Mancini racing spark plug chart

Mancini racing spark plug chart DEFAULT

Autolite Copper Core Spark Plug


14mm Thread, .375 in. Reach, Projected Tip

Spark Plug, Copper Core, Gasket Seat, 14mm Thread, .375 in. Reach, Projected Tip, Resistor, Each

Shorty Spark Plug: No

Resistor: Yes

Manufacturer Heat Range: 5

Electrode Core Material: Copper

Electrode Tip Material: Copper

Insulator Type: Projected

Spark Plug Thread Size: 14mm

Spark Plug Reach: 0.375 in.

Spark Plug Seat Style: Gasket

Wrench Diameter: 13/16 in.

Ground Strap Quantity: One

Quantity: Sold individually.

These Autolite copper core spark plugs feature a cold-formed steel shell with precision-rolled threads, a full copper core electrode to provide better performance, and a one-piece terminal post to add strength. Autolite copper core spark plugs use a copper-glass seal that bonds the insulator and terminal post center electrode together. This ensures full voltage at the spark gap and a 100 percent leakproof, gas-tight seal. Autolite features an extensive application guide to cover just about everything with an internal combustion engine. Keep your engine running smoothly and reliably, simply by switching to some new Autolite copper core spark plugs.


NGK Racing Spark Plug


14mm Thread, .375 in. Reach

Spark Plug, Racing, Gasket Seat, 14mm Thread, .375 in. Reach, Projected Tip, Non-Resistor, Each

Shorty Spark Plug: No

Resistor: No

Manufacturer Heat Range: 5

Electrode Core Material: Copper

Electrode Tip Material: Nickel alloy

Insulator Type: Projected

Spark Plug Thread Size: 14mm

Spark Plug Reach: 0.375 in.

Spark Plug Seat Style: Gasket

Wrench Diameter: 13/16 in.

Ground Strap Quantity: One

NGK Part Number: R5670-5

Quantity: Sold individually.

Notes: Motorcycle applications only.

What's firing your engine? NGK racing spark plugs are built to withstand the severe mechanical and thermal shock associated with high-revving, high-compression engines. NGK racing plugs feature electrode materials--precious metals like platinum or gold/palladium--for greater durability and low voltage requirements. Fine-wire center and ground electrodes provide better sparking and enhanced ignitability. And, the special arrangement of insulator noses improves throttle response! So, what's firing your race car to the winner's circle? Whether you're a weekend warrior or an expert racer, rocket your way to victory with racing spark plugs from NGK--the people who spark winners!

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How to Build Mopar Engines for Performance: Ignition System

Current aftermarket ignition systems and components offer significant benefits for A-engines. An A-engine needs to be converted from breaker point to electronic ignition system for any performance application. In essence, you optimize the ignition system so it effectively ignites the fuel charge in the combustion chamber. A max-performance engine typically intakes a larger fuel/ air charge and you need an upgraded system that’s correctly calibrated so the engine performs at its full potential.

This Tech Tip is From the Full Book, HOW TO BUILD SUPERCHARGED & TURBOCHARGED SMALL-BLOCK FORDS. For a comprehensive guide on this entire subject you can visit this link:


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The A-engine’s original breaker point and coil pack system is woefully inadequate for today’s max-performance engine. Therefore, you should convert to Mopar Performance, MSD, Accel, or another modern electronic ignition system.

Magnum engines are unique and the ignition is part of the computer. The ignition system is everything that is required to ignite the air/ fuel mixture inside the combustion chambers of the engine. These ignition parts are distributor, spark plugs, plug wires, control box or ECU (electronic control unit), coil, ballast resistor, switches, wiring, battery, starter, ground straps, voltage regulator, and a few odds and ends.

With the introduction of fuel injection (MPI) with the 1992 Magnum 5.2L engine, an ECM replaced the ECU,  and an additional six or seven sensors were added to the system.

Spark Advance

To make maximum torque and horsepower, the spark plug must fire at a specific moment relative to the crank and piston. A chart or graph of this event relative to engine speed is generally called a spark advance curve. Spark advance is much more critical on street engines or street/ strip engines because they use the full range of engine speeds and loads; race engines tend to run at high speeds and a fixed advance.

In general the total spark advance curve has three phases: initial, centrifugal, and total. Initial advance is the number that you set with a timing light by rotating the distributor housing while the engine is idling at low speed. The distributor has a mechanism inside the housing that provides centrifugal advance, which changes with the engine speed (RPM).

