Going Digital: MSD Digital Conversion

How to Convert an HEI Distributor for use with an MSD Digital 6AL-2 Ignition

By Jeff Smith

The time has come to consider the advantages of digital ignition curves. There’s nothing overtly wrong with whirling weights and spinning springs except that they’ve been around for over 100 years. Kettering was a boy when engine speed governors like these were in vogue. So let’s consider moving into the 21st Century. There are certain advantages to digital curves, beginning with very finite control over any area in the curve. This gives the tuner the ability to create the exact curve your engine desires rather than a straight linear curve that is all that a set of weights and springs can deliver. As an example, with a digital ignition, we can actually create a curve that can remove timing around peak torque where the engine might be prone to detonation. This is just one advantage to digital ignition. Of course, the price tag is generally higher with digital, but we’ve also got an idea on how to save a little money along the way. Let’s take a look at one way to take advantage of this new digital age we live in with a big-block Chevy conversion.

One of the easiest ways to enter the digital age with distributor engines is upgrading to the MSD digitally programmable 6AL-2 box (PN 6530). This box offers all the power of the classic, analog 6AL but with the benefits of digital control of the ignition curve. We’ll also show you how to convert a small-cap distributor to use with the 6AL-2 box.

We have this 496 ci Rat motor that we’ve been working on for quite some time. The engine started out with a stock 454 iron block that we bored to 4.310 and added a 4.250-inch Ohio Crank steel stroker crank and H-beam rods and a set of JE pistons. We also included a rather aggressive COMP mechanical roller camshaft with 261/276 degrees of duration at 0.050 and 0.734 and 0.737-inch valve lift with a lobe separation angle of 108 degrees. Our plan is to not only make strong horsepower but also make some serious torque since the street car it’s going into is 3,500-plus pounds heavy. We studied the AFR catalog and came up with a set of oval port 290cc heads. This might seem a bit of a surprise, but our goal was strong mid-range torque since that’s where the engine would spend a majority of its time. A previous effort with a milder 496 cam and head package with an 850 cfm Holley carb netted 700 hp, so our goal with this engine was to push the torque and the horsepower even higher.

The Digital Side

With our escalated expectations, we wanted digital control over the ignition curve, but we didn’t feel the need for an MSD 7-level box, so we looked to the programmable 6AL-2. This box operates much like the popular 6AL but uses MSD’s new Pro-Data+ software to control the ignition curve, which is optimized by using a laptop computer. This software allows the tuner to create a custom curve for his specific application. Plus the 6AL-2 offers several other features like a completely configurable, 3-step rev limiter. The first is for the burnout, a second functions as a launch rpm limiter, and the third is for peak rpm. The digital 6AL-2 also offers boost retard with control at every 100 rpm per psi of manifold pressure. Finally, if you have a nitrous system, there’s a separate trigger that will allow a single, non-programmable retard when the nitrous is activated. All of these timing adjustments allow finite adjustments down to 0.1-degree, and all of this is built into one box.

One of the requirements for any digital ignition system is that the distributor offers no mechanical advance. This is referred to as a locked-out distributor. This is because the total advance curve will be controlled digitally by the 6AL-2 box.

This is a view of the MSD Pro-Data + main screen for the 6AL-2. The main graph in the upper right is the Run-Retard input screen that we’ll discuss further in the next photo. Below the Run-Retard graph is the boost retard graph. On the far left are input options where the tuner can specify rpm points for rev limits.

This is a tight view of the MSD Pro-Data+ “Run-Retard” screen for the MSD-6AL-2. This screen works a little differently than what may be considered intuitive. In this case, we’ve set the total mechanical timing on the engine at 38 degrees BTDC. The Run-Retard curve retards the spark back from 38 degrees at each selected rpm point. For example, at 4,000 rpm, we retarded the timing 6 degrees to produce a total ignition timing of 32 degrees BTDC.

