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All About Mustang Spark Plugs and Ignition Components

By:  Josh Honeycutt  / May 29 2019
All About Mustang Spark Plugs and Ignition Components

The ignition system on your Mustang can be affecting more than you know. Keeping everything up to par or upgrading to aftermarket parts can have an impact on power, mpg, as well as throttle response. A hot topic of conversation is how to choose the right plug for your Mustang. Answering this question requires a bit of knowledge about the plugs you're currently using, as well as the performance level of the car. When finding the best plug for your application, there are a few things you'll need to consider.

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Facts About the Mustang Ignition System

  • Factory plugs are used for their durability and emissions qualities
  • Copper inner cores are great for conducting electricity and used in most plugs
  • Proper heat range is important to remember while choosing a spark plug. Colder plugs are recommended for force induction applications to prevent detonation
  • Heat ranges are marked by the plug’s serial number
  • Heat range dictates the plug’s best operating temperature and heat resistance
  • The heat range is based on the insulator nose in the plug
  • A larger spark plug gap is desired in a naturally aspirated Mustang, but a smaller gap is desired in a forced induction engine
  • Spark plug electrodes are made using iridium, platinum, silver, and gold. The harder the material, the more punishment they can take
  • The center electrodes or tips come grooved so the spark is more centered for more efficient combustion
  • Coil-on-plug setups provide a hotter spark for a more efficient burn
  • Upgraded coil packs can lead to better throttle response
  • Resistance in plug wires can hamper the strength of the spark
  • High performance ignition coils can stabilize idle

Spark Plug Overview & Gapping

The spark plug gap is the area between the ground strap and the electrode. This is where the spark jumps from the electrode to run to ground, lighting the air-fuel mixture in the combustion chamber. In naturally aspirated Mustangs, a larger gap is desirable as it provides a “fatter” spark. In forced induction engines, the opposite is true. The gap must be reduced because of the increased turbulence and pressure in the combustion chamber. If not, the spark could be blown out causing a misfire.

Ford rolled the stock 4.6 engines out with Motorcraft platinum tip spark plugs. These plugs are gapped from Ford’s factory at .053 inches. The stock range can be from .049-.053, but anything past that will need adjustment. In recent years, many aftermarket companies have researched and developed better spark plugs. These plugs allow for a more complete and efficient burn. 

Consult the chart below for appropriate gaps for your model year. Gaps for boost are for psi between 10-15. For those of you running 17 psi or more, you will want to have a smaller gap. The main goal is to have the largest gap possible without having spark blow out. Always start with the largest gap setting and work down.

Gen Stock Boosted
1979-1993 (Foxbodies) 0.049-0.054 0.028-0.034
1994-2004 (New Edge and SN95) 0.052-0.055 0.032-0.035
2005-early 2006 (S197) 0.040-0.050 0.032-0.035
Late 2006-2010 (S197) 0.052-0.056 0.032-0.035
2011-2018 (Coyote engine) 0.049-0.053 0.028-0.032
2015-current (EcoBoost) 0.028  

Are the Factory Spark Plugs Good?

The factory plug was mainly used because of its durability and emissions qualities. Ford was required to hit 50,000 miles for the emissions warranty as dictated by the federal government. The factory plugs work quite well on stock and mildly modified cars. However, there are some gains to be made through the aftermarket. There are also situations where plugs with different heat ranges are needed.

OEM level plugs will help you regain the lost power that has slowly disappeared from your engine. They’re great for stock engines and lightly modified engines. Ford Motorcraft makes a great replacement OEM spark plug that will help to restore the lost horses.

Motorcraft 2005-2008 GT Mustang OEM Spark Plug
2005-2008 GT OEM Spark Plug

Spark Plug Core Types

The first myth that needs to be debunked is in regards to spark plug electrode type. All automotive spark plugs have a copper core. Or to be on the safe side, 99.9% of all automotive spark plugs utilize a copper core. Whether you’re looking at a set of OEM cheapies or the top-dollar Super Power Performance Plugs, both have the same element at their respective cores, and that element is copper. Now why would a set of $20 plugs versus a set of $60 plugs use the same stuff down under? Well, quite simply, copper is exceptional stuff to conduct electricity, promote jumping the gap and dissipate heat. There isn’t anything better readily available or cost-efficient.