The sum of the initial advance and the centrifugal advance is called the total advance. For racing applications you set the total advance rather than the initial advance. If the spark advance is graphed or plotted against the engine speed or RPM, the resulting graph is called the spark advance curve.

Another type of advance is vacuum advance, which is an add-on advance. A pot attached to the side of the distributor creates the vacuum advance. It is driven by engine vacuum, a small vacuum line runs to the end of the pot from the bottom of the carburetor. It is very important to a true street car but is often disconnected (plugged) for racing.

For example, assume that your distributor has 22 degrees of centrifugal advance built into the advance mechanism. If you set an initial advance of 10 degrees, you have a total advance of 32 degrees (10 + 22 = 32). If you increase the initial advance to 13 degrees, your total advance becomes 35 degrees (13 + 22 = 35).

Vacuum advance is an add-on, so if you have 15 inches of vacuum at cruising speed (freeway), total advance at this RPM (maybe 1,800 rpm) might be 25 degrees (13 initial plus about half of the centrifugal) plus the 15 degrees of vacuum advance for 40 degrees at cruising speed, which results in better fuel economy. If you go to wide-open-throttle, the vacuum drops to zero and the vacuum advance also drops to zero. It’s back to 25 until the RPM changes. But I’m getting ahead of myself. To discuss the ignition system for street and performance applications you have to know what spark advance is. The actual advance curve is controlled by the internals of the distributor (or the computer in Magnum engines).

When selecting an ignition system, the standard Chrysler electronic system offers the best bang-for- the-buck. Period. Once you have the basic electronic distributor you have many options. I favor Chrysler ignition boxes. The orange box is set up for the street and the chrome box is for the street/strip engine.

MSD 6 is probably the most popular option for the street/strip. MSD 7 is the race ignition and the high-RPM ignition (7,500 rpm and up), but it is not required for the street/strip application in most cases. For the street/strip engine, I favor an MSD Blaster coil.

Performance ignition manufacturers offer three kinds of conversion kits: one for the standard engines, aimed at general street engines (based around a vacuum-advance distributor), and one for racing engines that was based around a race distributor (faster advance, or fixed advance, maybe billet, and sometimes mechanical tach drive features in the distributor) and an upgraded race ECU (higher RPM and more energy).

Magnum engines have computer- controlled ignition, but some customers prefer to adjust the ignition  themselves. If you want distributor adjustment in your Magnum engine, the  solid-shaft distributor must be replaced. The electronic conversion kit (Mopar Performance) is the easiest way to get the hardware you need for the new electronic distributor.


A-engines used rear distributors; Magnum engines used solid-shaft distributors with the advance hardware built into the computer or ECM. The exception is the Lean-Burn package built in the mid-1970s that also used a solid-shaft distributor.

Vacuum Advance for A-Engine

For many years the standard production A-engine distributor has been equipped with the vacuum-advance electronic hardware and also served as the basis for the standard performance distributor. The housing is made of aluminum so it is very lightweight. The vacuum-advance pot is mounted to the outside of the housing; it is the easiest way to identify one of these distributors.

There have been many versions over the years. Most are based on the advance curve, which is directly related to the springs in the advance mechanism. Production used two springs: one light and one heavy (with a loop in the end). Performance distributors had one spring, or two light springs, and the performance advance curve was fully advanced by 2,000 rpm. The vacuum-advance pot is on the outside of the housing and has an arm that reaches inside and attaches to the advance mechanism. The vacuum does nothing if the vacuum hose is not attached. The typical vacuum source is the carburetor. It is good for street engines because it is an add-on advance, which helps increase fuel economy in high-vacuum situations.

Billet Distributor

Most billet distributors are basically electronic distributors where the main housing is made by CNC-milling a block of aluminum. MSD now makes a billet distributor with the advance mechanism on top of the reluctor, which allows easy access. MSD has plotted out six different advance curves (slow to fast) based on color-coded springs and amounts of total centrifugal advance ranging from 18 to 28 degrees. Because it is just inside the cap, it is easy to make adjustments and doesn’t require a distributor machine.

These MSD, Accel, and Crane billet distributors are nice but somewhat expensive. The standard electronic distributor is for the street/strip. One interesting approach is the new MSD adjustable mechanical-advance billet distributor. Another new possible solution is the MSD E-curve billet distributor, which has a program inside the distributor, easily accessed on the outside of the housing, that changes the advance curve.

