spark plugs

Choosing The Right Spark Plugs For Your Engine

Daniel McDonald
Daniel McDonald8 min read
Choosing The Right Spark Plugs For Your Engine

Many drivers take the powerful spark plug for granted. It's a basic but vital mechanism that delivers the spark which ignites the gasoline mixture inside your engine.

But there's a lot more to it. To guarantee optimal engine efficiency, your engine requires a spark plug with the proper temperature, gap, and fit.

Once you've determined the fundamentals, you'll need to choose the optimal spark plug among these constraints. This is the aspect we're here to guide you with.

The Function of Spark Plugs

While the primary job behind the spark plugs is to provide the spark to ignite an air/fuel mixture and start the engine, the engine's spark plugs also remove the heat from the combustion chamber.

Spark plugs function like heat exchangers, delivering the combustor's thermal energy to the engine's cooling system.

Spark Plug Selection

At some time in our lives, we've all assumed that the highest burning, most costly spark plug would be the ultimate pick for the engine.

But unfortunately, the engine's characteristics and specifications define the spark plug you use. Running the wrong plug type or temperature can lead to poor performance, shorter plug lifespan, and potential failure.


Whenever it comes to spark plugs, it's tempting to believe that a higher spark is always better because the primary purpose of a plug is always to ignite the fuel at precisely the right moment, resulting in the combustion required to create the maximum power. However, in order to obtain the optimal combustion, the temp of the spark must satisfy the application's requirements.

In high-compression engines, fuel and air within the combustion chamber are prone to pre-detonation. This is because the temperature of the fuel mixture will increase as it compresses. This implies you want to use less heat to burn all the fuel inside the chamber. In this case, a too-hot plug tip might easily trigger pre-detonation.

When low compression, this spark plug must generate higher temperatures to ignite the full fuel and air combination. If not, the unburned gasoline and air will deposit on the injectors and all over the engine. These deposits are especially appreciative of an engine's performance and economy.

Spark Plugs Types

So, what factors influence plug temperatures? Of course, the substance of the electrode is the first and most significant consideration in choosing plugs for an engine.

Copper Plugs

Copper plugs containing a solid copper core and a nickel alloy electrode have existed for over a century. However, nickel has a substantially shorter life than platinum as well as iridium because it is softer. As a result, these plugs are often recommended for old, low-voltage architectures. In addition, some high-performance automobiles require copper due to their high conductivity.

Platinum spark plugs

Platinum plugs are extremely flammable. This reduces the chance of deposits accumulating, making them ideal for low combustion engines. In addition, platinum plugs have a longer lifespan than copper plugs and can easily last 100,000 kilometers.

Platinum plugs utilize a platinum disc bonded toward the end of the central electrode, allowing the plug to last longer, unlike a copper plug, and hold its edge better, resulting in improved conductivity. In addition, platinum spark plugs run hotter, avoiding fouling and deposit formation.

Double Platinum spark plugs

DIS "wasted spark" ignition systems were developed in the early 1990s, implying that one coil charge regulates the discharge of two fuel injectors in the system.

In doing so, both spark plugs attached to that same coil pack spark during the same time - the difference being that one spark on the compression stage and the other on the exhaust valve of its sister cylinder, which is referred to as a "wasted spark."

To confuse matters further, one spark plug connected to each coil has positive polarity, while the other is reverse polarity.

This plug is strong and durable in DIS installations, lasting up to 80-100,000 miles. If your owner's handbook suggests a dual platinum spark plug, don't use single platinum plugs. The plug will work, but it will wear out quickly and perform poorly.

Iridium spark plugs

Iridium plugs, which are also hot plugs, are used on the same motors as platinum plugs. Since iridium is a tougher, more resistant material than platinum, such plugs can last up to 125,000 miles.

Many late-model automobiles are equipped with these technologically superior plugs straight out of the factory, providing excellent acceleration and fuel economy. Iridium plugs emerged in the mid-2000s as coil-on-plug systems became more popular.

