Classic Inlines
603 W Pecos Ave
Mesa, AZ 85210

Pertronix, Duraspark, or DUI ?

If you don't already know, there are numerous advantages to swapping out your old stock points style distributor for an electronic ignition system. In our opinion, regardless if you have a stock motor or a high performance rebuild, it's number one on the list for "Best Bang for the Buck". However, with so many choices available, it's difficult to know which system to choose. As such, we decided to compile the following information so you can make an informed decision when the time comes.

Basically you have three choices, a Pertronix, a Duraspark, or the DUI. While the Pertronix and DUI are pretty straight forward, the Duraspark has several options for an ignition source, which we'll explain later in he article.

  • Increases horsepower
  • Improves fuel economy
  • Reduces emissions
  • Lowers maintenance
  • Cleaner spark plugs
  • Quicker starts
  • Improved idle quality
  • Better throttle response
  • Eliminates flat spots
  • Quicker/Faster revs

Each system has a unique advantages over the other two. As such, it may be more desirable to install one system, as opposed to the other two, to better suit your needs. For example, the Pertronix is perfectly suited to a concours restoration, as it is completely hidden under the stock distributor cap, however it offers the lowest gains in performance. A nice feature about the Duraspark is that it can be installed on a tight budget, then up-graded when your budget allows. However it's the most difficult to install. Depending on the ignition box you choose, the wiring can be complex and confusing for some. On the other hand, the Pertronix and DUI are very easy to install. The DUI offers superior performance and the highest horse power gains, but it's also the most expensive system of the three, at least in terms of up-front cost. Which we'll explain later.

PERTRONIX: If you need to maintain the stock ignition system, say for a concours restoration, then a Pertronix ignition module is the only way to go. The Pertronix module is installed where the points use to be, so it is easy install and completely hidden under the stock distributor cap, there-by maintaining a stock appearance. Pertronix also offers 7mm spark plug wires to improve performance, yet they too maintain a completely stock looking appearance. The Pertronix Ignition modules are a great product for those working on a contours restoration, however we believe they have two major drawbacks. First and foremost, most conventional distributors, like the Duraspark and DUI, use mechanical advance (centrifugal weights in the distributor) to compensate for changes in rpm, which immediately swing out when rpm's are increased. Whereas the stock "Load-O-Matic" distributors (60-67) use venturi vacuum and a vacuum canister, which reacts slowly to the relatively weak venturi vacuum signal. As such, the "Load-O-Matic" distributors are very slow to provide spark advance when the engine is accelerated under load, and they are notorious for soggy acceleration. The stock and/or rebuilt Load-O-Matic distributors also use a single upper busing to support the distributor shaft, and like everything else, they wear out over time. When the bushing wears out the rotor begins to wobble, causing spark scatter and fluctuations in ignition timing. Therefore, while the Pertronix module increases spark quality, your still stuck with the poor operation of the "Load-O-Matic" distributor. Another thing to consider, six-cylinder Pertronix Ignition modules are usually a special order item, since most parts stores only carry Pertronix modules for V8 applications. Therefore we suggest keeping a backup module, or extra set of points, in your toolbox or glove compartment in the event of an unexpected failure. For more information, please read our tech articles on the Pertronix Ignitor, and the Load-O-Matic Distributor, which explains both items in greater detail.

DURASPARK: If a contours appearance isn't an issue, yet you want a dizzy that looks somewhat stock, the Duraspark II might be your best choice. Not only is the Duraspark II an excellent ignition source for those on a tight budget, it can be upgraded at any time. Most inline enthusiast prefer to run the DSII with either the Dyna Module (available from Classic Inlines), the MSD-6A (without rev limiter) or the MSD-6AL (with rev limiter). If your on a really tight budget, you can even build your own, using any 4 pin ignition module and a good heat sink. The biggest drawback to the Duraspark, is wiring and installation. Make sure you have the proper wiring diagram which is intended for your application, and that you know where every wire goes before you start. Check and double check the wiring, making sure it's right before you re-connect the battery cables. Failure to do so may cause an electrical fire, and/or damage to your electrical and/or ignition system. If your not sure, ask for help......