Crank Trigger

On a V-8 engine, only four blips are needed because the crank rotates at twice the cam speed. Part of the system is a bracket that is added to the front of the engine designed to hold the triggering sensor(s). This bracket is designed with timing adjustment capability. Typically the system uses two pick-ups for a racing engine: one for starting and one for actual running.

Cap and Rotor

Vacuum-advance-style, mechanical tach/billets are built for the Chrysler electronic ignition distributors; the Magnum type fits only the newer Magnum computer distributors.

The vacuum-advance distributor has a notch in the bottom lip of the cap at the clip location. The mechanical tach version has a small tab that protrudes from the lower lip of the cap, and the bracket that holds the cap on has points that the tab centers in. The Magnum version is the easiest to spot because it has spark plug ends in the terminals and two small screws where the spring clips are normally located. The first two electronic distributors used two spring clips to hold the cap onto the main housing. The two caps are not interchangeable.

Accel services caps for both Chrysler electronic distributors. MSD services the caps for their distributors, which use Magnum-style terminals in the cap.

Aftermarket Ignition Systems

If you’re running a mild street engine that does not rev above 5,500 rpm and runs less than 9:1 compression, a stock ignition performs well. If you’re building a 500-hp or more powerful engine, you need an upgraded ignition system. Most max-performance builds have large-port aluminum heads, aggressive cams, and intakes and carbs; the OEM ignition (electronic) system (the box) was not designed to keep pace, so upgrade the box (orange or chrome) followed by upgrades to the coil, plug wires, and plugs (colder). If you don’t, your engine won’t perform to its potential. In the final analysis, if your engine does not provide strong enough spark for the fuel charge, you’re wasting potential performance.

Mopar Performance, MSD, Accel, and PerTronix offer complete high-performance ignition systems for A-engines, and they offer components for almost every application, whether it’s street, street/strip, or race. When building a max-performance, you should select a complete aftermarket ignition system as a kit or select the components that complement one another. As such, you should buy a distributor, ignition box, coil pack, and spark plug wires from a single manufacturer that work as an integrated system. Although you can mix the components from various manufacturers, often there is no performance gain to be realized, and then you have to verify that all components are compatible.


PerTronix has long been one of the leading aftermarket manufacturers of high-performance ignition systems. The company makes a wide range of distributors, digital CD boxes, coils, and wires that are suitable for A-engine small-blocks.

Made of CNC-machined 6061 T6 billet aluminum housing, the PerTronix Flame-Thrower II distributor simply slides through the manifold and into the block. Attach a few wires and it’s ready to run; it works with any inductive ignition system coil, but high-RPM performance can be improved when it is used with the low-resistance (.6 ohm) Flame-Thrower II coil. You can use any multi-spark CD ignition box with the distributor.

The distributors can run up to 10,000 rpm, so they are tough. You need to select the coil that’s suited to your particular application, so PerTronix offers coils with different voltages. The Flame-Thrower II produces 45,000 volts, the Flame-Thrower HV supplies 60,000 volts, the Flamethrower III 45,000, and the Flame-Thrower HC throws out 60,000 volts.


Many engine builders select the Pro-Billet distributor, MSD 6 box, and Blaster coil for high-horsepower street engines or for street/strip. The Pro-Billet distributor is made of 6061 T6 billet aluminum, which is similar to the PerTronix, and both of these tough distributors are less prone to deflection. This plug-and-play distributor simply slides into the distributor shaft hole and you clamp it into position. The distributor can operate through 10,000 rpm, and it has an adjustable mechanical advance assembly that allows you to accurately set timing. In addition, you can easily modify the advance curve to match your specific application.

The MSD 6-Series provides strong spark energy and precisely controls ignition actuation, so if you’re building a max-performance engine of 500 hp or more, this box helps deliver strong throttle response and better overall performance. MSD offers several different versions of the MSD 6 box for almost any engine package.

Most engine builders start with the Digital 6AL box that’s designed for aggressive driving and some form of racing rather than the MSD AL-2 box, which is suited for street/ strip applications. This box has a programmable advance curve. The Extreme Duty 6 ALN is designed for racing applications. As with most engines, they are going to produce more power and high-ignition energy, greater combustion chamber temperature, and longer duration.

When using the billet distributor and the MSD 6 box, you should use the compatible MSD Blaster 2 coil. It  puts out 45,000 volts compared to 15,000 from a stock coil.