It’s worth noting that the digital 6AL-2 software operates a little differently than “normal.” When the Pro-Data+ software appears on the screen, the upper right graph is designated as the “Run Retard Screen”. This is the main timing curve screen. The system creates a curve by retarding back from the total timing dialed into the engine. Once you have the 6AL2 box wired into the car, start the engine with no advance curve built into the box. Loosen the distributor hold-down and set the timing to the maximum advance you will use with this engine. This total advance number can be more timing if you prefer. We’ll use 38 degrees as our example.

You will note in our screen captures of the MSD’s Run Retard graph that its’ best to start at zero retard and then pull the timing back to your start-run timing. You can then create a curve by retarding back from 38 degrees the amount of timing for each rpm point. In our example screen, we pulled the timing back 24 degrees, which equals 14 degrees of timing at idle (38-24 = 14). The 6AL-2 box allows as many set points as necessary to create your desired curve. The lower graph is used for boosted applications to retard timing based on the amount of boost. Once you’ve created your timing curve, you should save it both as a separate file on your computer and also to the 6AL-2 box and then you can move on to other tuning aspects like the different rev limiter settings. This may seem a bit complex, but it is fairly easy once you work with it for a few minutes.

Hard Parts

As mentioned earlier, this programmable 6AL-2 box requires the distributor’s mechanical advance mechanism to be disabled or locked out. If you have an MSD Pro Billet distributor, this is easy to accomplish.This requires removing the advance weights and springs along with the bushing from the advance limit pin. Next, on a GM distributor, remove the distributor gear roll pin, remove the gear, and lift the main shaft out of the advance mechanism plate about 2 inches. Turn the shaft 180 degrees and the advance limit pin will fit into a small hole that will prevent the advance mechanism from turning. This will lock out the distributor advance mechanism. Now you can reassemble the distributor. Another option is to purchase a locked out distributor from MSD.

These previous steps require you to purchase a complete MSD distributor that will be used solely as a magnetic trigger for the ignition. A less expensive idea for small- and big-block Chevy engines is to use a small-cap HEI distributor that was used in late ‘80s through mid ‘90s TBI trucks as well as 305ci and 350ci TPI small-block engines. This distributor uses a very similar magnetic pickup that can be easily adapted to use with the MSD 6AL-2 digital box. The conversion is incredibly simple, and the only fabrication required is to make a simple aluminum plate to cover the hole left by the stock module. We’ve done this conversion on several small-cap HEI distributors that we have retrieved from the junkyard. The most we’ve paid for one of these distributors is $10 and often they can be found for free. This same idea can also applied to Ford and Mopar magnetic pickup EFI distributors.

If you want to ensure that the distributor will work, you can check the proper function of the pickup by measuring the resistance with a multi-meter. Using the ohmmeter, the resistance between the two wires should be between 400 and 1,300 ohms. As long as the resistance is in between these numbers, the distributor will do its job. Besides the aluminum cover, we adapted an MSD wire pigtail to create the proper connector between the distributor and the Digital 6AL-2 box. On our distributors, the pickup wires are yellow and green. The green wire connects to the green MSD wire while the yellow connects to the purple MSD wire connector. Finally, we added a new MSD cap and rotor along with new MSD spark plug wires and the ignition conversion was complete.

Conclusion

Moving from spinning weights and springs to digital control might seem like a leap of faith, but once you’ve taken that first step you’ll quickly realize how easy it is to make a tuning change to your engine’s timing curve. In our experience, it often takes longer to fire up the laptop and load the software than it does to make a change in the timing curve. That’s a whole lot easier than messing with weights, springs, bushings, and the built-in inaccuracies to a whirling dervish mechanical advance mechanism. So if you’re considering this as your first bold step into the digital age – it’s easier than you think.

Parts List

We included several part numbers for reference in case you may need them, but not all of these components are required to convert to an MSD 6AL-2 digital box.