wiring diagram for the DSII with the stock Blue Strain ignition module

DUI: Like the Pertronix, the DUI is very easy to install, as it only requires one wire to a hot 12V supply. The most common way of doing this, is by running the hot wire from the distributor to the ignition switch. Or you can use a relay, which is the preferred method. Using the relay makes the wiring a little easier since you don't need to climb up under the dash or pull the instrument panel to get to the ignition switch.

stock wiring diagram

Never wire the DUI directly to the old hot wire without using a relay. The reason for this is simple. The old wire normally has a resistor somewhere in the line, which is usually behind the instrument panel. The resistor reduces voltage to the distributor, which in turn reduces performance. For the best results, you want a full 12 volts going to the distributor.

DUI without relay (by-pass required)

The resistor can be removed, or by-passed, but you won't need to worry about it if you use a relay. The relay uses the old hot wire (with or without the resistor) to trigger the relay, which then supplies a full 12 volts to the distributor via a NEW hot wire, which is ran directly to the battery.

DUI with relay (by-pass is optional)

For the ultimate in performance and spark intensity, you can install the optional Mini VIP, which is a small transformer that increases the voltage to a full 18V. The Mini VIP, which is installed in the new hot wire line, steps up the voltage to a full 18V, allowing you to open the spark plug gaps to a whopping .070". This provides a very intense spark that helps to keep your plugs clean, and in most cases allows you to run a richer mixture for increase performance and realistic gains of 10-30 horsepower over the stock ignition system.

Please see our tech section for more information on the Pertronix, Duraspark II, and DUI ignition systems, as well as installation and service tips.

stock - completely hidden
large cap - still looks stock
larger distributor & cap
Est HP Gains
1-5 HP
5-10 HP
10-20 HP
Custom Curved
Spark Gap
45-50 (65-70 with VIP)
upper only (see note #1)
upper only (see note #1)
upper & lower (note #1)
easy - two wires
complex - multiple wires
easy - one wire
Petronics II
n/a (stock dizzy)
$55-65 (with cap & rotor)
$350 (see note #2)
Ignition Module
$120 (Ignitor II)
$20-190+ (see note #3)
included (dyna module)
Coil - Voltage
$30-40 (40-45,000v)
$35-45 (45,000v)
included (50,000v)
Wire Harness
$15-120 (see note #4)
Total Cost
$110-320 (see note #3)
$350 (see note #2)
$20 (see note #4)
VIP 18V Booster
$250 (see note #5)
High Volt Coils
$45-120 (see note #6)
$45-120 (see note #6)
included (see note #6)
Plug Wires
various (see note #7)
various (see note #7)
$85 (see note #7)
module is special order
may be difficult to locate
readily available
$120 (Ignitor II)
$20-190 (see note #3)
$20-120 (see note #2)
$30-70 (40-60,000v)
$30-75 (45-51,000v)
$30-70 (45-50,000v)
Cap & Rotor
Cap Adaptor

The stock and/or rebuilt Load-O-Matic distributors only used a single upper busing to support the distributor shaft, and like everything else, they wear out over time and need to be replaced. Unfortunately this rarely happens. When the bushing wears out the rotor begins to wobble, causing spark scatter and fluctuations in ignition timing. To alleviate this problem, Performance Distributors' installs a full length oil impregnated brass bushing in the DUI Duraspark II Distributor to provide additional shaft stability, there-by ensuring accurate and precise timing and trouble free operation for years to come. Plus every DUI Duraspark II Distributor is set up and custom curved on a distributor machine, unlike the cheaper rebuilt distributors offered by your local parts store.
The DUI is based on the HEI design, which incorporates the module and coil inside the distributor cap. This makes the installation extremely clean and easy, requiring only one wire connected to a hot 12V source, such as the ignition switch. However to ensure a full 12V we recommend wiring the distributor directly to the battery via a 12V relay (see note #4). For maximum performance, you can install the optional VIP, which steps up the voltage to a full 18V (see note#5). While the DUI is the most expensive distributor up front, it offers the highest HP gains and lowest maintenance. When it come time to replace a burned out module, you can use any generic 4 pin module ($20), which are considerably cheaper than the Petronics or MSD ignition modules, or you can use any aftermarket 4 pin module offer by companies such as MSD, Mallory, Excel, and many others. However we recommend the original Dyna Module ($50), that came with the DUI, which is available from Classic Inlines. For more information, see our tech article.

