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Spark Plugs

Article by: GTRaptor


Sparkplugs play one of the most important roles in any combustion engine: ignite the fuel
Manufacturers match their sparkplugs to the specific engine and ignition needs, and for that reason, the recommended OEM part is most of the time the best choice for your engine.

Motorcraft plugs are of great quality and we at AFM will definately recommend them for your Pony as the #1 Choice.
When possible we will post the information concerning other OEM replacement brands such as , NGK, Accel, Bosch, Champion, Autolite and others.


Spark plugs come in all shapes, sizes, and materials, but also heat ranges which must be matched to your engine needs.
Here are some guides to help you select the best plug for your application.

A petrol engine needs three things in order to function properly: air, fuel and a spark. The spark plug ignites the air/fuel mixture, producing the combustion that powers the engine. In January 2002, Robert Bosch celebrated a hundred years since it was awarded the patent for the first spark plug.

Designed to be combined with a high-tension magneto ignition system, the spark plug solved what Carl Benz had described as the most ‘fundamental obstacle’ to early motoring. Together with improvements in production technology, the spark plug laid the foundations for the rapid increase in vehicle production over the decades that followed.

Early version spark plugs, used in low-speed, low-compression petrol engines, had a life of just 600 miles as compared to the modern copper-nickel spark plug, which lasts up to 18,000 miles. The spark plug is a key engine system component, playing a major role in fuel economy, clean, efficient combustion and the reliable operation of engines and catalytic converters. A typical spark plug will spark up to 100 times per second or more than 20 million sparks over its useful life.

Although the useful life of a spark plug has been extended, its basic function has not significantly changed since the early 1900s. What has changed, however, are the requirements for emissions and service life.

Prior to 1974 in the US, for example, the main concerns which influenced the plug’s design were that it fitted properly, operated at the correct, self-cleaning temperature and that it minimised demand on the ignition reserve. Nickel-chromium was the material most commonly used. In 1974, the US government imposed fuel mandates and regulations to reduce emissions. These required the use of unleaded fuel and led to the introduction of smaller engines and new engine designs, all of which prompted changes in spark plug design. From this point, two factors drove spark plug design: first, since unleaded fuel has a higher burn-off temperature, the plug’s heat range needed to be broadened, enabling it to reach the self-cleaning temperature at lower loads and to avoid overheating at higher loads. Secondly, the spark plug needed to perform consistently in order to prevent damaging the catalytic converter.

As a result, new materials offering improved corrosion and erosion resistance and providing greater capacity to transfer heat were integrated into the design. One such material was copper, used for the plug’s core and surrounded by nickel-chromium. Introduced in the early 1980s, this design provides excellent heat transfer, a wider heat range and improved anti-fouling. By the end of the 1980s, most spark plug makers had switched to using copper core, which remains the standard today.

Yet copper isn’t the only material that has been combined with nickel chromium to improve performance. In 1960, Bosch recognised the value that platinum added to automotive spark plugs, providing improved corrosion and erosion resistance and a longer performance life than found with the standard copper core plug. Bosch then introduced the first platinum tipped plug. The company later advanced the use of platinum in spark plugs when it converted the platinum tipped plug design into a spark plug featuring a centre electrode that is 99.9% pure platinum. This plug, the Bosch Platinum, was introduced to the North American market in 1985. It features a centre electrode made entirely of platinum that is sintered, or heat fused, into a ceramic insulator.

Platinum can withstand temperatures of up to 1,600 degrees Fahrenheit and so less metal is lost during firing. It is also more resistant to corrosion and pitting than traditional copper and nickel alloy electrodes. In early 1984, Bosch became the first manufacturer to agressively market a platinum-tipped plug. Driven by federal legislation, the fitment of platinum-electrode spark plugs has risen dramatically since the mid-1980s. Industry estimates suggest that around 95% of cars sold in North America come equipped with platinum-tipped spark plugs. The majority (90%+) of GM, Ford and Chrysler vehicles have platinum or double platinum spark plugs. The Japanese vehicle makers based in North America are at similar fitment levels. Overall, about one-quarter of the North American car parc is currently equipped with such precious metal plugs.