However, the key word at play here is ‘electrode core’. Copper makes up the electrode core, but NOT the entire electrode itself. The electrode itself is composed of a core material (copper), and an outer electrode material. Spark plug manufacturers use varying outer electrode materials for different benefits, which we will look at next. So just to sum things up, when you see the term ‘copper’ thrown around, it is always referring to the inner electrode core, and the inner electrode core only.

OEM Ford Motorcraft Spark Plugs for 1999-2001 Cobras and the 2003-2004 Mach 1
Ford Motorcraft OEM Spark Plugs

Spark Plug Outer Electrodes

We now know all automotive spark plugs (really, we could broaden this statement to encompass all internal combustion engine spark plugs) employ copper as the core of their electrodes. So where do the crazy terms like ‘nickel-alloy’, ‘platinum’, and ‘iridium’ come from? Well, these materials are what encompasses​ the core, and are what make up the outer electrode. The first and foremost, nickel-alloy, is the usual material of choice for OEM spark plugs. It is the cheapest, and handles its duties without issue in stock motors. The subsequent two, platinum and iridium, are harder, more durable materials, able to withstand higher heat, with the latter being the hardest of them all (supposedly iridium is 6x as hard as platinum). When engines are modified out of stock parameters (i.e. more power), is when these harder materials will outlast basic nickel-alloy, ensuring a strong spark over a greater period of time, and under hotter conditions.

Number Four NGK Iridium Tip Close Up
Iridium NGK Plug Tip

Plug Tips

At the tip of the spark plug is the center electrode, where the spark is generated, and the ground electrode, where the spark jumps to. Conventionally, spark plugs have always had a concentric, flat tip, which work fine. However, several manufactures out there have started grooving their center electrodes so they are no longer flat (for example, NGK V-Groove means the center electrode has a v-shaped cut/groove, in the center of it). The concept behind this is simple. With a traditional flat tip, the spark is generated in the middle of the tip. With these grooved tips, the groove forces the spark to occur at the edge of the electrode, where manufacturers claim it is easier to ignite the fuel/air mixture, resulting in a better burn and requiring less voltage to produce the initial spark. MPG conscious vehicles often employ these types of plugs, where perfect ignition is another trick to boost efficiency.

The final tip mentioned, 15% tip, is the minimum you should tip for a service well rendered, say for a server at a restaurant. It isn’t automotive related, but it’s still a tip.

Autolite Spark Plug with a Flat Tip
Flat Tipped Spark Plug

What Does Heat Range Mean?

The heat range is the temperature at the tip of the spark plug electrode in a running engine. Think of it as the temperature at which the spark plug works best at, and how capable the plug is of resisting heat. The heat range does not affect the temperature of the combustion chamber directly. However, the heat from the combustion chamber can cause the temperature of the electrode to rise. Spark plugs with a lower heat range are set to be “colder” and vise-versa.

Certain plugs work better in cooler temperatures, whereas others are meant for a hotter application. It’s sort of like cooking a frozen pizza. Pizza A states it is optimal to cook it at 350C, and pizza B at 425C. Now, cooking pizza B at 350C will work too, but less effectively. The same applies to pizza A. Throwing pizza A in the oven at 425C again will work, but will probably burn if not vigilantly monitored.

The Importance of Proper Heat Range

It is important to choose a spark plug with the proper heat range for your Mustang. For example, with forced ​induction a “colder” spark plug should be used. This is due to the increase in pressure inside the combustion chambers. Using a spark plug with a higher heat range will cause detonation or “pinging”. This is also the case in high combustion engines.

Hot Range NGK Spark Plug
Hot NGK Plug

How Can I Identify a Spark Plug's Heat Range?

Most automotive spark plugs have a number indicating their heat range. As mentioned previously, this range of numbers signifies the spark plugs’ capability to resist heat. A ‘colder’ plug will not absorb heat to the same degree as a ‘hotter’ plug (meaning a ‘cold’ plug physically remains cooler than a ‘hotter’ plug). Thankfully, plugs are rated on a numeric scale to tell us which plug is hotter or colder than the next.

Unfortunately, each manufacturer uses their own range and description – there isn’t a standard across the board. For example, manufacturer NGK uses an inverse range from 2-11 to rate their plugs. The higher the heat range number, the more capable the spark plug is to withstanding heat, thereby it is a colder plug (meaning it remains cooler, it will not heat up as much). On the other hand, manufacturer Autolite uses an opposite rating system: the lower the number, the colder the plug (more resistant to heat).