There are many different ignition modules that can be used with the Duraspark II distributor, including the Ford "Blue Strain" Module ($40), any aftermarket module such as the commonly used "MSD6-AL" ($190), a digital ignition module such as the "MSD6-AL-2" ($280). You can also use Classic Inlines "Dyna Module" and "Inferno" coil ($115), or make your own using any 4 pin HEI module, heat sink, and coil. The main point we are trying to make here, is that the total cost of a DSII ignition system can vary greatly. While a budget ignition system can be put together for about a hundred bucks, a digital ignition box and matching coil can push the price up to $400 or more. However, most DSII installs run between $250-350, depending on the cost of the ignition module, coil, and wiring/harness. For more information, see our tech article.

Depending on which module you use with your Duraspark, you may be able to make the installation easier by purchasing a pre-made wire harness. For example, the Painless #30812 wire harness can be used to connect the DSII to an MSD6 ignition box. If you choose not to use a harness, or if one is not available, make sure you have a supply of wire connectors, splices, and electrical tape on hand. You'll also need the right wiring diagram for the ignition module you are using. For more information, see our tech article.
While the DUI can be wired to the ignition switch, we recommend wiring it directly to the battery via a 12V relay, as this ensures a full 12V being supplied to the distributor. The relay is then triggered by the ignition switch. The easiest way to do this, is to use the hot wire (+) that went to the old coil. For more information, see our tech article.
If you have a DUI ignition system, you can add the optional "Mini VIP", where a simple three wire hookup sends a sizzling 18 volts to your ignition system. Because electronic ignitions like voltage, the 18 volt output allows you to open the spark plug gaps to an astounding .070"-.075". The larger gap burns the fuel mixture more completely on each piston stroke, and in most cases allows you to re-jet the carburetor to run a richer fuel mixture. A richer fuel mixture translates into more horsepower! The higher voltage also helps to prevent the spark plugs from fouling out, which is common in the 3rd and 4th cylinders of an inline six.

Pertronix FlameThrower Coil - round body (40-45,000v) e-core (60,000v). Price range $30-75.
MSD Blaster/Blaster II Coil - round body (45,000v) or e-core (48,000v). Price range $30-60.
Mallory Street/Strip Coil - round body (51-58,000v) or e-core (51,000v). Price range $40-75.
DUI/HEI Performance Coil (in cap) - aftermarket (45-50,000v) $30-70 or DUI (50,000v) $50

We didn't list plug wires in the cost, as there are literally hundreds of choices with a huge range in pricing. While any of the three ignition systems can use your basic budget priced wire sets, I think one can assume that most up-graded ignition systems will include a good quality wire set. Those using the Ignitor ignition system may opt for Petronics "stock looking" 7mm plug wires ($40) to maintain the stock appearance. DSII owners commonly use 8mm wire sets that are manufactured by the same company that makes the ignition module and/or coil, such as MSD, Crane, Accel, or Ford Racing ($35-75). As for the DUI, most purchase the matching LiveWires ($85), or a high end plug wire such as MSD or Accel ($55-75). LiveWires differ from all other spiral core plug wires as they have a braided glass sleeve, which offers superior resistance to heat, moisture, and oil spills.

Written By:
AzCoupe - Fordsix forum admin and owner of Classic Inlines

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