The Ins And Outs Of An MSD Ignition System

To some, wiring a vehicle or working on your ignition system can be a very daunting task. Unlike other issues that can happen within various aspects of your ride, spark or misfiring issues can’t always be diagnosed as easily as a warped rotor or a hole in the radiator. However, spark is just as crucial to your engine’s success and health as the air and fuel it’s receiving.

MSD ignition

Inside the Digital 6AL, you’ll find a microprocessor that monitors and controls every firing and rev limit. The circuits are updated with efficient components that help the ignition produce more power while drawing less current! In fact, the Digital 6AL delivers over 530 volts to the coil with up to 135mJ of spark energy for every firing!

Many have fallen victim to fighting ignition issues because they don’t properly understand ignition systems and how they work. Instead of constantly fighting this battle or paying someone to work on your ignition, many misfires can be solved by looking back at the basics of an ignition system.

We went to the experts at MSD who offer a ton of ignition educational materials on to take a close look at the basics of ignition systems. “The basic function of the automotive ignition system is to produce a spark that promotes the combustion of the air and fuel mixture,” explained MSD’s Todd Ryden. “The spark that the ignition produces must arrive in the cylinder at the perfect moment in the combustion stroke and have enough voltage to jump the spark plug gap.”

The fact the ignition system operates with a high-output spark thousands of times in a minute is something most of us take for granted – Todd Ryden

“The fact the ignition system makes this all happen at the right moment with a high output spark, thousands of times in a minute, is something most of us take for granted,” said Ryden.

Every Ignition Has Two Sides

MSD summed up for us on their educational site what is exactly happening within the ignition process: A typical (meaning stock) 12-volt automotive ignition system operates by taking in a low voltage with high current from the car’s battery and changing it into a higher voltage with lower current to jump the spark plug gap to propagate combustion in the cylinder. This process of changing low voltage to high voltage, called induction, takes place in the coil. From there, the high-voltage spark is transferred to the distributor and on to a spark plug wire which must deliver the spark to the cylinder that is coming up on the compression stroke.

That’s a lot of information at once, but to help break down the entire system, MSD recommends examining the ignition system process as having a primary side and a secondary side. The primary side is the parts or components that deal with converting low voltage from the battery to the high voltage. These parts include the battery, the ignition switch, a switching device and the wiring that connects to the coil’s negative and positive terminals.

MSD explained to help better understand an ignition system it is easier to break it down in two sides – a primary and a secondary side.

As you can see from the above diagram the coil is the only component that performs functions in both the primary and secondary side of the ignition. The spark plug wire that connects the coil to the center terminal is where the ignition system starts to perform the secondary side of the ignition system.

The secondary side occurs when the voltage is converted to sometimes as high as 20,000 volts within the coil and then delivered to the distributor. From here the voltage will be delivered to each individual spark plug with a high enough voltage to jump the spark plug gap at the perfect time and cause combustion.

What Is Happening Inside Of Your Coil

Since the coil is involved in both the primary and secondary side of the ignition system, it’s easy to see why it can very easily be misunderstood, “The coil is an incredible part of the ignition system, if there is any part that resembles a magical black box – it’s the coil.” Ryden explained. The coil is responsible for receiving 12-14 volts and then delivering an output of 15,000 – 20,000 volts depending on your application.

Within a coil, you will find two sets of windings made up of insulated wires that surround an iron or similar metal core. These primary and secondary windings are responsible for creating the extremely high voltage that it takes to jump the spark plug gap.

So how do the windings and core take 12-14 volts and turn it into 15,000 volts or more? MSD explained in-depth just how this occurs: In a typical factory-style inductive ignition, current from the battery flows through the thicker primary windings when the switching device (points or magnetic pickups) is closed. This creates a magnetic field that builds strength thanks to the help of the iron core. When the switching device opens (the trigger signal) the flow of current is broken and this magnetic field collapses over to the thousands of secondary windings. During this collapse, the voltage is stepped up, creating the higher voltage that is required to jump the spark plug gap and ignite the air/fuel mixture. This process is called inductance.

Understanding Timing

The ignition system only works if the spark jumps the spark plug gap at the perfect time. This is why it is so crucial to check the timing of our engines to ensure that the spark jumps the spark plug gap at the exact moment to achieve the ideal combustion event for the engine. “The biggest mistake we see people making involving their ignition system is not understanding timing correctly,” Ryden told us.

Taking Care Of The Fire

MSD’s Basic Distributor Maintenance Tips:

  • It is recommended to inspect the cap and rotor at least once a year. If you live in an area with high humidity, you may want to inspect it more often.
  • Visually inspect the cap and rotor for wear of the cap terminals and the rotor tip.
  • Look for traces of carbon tracks where spark scatter occurs.
  • Visually inspect the plug wires for burns or tears. Also, it is a good idea to periodically check the resistance of the wires to see if there is a wire with excessive resistance indicating a break in the conductor.
Defining Timing Terms:

If you are new to ignition systems and understanding timing, we need to define a few terms that you will see in the next few paragraphs about the timing of an engine.

  • Retard Timing – When the spark occurs later in the compression stroke. The air/fuel mixture doesn’t have enough time to fully ignite which results in less force to push the piston.
  • Pre-Ignition or detonation – When the spark occurs too early when igniting the air/fuel mixture in the combustion event. This will also rob the engine of horsepower and possibly damage it.
  • Top Dead Center (TDC) – when the number-one piston is at the top of the number-one cylinder.