Three Steps To Selecting a High Performance Plug
When using this guide, understand that high performance spark plugs are usually of a much colder heat range than standard automotive or street plugs. Colder heat ranges must be used in engines with increased cylinder pressures and temps and higher brake-specific power output. Racing engines are stressed to extreme limits and require a specially constructed spark plug to operate in that environment. The first area to investigate will be the type of shell needed. In order to gather this information you must know the thread diameter, length and seat type required by your cylinder head. Do not use a removed spark plug as a guide for determining proper shell dimensions. Failure to get accurate information in this area can result in decreased performance and damaged engines. The second step is to select a gap style that will maximize your performance based on your operating environment. The third step is to select the heat range that corresponds with the required shell and gap style. We recommend that you start your selection of heat range on the cold side of the available plugs and work your way up to a hotter design by reading the plug. Once a plug has been selected, it should be installed and run during practice with the motor "cut clean" to allow proper reading of the plugs. Remember, make only one change at a time. Do not make spark plug changes along with injection/carburetion or timing changes as this can result in misleading or inaccurate conclusions.

Step 1: One-Shell Design and Selection
Physical inspection of the cylinder head is required to determine the thread diameter, thread length or reach, and the type of seat design used by the cylinder head. The thread diameter can be 10, 12 or 14mm. The length of the threaded portion of the spark plug, as measured from the end of the threaded area to the seat, varies from .375" to .750". Either a gasket type or a tapered seat type of seat design is used by the cylinder head. Failure to determine the right type of seat can result in inconsistent heat range and potential engine damage (refer to the chart below).

Step 2: Selecting Electrode & Gap Designs
Generally speaking, the more the spark gap is exposed to the air/fuel mixture, the easier it is to initiate combustion. This translates into improved throttle response and more efficiency.

Step 3: Heat Range Selection
The term "heat range" refers to the relative temperature of the core nose of a spark plug. The words "hot" or "cold," when used in referencing spark plugs, are often a source of confusion and misunderstanding, since normally a hot spark plug is used in a cold engine (low horsepower) and a cold plug in a hot engine (high horsepower). The terms actually refer to the heat rating or thermal characteristics of the plug; more specifically, the plug's ability to dissipate heat from its firing end into the engine cooling system. A cold plug transfers heat rapidly away from its firing end into the cooling system and is used to avoid core nose heat saturation where combustion chamber or cylinder head temperatures are relatively high. A hot spark plug has a much slower rate of heat transfer and is used to avoid fouling where combustion chamber or cylinder head temperatures are relatively low. The primary means of adjusting heat range are by varying the length of the core nose and the alloy material used in the electrodes. Hot plugs have a relatively long insulator nose with a long heat transfer path. Cold plugs have a much shorter insulator nose and thus, transfer heat more rapidly (see illustration; hot to cold - left to right). The heat range of a plug does not affect the power output of an engine. Rather, it allows the plug to function as designed for the duration of the racing event. In other words, once the correct heat range is found that prevents fouling and does not contribute to the pre-ignition or detonation, a change to a hotter or colder plug will not have a positive effect on engine performance.


MOTORCRAFT PLUGS (and OEM replacements when noted)


Motorcraft spark plug for 1982-1995 Mustang 5.0L with Edelbrock heads.


Motorcraft spark plug for 1994-1995 Mustang 5.0L.


Motorcraft spark plug for 1982-1983 Mustang 5.0L, 1984-1985 HO 4V, 1987-1993 5.0L.


Motorcraft spark plug for 1979 Mustang with build date before 2/1/79, 1980-81, 1984-85 with CFI.


Motorcraft spark plug for 1979 Mustang with build date after 2/1/79.


Motorcraft spark plug for 1993-1995 Cobra.


Motorcraft spark plug for 1999-2000 Cobra 4.6L.


Motorcraft platinum spark plug for 1996-1998 Cobra 4.6L.


Motorcraft platinum spark plug for 1999-2000 Mustang GT 4.6L.


Motorcraft platinum spark plug for 1996-1998 Mustang GT 4.6L.


Motorcraft spark plug for 5.0L with GT-40 heads.


Motorcraft spark plug for 1986 Mustang with EFI.

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