What Makes a Spark Plug Hot or Cold?

What defines a cold plug and a hot plug is the length of their insulator nose. A shorter nose offers less surface area to absorb heat and a shorter path to dissipate heat to the cylinder head. A longer nose offers the opposite – greater surface area to absorb heat and a longer path to dissipate it—resulting in the firing tip to stay hotter. Furthermore, plugs with longer insulating noses have greater exposure to the gas igniting around the tip due to their greater length (they protrude further into the ignited gas). Other factors that may affect heat range can be composition material and their thermal conductivity characteristics.

Colder NGK Spark Plugs
Cold Set of NGK Plugs

When Should I Change My Spark Plug's Heat Range?

Changing heat range is for heavily modified NA cars or cars utilizing any type of forced induction. Any supercharger/turbocharger/nitrous setup will quickly generate more heat and a colder plug is necessary. With higher pressure comes greater heat, and thus, a colder plug is necessary. Usually moving one or two ranges colder is all that is necessary to combat the greater temperatures.

For minor NA builds it is usually not a necessity to change plugs. However, for swapping heads/camshaft(s)/building a new short block, changing heat ranges is not something to forget about. Major modifications require immense consideration and spark plugs are not exempt. There are many variables for determining a correct heat range ranging from compression ratio to engine load.

For stock Mustangs, the best plugs are stock plugs, which typically have a heat range of around 4-6, or whatever is midrange for the manufacturer in question (recall, manufacturers often use their own system).

Which Heat Range Spark Plug Should I Pick?

It is important to pick the right heat range for a multitude of reasons. First and foremost, the right plug will optimize spark, and consequently air/fuel ignition (remember, igniting the air fuel mixture is what makes power!). Secondly, it will ensure long plug life and reliability. A plug that does not reach its optimal operating temperature (running too cold a plug) will lead to carbon build up and poor performance. Running a plug that is too hot (does not stay cool enough) can lead to premature detonation in the combustion chamber, which can cause severe engine damage.

Do I Need to Retune for Hotter/Colder Plugs?

While running the correct heat range plugs for the tune it has is optimal, it is not essential to get a retune for them. Generally, if you have to change the heat range for spark plugs, there are modifications to the engine that mandate a retune.

Roush Supercharger Installed on a 2005-2010 GT Mustang
475 HP Roush Supercharger on a 2005-2010 GT

Aftermarket Options for Mustangs

NGK is one of the most popular aftermarket spark plug producers. They offer a great iridium spark plug for the mustang with noticeable gains in off idle throttle response. These can be picked up for around $70. The stock Ford Motorcraft plugs can be had for around $30. The E3 spark plugs resale for roughly $50 and use a nickel alloy electrode.

Brisk spark plugs rival those of NGK and offer great gains in off idle throttle response as well and come in at right around $80. Taking things to the extreme are Pulstar's Plasmacore spark plugs that use plasma- assited combustion and a nickel-chromium center for improved throttle response and fuel economy, coming in at around $120.

What Spark Plugs Should I Put in My Mustang?

Deciding on a plug comes down to your modifications, and what you plan on doing in the near future. With all the options out there, it’s easy to jump at the first spark plug with the most promises. However, the best spark plug is the one that suits your engine with the right heat range and gapped correctly.

Unfortunately, there's no easy way to determine which plug you get. It's a lot of trial and error, but here are a few things you should consider/watch for:

  • Combustion temperature/cylinder head temperature: if you raise the combustion/cylinder head temp (via forced induction, lean fuel mixtures, advanced ignition timing, etc.) you'll want a cooler heat range plug so you don't overheat the plug
  • If you're building a high RPM engine, you'll want a cooler plug (and vice versa)
  • If the plug is too cold (too much heat resistance) carbon deposits build up on the plug resulting in incomplete combustion
  • If the plug is too hot (not enough heat resistance) you'll experience pre-ignition and in extreme cases the plug will melt
  • Test a new set of plugs by inspecting them after a half-throttle, a 3/4 throttle, and a full throttle run
2015-2017 EcoBoost Mustang Brisk Silver Racing Spark Plugs
EcoBoost Silver Racing Plugs

Multi-Ground Spark Plug Pros and Cons

Are multi-ground spark plugs worth the money? Is there a short answer? No there really isn’t. Spark plugs seem like a simple component and it can be believed that a hotter plug is always the best choice when in reality too hot of a plug can be very harmful to the engine. 

