Reworking a Stock Distributor to Trigger MSD Ignition Systems Part 4

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When we last left our ignition project, the distributor was pretty much buttoned up and we were down to the final setup. In the old days, you’d simply gap the points, and then when the engine was running it would be fine tuned by way of a dwell meter. When triggering an MSD ignition system, the actual MSD box looks after the dwell. All you need to do is to set the gap with a feeler gauge. For our Delco distributor, the gap (for new points) is 0.018 inches. And to recap, when using a point style distributor to trigger an MSD ignition system, you don’t need a dual point setup (which effectively adds dwell time) - nor do you need the condenser. The purpose of the point set in the distributor, and the way it is ultimately wired, is to tell the MSD ignition box when it’s time to fire. Since the point set is now acting as a simple “switch” (actually acting as a “reference” signal), with very little current passing through, it will last a very, very long time too. MSD notes that mechanical wear will be nominal as well.

Further up in the distributor, we added a high quality ACCEL cap and rotor. With the MSD ignition system, stock or replacement caps and rotors are definitely taxed. The reason is that the MSD box provides a much stronger spark than a simple point ignition will ever provide. The ACCEL rotor was designed decades ago and is still an excellent piece. For example, the rotors are manufactured from a 60,000 volt-capable alkyd compound, stress-relieved at the time of molding to ensure stability and resist centrifugal forces at high RPMs. If you look closely at the rotor, the arc ribs are tall. This helps to prevent arc-through and ignition crossfire. The rotor blade is slightly longer than stock and is built from stainless steel. The cap is also manufactured from a high strength alkyd material and the internal posts have brass inserts. The entire concept here is to provide for maximum energy transfer.

As we’ve noted earlier, the ignition system we selected to create the spark is a MSD 7AL2 (part number 7222). We’ve used these ignition boxes (and their predecessor, the MSD 7) for decades with great success. When it comes to the latest 7AL2, MSD notes: “The latest “Plus” model updates the original 7AL-2 with improved internal components – plus, our engineers added a 2-Step Rev Control and a useful diagnostic LED. Racers will be happy to see that the updated components up the voltage output and spark energy. Over 40% more spark energy, in fact! Visually, you'll notice the two terminal strips that allow for easier wiring in your racecar. The LED over the power connections will come in handy for troubleshooting, as it flashes only when the coil fires. That way you know that the coil, trigger source and ignition are all functioning properly. The mounting pattern is the same as the original 7AL-2 and is supplied with vibration mounts and several rpm modules.”

With the MSD 7AL2, primary voltage is 570. This voltage is stored in a capacitor until the ignition is triggered. At this point, all of the voltage is dumped into the coil, where it is transformed into even more voltage - anywhere from 30,000 to 47,000 volts depending on the coil, which is sent to the distributor and ultimately to the plugs.

Another big advantage of the MSD ignition system is that it can produce multiple sparks. According to MSD: “Conventional CD ignitions supply one spark of intense energy, but for a short duratio. An MSD ignition system uses multiple sparking technology to take advantage of the quick rise time and power of a CD Ignition by producing a series of sparks. More sparks equal more heat in the combustion chamber, resulting in complete combustion of the fuel mixture that produces more power. At lower rpm, there are many benefits to multiple sparks, including a smooth idle and improved throttle response – plus, the spark series prevents fouling plugs or fuel loading up in the cylinder when air/fuel distribution is poor.

“The multiple spark series of an MSD Ignition Control lasts for 20° of crankshaft rotation. At lower rpm, 1,000 rpm for example, there is plenty of time to fire the plug a number of times to ensure ignition of the fuel mixture. As rpm increases, the piston travels up on the compression stroke faster, resulting in a shorter amount of time available to refire the plug so the number of sparks that occur decreases. By about 3,000-3,300 rpm, there is only enough time to fire the plug once. From about this rpm range on, an MSD ignition control delivers one intense, full power spark.”

For a closer look at the distributor along with the balance of the ignition system, check out the following photos. Examine the wiring diagram closely too. You’ll see that triggering an MSD box with a point style distributor isn’t that difficult. Sometimes, simple is really good.

Upstairs, it’s time to set the point gap. While dwell is the method used to set up a distributor for point use only, the MSD ignition box determines dwell. You only need to set the gap. For new points it should be 0.018 inches.

The distributor cap and rotor are installed next. We used ACCEL components here, and for good reason (see the next photos).

ACCEL rotors have a longer rotor tip. That means the spark doesn’t have to travel as far to the distributor cap post.

Additionally, the arc ribs found on the ACCEL rotor are larger than those found on many replacement (and stock) rotors.

The ACCEL distributor cap is manufactured from Alkyd. The posts have corrosion resistant brass inserts and the rotor spring is steel. All of this contributes to a cap that can handle high voltage, spark surges and high temperatures.

Here’s the rotor installed on the distributor. The stock rotor screws were used.

The rate of vacuum advance is adjusted by inserting a 3/32-inch Allen wrench through the vacuum port – turning clockwise increases advance. ACCEL includes an Allen wrench with their kit.

Here’s the finished custom distributor. As you can see, building a custom distributor to fire an MSD ignition system isn’t that difficult.

This is the correct wiring diagram from MSD, illustrating how to wire a 7AL2 ignition system triggered by a distributor with points. As you can see, it’s not that difficult.

This is the final wiring setup on the MSD ignition box (less the battery + and - wires). As you can see, we used MSD Weatherpack connectors on five of the main wires.