Mopar Performance The Mopar Performance electronic ignition kit (try Jeg’s or Mancini Racing as a source) features an aluminum vacuum-advance distributor, orange-box ECU, wiring harness, and ballast resistor. It is designed for street engines that operate at less than 6,000 rpm. Most shops find it offers the best performance for the dollar. I suggest using the MSD Blaster coil (see above) with this package.

For the street/strip package, just upgrade to the chrome-box ECU for higher RPM engines (about 7,500 rpm). For higher RPM and/or racing, upgrade the ECU to the MSD 7 and its compatible coil.

Advance Curve

Two small springs and two pivoting weights control the distributor’s advance curve. The two springs can be changed to change the curve, but this does not apply to the Magnum engines.

In general, the design functions by lighter springs allowing a faster advance curve. Re-curving the distributor (a popular performance trick) is basically changing the springs in the distributor. it is easy to change the springs, but it is more difficult to know what the new curve is, and a distributor machine spins the distributor up to speed and shows you what the new curve is. Distributor machines are difficult to find today; one source is Koffel’s Place.

Ignition Timing

In most cases, Chrysler/Mopar small-block engines run best at 35-degrees total spark advance (the sum of the initial advance and the centrifugal advance). Because vacuum goes to zero at wide open throttle (WOT), it is not involved in this area of performance.

As a general guide, street performance distributors (vacuum) were fully advanced by 2,000 rpm; the race distributor was fully advanced by 1,500 rpm and also had a flat curve. The crank trigger was fully advanced after it started and also had a flat curve.


Basically the Magnum needs the same advance curve as the A-engine. It also needs the same total advance except that it is accomplished in the computer and therefore the computer must be reprogrammed (by SCT, for example) or another computer added (such as from AEM or FAST). The HP A-engine has too much spark at 2,000 rpm, but it is not as big a concern on Magnum engines as long as the ECM is not “pushed” into the 2,000-rpm area. Six sensors help with fuel octane and load issues.

Spark Plugs

The job of the engine’s spark plugs is to ignite the fuel/air mixture that is in the combustion chamber. This somewhat straightforward job becomes more difficult as the engine’s output (torque and horsepower) and speed (RPM) increase. Production A-engines have had 3/4-inch-reach plugs for 2-barrel engines, 4-barrel engines, and high-performance engines, so the range is greater than you might expect. Magnums use one plug. In plug lingo, the A-engine used standard plugs and the Magnum used a resistor-type plug.


Magnum plugs use a gap of .040 inch. A-engine plugs use a basic gap of .035 inch. Wider gaps can be used with certain high-energy electronic ignition systems.

Mopar/Chrysler tested plug gaps with race ignitions as high as .050 to .060 inch. If the ignition is up to it, the wider gaps (maybe .040 for the A-engine and .045 for the Magnum) go faster, but the .035- to .040-inch gaps are more durable.

Street Plugs

The N12Y and the RC12LC4 plugs are a place to start in general. If more racing is expected, colder versions are recommended. I would also push the gap to .040 to .045 inch. Spark plug installation torque is as follows: cast-iron head, 26 to 30 ft-lbs; aluminum head, 18 to 22.

All Magnum engines use a heat shield around each plug. The shield can be removed with a pair of channel lock pliers. The gap in the heat shield should be pointing upward.

Plug Wires

Production A-engine and Magnum wires are 7 mm in diameter. Try to keep the cable that runs from the coil to the distributor as short as possible. The wires are not interchangeable between the two because the distributor caps use different terminals.

For street applications and higher-energy ignitions systems, I recommend 7.5-mm pre-made plug wires from Mopar, Accel, etc. For the street/strip engine, I prefer the 7.5-mm pre-made plug wires offered by Mopar Performance or the 8-mm pre-made wires from Accel, Moroso, MSD, and Taylor.

For racing engines, consider 8 mm or higher. Moroso makes an 11-mm wire, Taylor makes a 10.4-mm wire, MSD and Accel offer 8.5-mm or larger wire. The large-diameter wires are designed for racing engines.

Suppression and solid-core spark plug wires are offered. Solid-core (metal) wires should only be used on race engines. Suppression wires provide protection from radio frequency emissions from the ignition system, which may be more important with the computers and electronics that are found on today’s cars.

Distributor Drive

The intermediate shaft drives the distributor, and it also drives the oil pump. The tab on the bottom of the distributor’s main shaft fits into a slot in the top of the intermediate shaft (installation of the intermediate shaft is discussed in Chapter 9). For performance engines, I recommend the race shaft because it has a pinned gear and that feature is very important to the ignition.