If the engine creates boost or high compression you want to use something like a multi-ground spark plug because it will make sure all of the fuel and air is burned as closely to the time of ignition as possible. 

With a stock or low powered engine, using the stock plug type or one that is slightly higher is much more beneficial. Too hot of a plug in the right conditions can cause the engine to run as if it is running lean which can make the cylinder too hot leading to detonation issues.

When Should I Replace My Mustang's Spark Plugs?

Like tires and filters, a Mustang’s spark plugs degrade over time and should be replaced. It’s recommended to replace your old spark plugs every 30,000 to 60,000 miles. You can check your owner’s manual to review the recommended mileage for replacement. Spark plugs are often ​a forgotten about upgrade, but they can play a very important role in helping you to gain back any lost power and at a very reasonable price. If you want to provide your Mustang with a cleaner and more efficient spark, you should invest in some new plugs.

Keep in mind to never over torque your spark plugs. Most only require them to be hand tight, especially with anti-seize. Keep it between 10-15 ft-lbs.

NOTE: 2005-2010 GT Spark Plug Removal

The Ford 3 valve modular motors utilized a unique 2 piece style spark plug which has caused issues when removing the plugs from a high mileage vehicle as they are prone to cracking. The plugs look like this:

Used 2005-2010 GT Mustang Spark Plug Set
115K miles on 2006 GT Spark Plugs

Tools required: Ratchet with various sockets, spark plug socket, torque wrench set to 33 lb-ft, 10 inch extension, PB Blaster, air compressor with blow gun attachment

Step 1: Make sure the engine is COLD. Let it sit overnight if need be. Some people argue the engine should be warm, but when it's warm the aluminum of the head expands and makes the hole the plug sits in tighter. In a cold engine situation the aluminum has not made the hole tighter and the metal threats on the plug have not expanded either.

Step 2: Remove all plugs and ignition coils to access the spark plugs. Once removed take the blow gun and blow the debris out of the holes.

Step 3: Use your torque wrench with the extension and spark plug socket and try the plugs. DO NOT TORQUE THE PLUGS OVER 33 FT LB AND GO VERY SLOWLY. DO NOT USE AN IMPACT. If it will move, move the plug about 1/8-1/4 turn and stop. With luck, one or two of the plugs will come loose completely and you can remove it. 

Step 4: In the holes that still have the plugs in them, whether they were able to be partially turned or not, pour some PB Blaster, Seafoam deep creep, or some other penetrating fluid and let the plugs sit for 15-30 minutes.

Step 5: After waiting tighten the plugs back while not torquing over 33 ft lbs and then try loosening again. Repeat this process with stubborn plugs until they come out. DO NOT TRY AND FORCE A PLUG, IT WILL CRACK!

Step 6: Apply dielectric grease to top of plug and anti-seize to the threads if you want and reinstall plugs, again not torquing over 33 ft-lbs. Reinstall ignition coils and plug everything back in.

Check all connections of the ignition coils and injectors and start engine. Some smoke may come out from burning carbon buildup from the plugs and from the penetrating agent. If one of the plugs cracked, refer to Ford TSB 08-7-6 which illustrates how to use the motorcraft broken spark plug removal tool.

Complementary Modifications When Replacing Your Mustang’s Spark Plugs

When you’re on the hunt for that like-new spark your Mustang had right after rolling off the assembly line, doing a complete maintenance overhaul will provide the greatest gain that you are sure to feel. In other words, when you grab a new set of spark plugs, you should also plan on picking up some new coil-on plugs if you have a GT, Bullitt, or GT500. If you have a V6 Mustang, a coil pack and some wires will help you complement the spark. Coil Packs and Coil-on Plugs help produce more power for your motor.

1999-2014 Mustang Coil-on Plugs (05-14 GT, 07-14 GT500 & 11-14 V6)

On 2005-2014 GT Mustangs and 2007-2014 GT500’s and 2011-2014 V6 Mustangs, Ford used coil-on plugs rather than the coil pack that was traditionally used. Coil-on plugs are also found in the 1999-2004 Mustang GT, Cobra, 01 Bullitt and 2003-2004 Mach 1 Mustangs. When upgrading your ​coil-on plug with an Accel Super Coil-On Plug Kit, you can expect 10-15% more energy than the factory OEM coils. The coil-on plugs work simply by giving you a hotter spark. The hotter spark helps to burn the fuel better, creating more power and better fuel economy.

