Car Craft
Click here to find out more!

MSD Ignition LS1 LS6 Timing & Rev Control - Build An Ignition Curve

We show you how easy it is to convert a Gen III engine to a carb with the MSD LS6 Ignition-Control Box.

Photography by

Custom Tuning
Assuming you're a card-carrying car crafter who prefers to create your own timing curves, and you're not afraid of using a computer, this little timing sojourn should show you how quickly you will be able to fine-tune your engine. There are two MSD timing graphs on a single screen. The lower screen is the mechanical advance curve where you set the initial timing, the rate, and the amount of total advance at wide-open throttle (WOT). The upper screen configures both the amount and rate of vacuum advance, which occurs at part-throttle with manifold vacuum. The MSD software also offers a three-pod gauge package that indicates engine rpm, total ignition timing, and engine manifold pressure in psia (pounds per square inch absolute). For normally aspirated systems, we would have liked to see the gauge and graph in inches of mercury rather than in psia, but the gauge does work well when working with boost pressures from a supercharger. To keep all this straight, we've included a simple conversion table.

By changing sensors, this same system can also read positive manifold pressure for boosted conditions. The term "bar" refers to barometric pressure (14.7 psi at sea level). A 2-bar MAP sensor, for example, can read up to 14.7 psi of positive manifold pressure (boost). Using a positive pressure MAP sensor, the MSD software can be easily configured to create a simple boost retard. This allows the tuner to create an aggressive ignition curve until boost is obtained, and then a given amount of timing retard per psi of boost pressure can be achieved.

The MSD control boxes also offer a two-step rev-limiter system with a low-rpm limiter that can be used for burnouts or as a launch limiter along with a high-rpm limiter. The low-rpm limiter for the two-step simply uses a blue wire connected to a switched 12-volt source. The upper-rpm limiter works anytime the engine is running, and both of these rev positions are completely adjustable. There's also a step retard (a pink wire connection) that is adjustable from 0 to 15 degrees in 1-degree increments when 12 volts are applied to the wire. It works as a single-stage retard feature when nitrous is triggered.

In the past, you would have had to purchase multiple MSD modules, retard boxes, and window switches to get all the features that this one box offers, not to mention the accuracy of DIS plus the ease of using a laptop to configure all these data points. It's the beauty of electronics that a simple little box half the size of an MSD-6A can perform all these cool functions.

Pressure in psi absolute Inches of mercury
5 10.2
10 20.3
15 30.6

Ignition Curve Basics
Basic ignition timing can be a bit confusing, so let's dig into the meat of all this to make it less intimidating. We'll start with initial timing. This is indicated on a timing light on the harmonic balancer with the engine at idle. For most performance engines, initial timing is around 10 degrees before top dead center (BTDC). Next, we'll address mechanical advance. Most mechanical-advance distributors can generate around 25 to 26 degrees of total mechanical advance. This is created by a pin moving in a slot in the advance plate of the distributor controlled by a combination of weights and springs. When you add an initial-timing figure of 10 degrees with 26 degrees of mechanical advance, you get a total advance of 36 degrees.

Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
The Don-#002
The Don-#002

great, how about a article on working a 6al2 programable with a hall effect with the allowance for boost retard.also with various msd coils available, not std ones as shown here that were hooked into

Car Craft