cross-firing. We agree, and we feel you'll find some of the products we offer very intriguing - and worth a look if you own a vehicle built before the turn of the millennium.
Performance distributors offer a number of enhancements over the original equipment designs. For example, many feature a billet aluminum housing that saves weight without giving up strength. Distributor shafts are “centerless ground”, which creates tighter tolerances and smoother surfaces (less wobble and shaft bushing wear). Brass cap contacts conduct better and last longer. And shaft bushings are designed to hold together during sustained high rpm operation.
Quality distributors for older vehicles will often offer upgrades in the form of self-lubricating bushings, heavier-duty points, and brass condenser casings that resist corrosion. Look for a distributor that allows individual points to be manually adjusted so you can overlap dwell intervals and increase electrical charge in the coil. A distributor that also offers adjustable mechanical advance lets you tailor the timing to match the power curve you seek for how you'll be using your engine the most.
For vehicles up to the mid-1970s with older style distributors equipped with points and condensers, consider upgrading to a replacement distributor with two sets of points instead of a single, OEM-style set. Because the current is split between twice as many points, normal wear is cut in half - sometimes more. Under hard driving or extreme climate conditions that can cause points to burn away in a few thousand miles, dual point distributors have a higher rate of survival.
If you're running higher-voltage spark plugs for more power, a dual point setup is the only way to get a larger amount of current through the ignition coil without frying the points. That said, you don't need to race your vehicle to enjoy the longer life and reliability offered by dual point distributors.
Should you decide to upgrade your older Ford or Chevrolet/GM vehicle from a factory carburetor setup to aftermarket fuel injection, you may run into problems when the add-on computer for the fuel injection can't determine which cylinder is #1, and when it's at top dead center during the compression cycle. You'll need a distributor that's built to fit your older car and equipped with a hall effect sensor that tracks this necessary information.
If you've got a Ford with a fuel-injected V8 engine built between the mid-1980s and mid-1990s, your factory distributor is equipped with Ford's EEC-IV electronic engine control module that's gray in color and mounted directly to the distributor. These are known as "thick film ignition" (or TFI) modules, and they use the distributor to trigger the ignition and distribute spark. Because of the integrated module's close proximity to heat and vibration, it (and the entire distributor) is prone to failure. Replacement distributors for these Ford TFI setups offer a far less troublesome arrangement, clear most aftermarket performance fuel rails, and feature upgrades such as a billet aluminum housing that's lighter in weight without loss of strength.
If your vehicle was built with a capacitor discharge / high energy ignition setup and you want to use it for high-rpm extended track racing, look for a distributor with a magnetic pickup and module to trigger the timing. A magnetic pickup consists of a permanently fixed magnet that creates a magnetic field. Rotating reductors disturb the field, and the changing magnetic flux induces voltage. There's no need to adjust dwell, and you'll only need to set timing once because it won't change.
To help guide you through the selection of these distributors and many more, we have set up the Performance Distributors area of our website to provide you specific choices that will fit your year, make and model vehicle. Once your car's information is provided, you'll automatically see all applicable choices. Treat yourself to a new high-performance ignition distributor, and fall in love with your car all over again!