GMS 4v Hot Street Coil-on-Plug Pack for 1999-2004 Cobras and Mach 1 Mustangs

Mustang Coil Packs (96 - 98 4.6L, & 94 - 09 V6)

1996-1998 4.6L Mustangs and 1994-2009 V6 Mustangs all utilize coil packs in their ignition systems. We upgraded the coil pack on our 2000 V6 Mustang bolt-on build-up as well as our 2005 V6 bolt-on build-up using the Accel Super EDIS Coil Pack. Upgrading the coil pack gave us more power than the factory OEM coils could offer, which complemented our other mods and gave us peak performance and better throttle response.

1994-2009 Mustang Coil Pack

Mustang Ignition Coils

1994-1995 Mustang Ignition Coils: The 1994-1995 5.0L Mustangs use an ignition coil just like the Foxbody Mustangs, rather than the coil packs listed above, to help increase throttle response, idle quality, and starting power.

1983-1993 Mustang Ignition Coils: The Ignition Coil is found in the 1983-1995 5.0L Mustangs. Aftermarket ignition coils make more power than OEM factory coils to increase throttle response, idle quality, and starting power. It is a perfect match for stock engines and engines with minor performance upgrades.

Mustang Spark Plug Wires

Stock wires can become worn and cracked, which can cause them to slip off or even let water into the engine. When putting on new spark plug wires, you’ll be upgrading the actual wire itself, which features a low resistance conductor for minimum spark loss and more power.

When installing new spark plugs, it’s the best time to upgrade your other components as well. You’ll be removing your coil or coil pack and spark plug wires to access the spark plugs anyway. With a fresh system, you’ll be able to notice and feel your engine running better.

1999-2000 V6 Mustang with MSD Super Conductor 8.5mm Spark Plug Wires
8.5mm MSD Super Conductor Plug Wires

What About My Mustang's Battery?

A bad battery can cause a substantial amount of problems, although mostly minor. Without the battery, the engine can’t get started (unless you push start it). Like everything else, batteries are a mechanical item. They wear out overtime and need to be replaced. However, they can last much longer if properly maintained and cared for.

What Kind of Battery Maintenance are You Talking About?

Batteries have terminals, which cables connect to and distribute the power generated. These terminals, over time, can create battery acid. This battery acid can portray an insulator between the terminals and cables. If not cleaned, the battery can disconnect from the cables and create a weak connection or no connection at all. Cleaning these regularly (every few months is generally fine) can prevent connection issues and keep them strong. This can also relate to having an off-road vehicle for mudding. Mud can get into the engine bay and coat cables with dirt and grime. If a vehicle is taken off road where mud is extremely prevalent and driven into rather than avoided, it might be best to clean it after every session. 

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What Would Warrant a Battery Upgrade?

In stock form, with no modifications to the vehicle at all, there is really no need to upgrade anything. The stock setup works completely as designed when used with said design. However, there are modifications that can potentially require an upgrade. Upgrading the speaker systems (subs, better amp, head unit, etc.) can draw more power than the battery (and alternator) can provide. Upgrading to a bigger battery (and alternator) can alleviate the power issues that can potentially arise. 

That’s all I Need to Worry About?

Not quite. The battery has cables that distribute power to other items (alternator, starter, etc.). The gauge of the cables being ran can greatly affect how efficiently the power is delivered to the necessary items. One key item is upgrading the alternator power wire as well. This upgrade can give a constant power supply and while allowing more power to be delivered, also give room for even further upgrades.

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Red vs. Yellow Top Batteries

One very common brand is Optima. They have been around for quite some time and have batteries for all applications. There are different models for common vehicles, such as red and yellow top batteries. They are called red (and yellow) top because the top cover of the battery will have a particular color, which designates the type of battery it is. The red top battery is the entry model. It is designed for common rugged activities and can be mounted in almost any application. They are generally used for hot rods, trucks, street cars, etc. The yellow top is the high-performance battery line. The yellow top is designed for vehicles that have heavy amounts of accessories, such as speakers, amps, subs, etc. They can also be used for heavy equipment (forklifts, tractors, etc.). The majority of the time, red tops will meet and exceed the battery requirements for the application. That being said, yellow tops do have their place in the performance world, just not many users upgrade systems to the point of mandating a yellow top.

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