The aluminum-block sprint car engine uses a special distributor/magneto that has the drive gear and pilot attached to the distributor (all one piece) because the aluminum block does not use an intermediate shaft. It is designed for use with a dry-sump oiling system; therefore the standard oil pump is not used and leads to the intermediate shaft going away.

If you have a new block, make sure that you have a distributor drive bushing pressed into the block. If it is a used block, assume that you should replace it. This bushing is the last place you want oil and it takes a beating in high-mileage applications. (Chapter 1 discusses how to measure bushing wear.)

Coil and Ballast Resistor

The ignition coil and the ballast resistor need to work as an integrated system. Although the standard production coil has adequate performance with a CD box, you have a much hotter spark when using it with a booster coil. It works fine if you switch from a points ignition to an electronic (coils are not generally included in electronic ignition kits). The production coil is fine for general street use but there are upgrades.

The ignition system is also a factor and must be considered part of the team. For a general street performance upgrade, use an MSD Blaster coil for your application. Some race ignitions, such as the MSD 7, require special coils; do not mix-and-match.

Of the many coil specifications, but voltage tends to be the most popular, ranging from 34,000 to 55,000 volts. Coils are also rated on amperage, which varies from 140 ma to 2.0 amps, and spark duration, which varies from 200 to 350 us.


Electronic ignition offers many advantages over the basic points ignition. Here, I focus on electronic-style ignitions. These ignitions use a control box called the ECU. Magnum engines use a computer ignition controller called an ECM.

ECU for A-Engines

Mopar offers three levels of performance ECUs: orange (street), chrome (street/strip), and gold (race). The orange unit is good for about 6,000 rpm. The chrome units offer more performance with RPM up to 7,500. The gold box is good for more than 8,000 rpm. The black production unit is good for about 5,000 to 5,500 rpm.

ECM  for Magnum Engines

The ECM (or PCM, power control module) is different for every model in each year. The two-wheel-drive unit is different from the four-wheel-drive unit, the 5.2L is different from the 5.9L, the automatic transmission is different from the manual transmission, and a 1994 is different from a 1996. It seems crazy and is very confusing.

The ECM controls all ignition systems, such as total spark advance, initial spark advance, advance curve, and any vacuum advance that may be part of the map. For any performance upgrade, the computer (directed by the ECM) must be reprogrammed. Mopar Performance offers a few high-performance ECMs, but models are very limited, so I do not recommend them.

Chrysler/Mopar Performance computers are great for street vehicles and fully compliant with CARB emissions standards, but they are difficult to find. Certain years can be reprogrammed.

You may also want an overlay computer by AEM, FAST, or SCT. This second computer modifies the original program and also offers other options for more performance, but the production computer still operates the car’s electronics. Although products continue to change and evolve, AEM, FAST, or SCT are the best sources for Magnums and A-engines.

Aftermarket performance ECMs filled the void, but the OEMs didn’t want to give out their programming information, so each company solved the problem in their own way. The SCT original approach was to reprogram the Chrysler computer, basically the same as Mopar Performance did. Today, SCT offers reprogramming services but uses a supplemental hand-held device that reprograms the engine’s ECM; the customer can select one of several curves for added performance.

The FAST people took a different route but have devices that work with the factory ECM and piggyback to adjust the performance curves. The MSD system appears similar to the FAST system. The original AEM system (programmable ECM) basically replaced the original factory ECM. The new units seem to be moving toward the SCT approach where the new unit works with and overrides or reprograms the factory ECM.

The initial settings (centrifugal and vacuum) are the primary parts in typical electronic ignition system components. The ECM performs these functions on Magnum engines. The crank sensor is bolted to the back of the block and reads the engine’s TDC position through slots (windows) in the flexplate, which is inside the bellhousing. The sensor then sends the signal to the ECM. This means that the distributor no longer adjusts the engine’s timing. If you try to advance the distributor by rotating it for more advance, the computer knows and resets the timing to what is in its program. That is why you have to have the computer reprogrammed if you want a performance upgrade.

For racing applications, an MSD 6 or MSD 7 is typically used (A-engine). Another option is one of the digital ignitions mentioned above. On the Magnum side, AEM or FAST are two of the most popular ignition systems for these engines.


Most aftermarket ignition kits come with their own wiring, as did the electronic ignition kit. It was originally a five-wire harness, but that was updated to a four-wire harness.

Written by Larry Shepard and Posted with Permission of CarTechBooks



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Filed Under: Mopar Tech Tips

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