As RPM Increases, The Timing Must Also Change

In theory, timing is easy to understand – the spark has to be delivered from the distributor at the perfect time to achieve maximum combustion and more importantly, the most amount of horsepower. However, the ideal timing setting starts to change as the engine’s RPM increases. As the piston starts to travel faster on each compression stroke, the spark has to occur sooner to keep up with the demands of the engine.

MSD explained to us how distributors are equipped with an advance mechanism to meet this demand: At idle, a spark occurs on a piston’s compression stroke a few degrees before it reaches TDC. At this point, the fuel mixture is ignited beginning the combustion process. The act of combustion remains fairly constant but because the piston is traveling at a much higher speed, the initiation of the combustion process needs to occur sooner. Therefore the spark must occur earlier in the compression stroke to generate the best combustion and power results. To meet these demands, distributors are equipped with an advance mechanism that operates through centrifugal force.

MSD ignition

We check the timing at idle as well as at a higher RPM to see the amount of advance the distributor is creating.

Advance is extremely crucial to the power your engine is creating. Too little advance can hinder the performance of your engine, while too much advance can cause pre-ignition. This is why you must check the timing at idle and higher RPM to see what the total advance is.

Mechanical advance occurs within the distributor by two weights that sit on an advance plate which is attached to the trigger assembly. As the distributor spins quicker, the spinning force pushes the weights outward and results in the ignition being triggered earlier. Attached to these weights are springs that control the rate at which they move, by changing springs you can affect how quickly the advance occurs.

Factor Advance Timing for: Retard Timing for:
Cylinder Pressure Low High
Vacuum High Low
Energy of Ignition Low High
Fuel Octane High Low
Mixture (Air/Fuel) Rich Lean
Temperature Cool Hot
Combustion Chamber Shape Open Compact
Spark Plug Location Offset Center
Combustion Turbulence Low High
Load Light Heavy

Many of MSD’s Ignition boxes offer the ability to adjust the timing right on the ignition box. For instance, the Programmable 6AL-2  connects to a PC where the user can map out a timing curve for their application. This allows you to precisely program ignition timing for optimum engine performance. Though we have to mention, this process should be left to trained tuners.

Introduction Into CD Ignition Systems

Up to this point we have mostly covered stock ignition systems which are classified as a inductive system because they rely on the coil to do the heavy work. These ignition systems do a decent job of creating combustion within an engine. However, if high horsepower is your goal then MSD suggests you should look at a capacitive discharge (CD) ignition. “The biggest advantage of a CD ignition system is its ability to produce full-power sparks through the engine’s entire RPM range with no fear of a weak spark at the top end,” explained Ryden.

The biggest advantage of a CD ignition system is its ability to produce full-power sparks through the engine’s entire RPM range with no fear of a weak spark at the top end – Todd Ryden.

The CD ignition draws voltage supply from the battery and steps up the voltage to 500 volts and higher, it then stores the voltage in the ignition’s capacitor. Once it receives a trigger signal it will then slam the coil with this voltage and the outcome is a current that could reach the 30,000 to 45,000-volt range. The result is more heat in the cylinder which creates improved combustion.

Multi-Spark Ignition Systems like the Street Fire CDI Ignition will deliver a series of sparks during low RPM to create great throttle response and a smooth idle.


Because the voltage is so high with CD ignitions, the spark has a tendency to be very short in duration. This is an advantage at high RPM, however, at lower RPM, MSD explained to us that it has the possibility to create problems. Because the spark is so short in duration the result can be a very rough idle. So to combat this, ignition companies started firing the plug multiple times in the same cycle. “Most CD ignitions create multiple sparks when the engine is below 3,000 to 3,300 rpm,” Ryden told us. “As RPM drops, an increasing number of sparks occur because there is more time to fire the plug.”

This means at idle there could be 5-6 sparks occurring within the same cycle. This helps create better throttle response and a smooth idle.

How A Rev Limiter Works

A rev limiter works by using a module or a switch on the ignition that will hold the RPM at the desired limit.

With many high performance CD and even some inductive ignition systems, comes the ability to limit the RPM’s of the engine by working with a rev limiter. This can be a valuable resource for those that want to protect their investment.

Many think of the rev limiter as a way to simply keep the RPM from exceeding a certain point. But in reality the rev limiters also protect us from ourselves. Whether it is a missed shift or a sudden spinning of the tires, the rev limiter could save you thousands of costly repairs from your simple mistake.

A rev limiter works by using a module or a switch on the ignition that will hold the RPM at a desired limit. It does this by monitoring the engine’s RPM and once it reaches the limit it will drop the sparks to different cylinders in order to hold the RPM at the given limit. Most rev limiters either choose the cylinders at random or by dropping the sparks in a set pattern.


Ignition systems, while extremely complex, are something that can be understood.  Don’t be afraid to do a little research, ask the experts like we did, and get your hands dirty in your ignition system. Trust us — there’s power to be found in those wires!

About the author

John Gibson

John has been around dirt track racing his entire life. In fact, he was almost born at Monett Speedway in Monett, Missouri. He has raced everything on dirt and asphalt from karts, to Indy cars, to 650 horsepower stock cars in the USAR Pro Cup where he currently races.
Read My Articles

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