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What Are The Best Spark Plugs For A Ford Mustang?

Written By: Josh Honeycutt

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To perform at its peak, your Mustang needs to have spark plugs that are in good condition and up to the task. Make sure you select a set that is going to last and can handle the power your Mustang is putting out.

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Choosing the right spark plug for you Ford Mustang 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, these are a few things you'll need to consider.

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Facts About Mustang Spark Plugs

  • Factory plugs are used for their durability and emissions qualities
  • Proper heat range is important to remember while choosing a spark 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 which causes the electrodes to last longer and created a consistent spark

One of the most often overlooked items on the Mustang is the spark plug. Most Mustang owners don’t give their spark plug selection a second thought, but this can end up being a costly mistake. Ford rolled the stock 4.6 engines out with Motorcraft platinum tip spark plugs. These plugs are gapped from Ford’s factory at .055 inches. In recent years, many after market companies have researched and developed better spark plugs. These plugs allow for a more complete and efficient burn.

Mustang Motorcraft Spark Plug

Are the Mustang’s 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.

Stock Set of Mustang Spark Plugs

What are Spark Plug Heat Ranges?

The heat range is the temperature at the tip of the spark plug electrode in a running engine. 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.

The Importance of the 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.

Colder Set of NGK Mustang Spark Plugs

Spark Plug Gapping Explained

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.

Different Spark Plug Material

The primary change in spark plug material in recent years has been in the electrode of the plug. In the past, the electrodes were made of nickel or copper. These materials eroded quickly with in town driving and were less than desirable at the track. Modern aftermarket companies use far more durable materials for the electrode. These materials include iridium, platinum, silver, and even gold. The primary advantage being they last longer and produce a more consistent spark kernel. This results in better fuel economy and better throttle response.

Close Up of a Mustang Spark Plug Tip

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 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's 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
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