MSD Top Ten Ignition Questions Tech Bulletin - Manual (Page 2)

idle, 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
fire 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.
3. What is the best spark plug gap for my application?
The spark plug is the point in the ignition system where electrical energy is converted into heat, consequently, the
larger the gap the greater the amount of heat available to light the air/fuel mixture. However, too large of gap com-
bined with increased cylinder pressures can put excessive pressures on the initial voltage needed to ionize (cross)
the gap. Finding the optimum plug gap for your application is best determined by experimentation because there are
so many engine variables to consider.
An MSD Ignition Control has enough output power to consistently fire wider spark plug gaps on a performance
engine. As a starting point, follow the engine builder or manufacturer’s recommendation for the plug gap. With that,
you can experiment with increasing the gap until the best performance is found.
As a rule of thumb, it is recommended to increase the plug gap by .005” - .010” followed by testing and tuning.
Keep in mind that larger spark plug gaps also place increasing demands on the secondary portion of the ignition
system including the distributor cap and rotor, coil wire, and spark plug wires. They should all be in top condition and
checked periodically during the race season. Remember that electricity takes the path of least resistance to a ground
so if the gap is too large the spark may short to another point with less resistance.
4. What size battery do I need if using an MSD ignition?
The battery is the fuel tank for the ignition system (magnetos excluded). When it’s empty there is no electrical power
available for the ignition system to convert into heat at the plug gap. In long duration racing events such as circle
track racing, an alternator is highly recommended. In drag racing, a charging system is not a complete necessity as
long as you have a good battery and charge it in between each round. Also keep in mind that electric fuel and water
pumps, fans and solenoids eat up a lot of current as well.
Race cars without charging systems must have a battery with a large enough capacity to power all the electrical
parts. For example, an MSD 6 or 7 series ignition consumes approximately one amp per thousand rpm, so at 5,000
rpm the MSD alone is using five amps. An MSD is designed to produce full power sparks with a supply voltage of
10 volts, but if the supply drops below that, ignition output will suffer.
An MSD can be used with 16 volt batteries, but no performance gain will occur because the output power of the
MSD is regulated. The advantage of a 16 volt battery is increased electrical capacity. For more information on battery
requirements with an MSD, ask your MSD Customer Support Tech for our Battery Tech Bulletin.
5. What do you have to replace my points distributor and what are
the advantages with electronic versus points?
MSD does not have a module to replace the breaker points system in your stock distributor, however an MSD Igni-
tion Control will work great with a points trigger ignition. In fact, if you replace the points when you install your MSD,
you’ll probably won’t have to replace or adjust them for years!
The MSD’s trigger wire connects directly to the breaker points wire so when the points open, the MSD is triggered.
Since the MSD’s capacitor is responsible for sending the spark energy to the coil, the points are only used as a trigger
reference signal. With this connection there is very little current crossing the points so the wear is nominal at best.
Also, the MSD controls the dwell so the adjustment of the points is not that critical either. This setup works great with
street cars and budget racers, but when you begin stepping up performance more and more, the need for a quality
distributor comes into play.
MSD’s Pro-Billet Distributors are engineered to deliver precise trigger signals, provide accurate distribution of the
sparks and are reliable. A magnetic pickup is used to trigger the ignition. Unlike points, this pickup is maintenance-
free and is capable of accurate trigger signals throughout 10,000 rpm.
6. What is the best Timing Curve for my car?
There is no real way for our Techs to answer this question but they can point you in the right direction. It takes
testing and tuning time to find the best curve that fits your application. Many variables affect the ignition timing curve
such as compression, cam specs, intake system, fuel, exhaust, altitude, driving habits and so on. The chart on page
3 lists some factors that will help you determine what sort of timing curve you should work towards for your specific
application.
MSD’s mechanical advance mechanism is accurate and easy to adjust so you can try different combinations with
the supplied springs and stop bushings. We also offer a variety of electronic timing controls so engines with locked
out timing or crank triggers can take advantage of altering the timing as rpm changes.
Note: When you are testing different curves, listen for detonation (spark knock) which is a sign of over-advanced timing.
7. Tach Adapters; What are they and why do I need one?
MSD’s Tach Adapters are solutions to two problems that may occur in a few applications after installing an MSD
Ignition. They will modify the tach signal of the MSD so tachs that have trouble picking up the MSD’s signal and on
select import vehicles with fuel injection systems, they will boost the signal so the ECU can trigger the EFI.
Some tachometers, original equipment and aftermarket, may have trouble reading the MSD’s tach signal causing
erratic readings or just not working. An MSD Tach Adapter modifies the tach signal so these tachometers can read
them correctly. MSD lists different tachs and applications that may require an Adapter in our catalog and the Ignition
Control Instructions.
Some import vehicles may experience a no run situation after installing an MSD. This is because some systems
use the same trigger source to operate the ignition and the fuel injection. When the MSD is installed this voltage
signal becomes too low to accurately trigger the fuel injection. The PN 8910 Tach Adapter will usually remedy this
problem. Ford Probes and Toyotas require a special Adapter that can be ordered directly from MSD.
If you experience any of these problems after installing your MSD, contact our Customer Support Department for
more information on your application.
8. How do I fix:
• A high rpm miss when the engine is under load?
• An rpm limiter that seems to activate at the wrong rpm?
• Erratic operation of electronic devices/ECUs?
• A tachometer needle that seems to “bounce”?
All of the above can be caused by Electro Magnetic Interference (EMI) generated by the ignition system. Specifi-
cally through the coil and spark plug wires. The ignition system is a miniature power station and the spark plug wires
are its transmission lines. The wires (in particular, “solid core” wires) can broadcast EMI that seeps into electronics
and causes erratic behavior.
To combat EMI you need to run a set of helically wound spark plug wires such as MSD’s Heli-Core or 8.5mm Su-
per Conductor Wires. Having the conductor wound around a special center core produces a “choke” that holds EMI
inside the wire. Solid core wires on the other hand, have no suppression capabilities and should not be used with
an MSD Ignition. MSD’s Super Conductor Wires have extremely low resistance (less than 50 ohms per foot), yet are
designed to suppress EMI like a high resistance wire.
A variety of timing curves can be achieved with MSD’s mechanical advance.
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