Iridium plugs often have the lowest diameter core, improving efficiency by lowering the voltage required to ignite a spark. If your manual calls for iridium spark plugs, the recommended practice is to accept the extra expense of this rarer metal for optimum performance.

Double Iridium Spark Plugs

Double-iridium ignition coils are similar to double-platinum plugs. Double-iridium spark plugs include two discs composed of rare metal to improve performance and longevity.

Such spark plugs provide firepowers for all driving circumstances, such as excessive heat or constant high speeds. Double-iridium spark plugs can last up to four times as long as a standard copper spark plug.

Boost and Fuel

Compression is important in ignition system selection, but so is a boost. Whenever the application is boosted, the same rules apply as they do in high compression engines—copper plugs are recommended.

It's also worth noting that when installing plugs in any car, you'll need to "gap" them. The spark plug gap defines the location of the spark discharge. Proper gaps are essential for the efficiency of a plug, and each manufacturer recommends a specified gap.

Similarly, because different gasoline types have varying cooling capabilities, they influence plug selection. Alcohol, for example, will cool components faster than gasoline.

Although copper plugs are almost always the right approach for high-performance purposes, all of the above considerations would still play a part in spark plug selection.

Distributors and Plug Wires

The right spark plug is critical for sustaining or recovering an engine's performance. However, it is not the only component of the combustion system that requires your attention. A decent pair of plug connections, a distributor, and a coil are also essential.

Because the coil and coil pack are a source of energy, there's no denying the importance of having a good coil to get things working. For example, if you're handling a carbureted engine, the distributor and plug wires are responsible for transmitting power to its destination.

Wire Connectors

Remember that your stock plug wires will likely provide far too much resistance when you increase engine performance.

In other words, the more power you generate, the more crucial a full burn becomes. So if you want as much energy as possible to reach the plugs, use plug cables featuring low internal resistance.

Don't worry; getting good plug wires doesn't have to cost a significant amount of money. SpeedFX is in the business of providing car owners with high-quality components at reasonable costs.

SpeedFX plug connections are universal for V8 motors and have a resistance rating of 500 ohms per foot. Because they are not preassembled, they are suitable for any application because you may trim them to the proper length and provide a clean look underneath the hood.


Your distributor is in charge of determining which plugs will light and when. The location is vital, but the when is what makes an engine operate.

All the components you put at a motor are worthless if the synchronization is just off. You know this because reduced RPM was wonderful after replacing the distributor, but the unit fell slightly as engine rpm increased. So, what's the deal?

Most distributors use a sophisticated system. Some have mechanical advances, some have vacuum advances, and yet others have a balance of both.

In any scenario, the advance is there to compensate for engine speed. When installing a distributor, the manufacturer specification normally requires that ignition occur about 10 degrees before TDC.

You configure it to ensure the spark has enough time to get to the chamber. This allows it to create energy at the optimal time. Consider it similar to placing a lead on a moving object. The spark must be provided sooner as the engine revs up. That is why the distributor requires some advance.

HEI Distributors

Many people choose to install an HEI distributor as they offer a neater look underneath the hood and are nearly maintenance-free.

While you don't require an HEI to achieve results, another big advantage of this configuration is that the time advance may be readily adjusted.

In addition, its counterweights, springs, and bushings are located immediately beneath the rotor, making them significantly easier to modify than in many other configurations.

Consider SpeedFX once again if you're looking for an HEI. As you might assume, these are some of the greatest bang-for-buck ignition components available.

Adjusting the timing curve yields greater performance increases compared to any other ignition adjustment you can apply to an engine. Regardless of whether the timing is near, bringing this one the remainder of the way could make a big difference in your journey.

Key Characteristics

The following are some of the most significant factors to consider while choosing the best spark plugs.


When purchasing spark plugs, you should consider which substance is appropriate. Copper is appropriate for older models with low-voltage distributor-based ignition. Platinum or iridium are ideal for modern engines that lack distributors.

Platinum offers a fantastic blend of price, performance, and longevity. Despite its higher price, iridium provides an even better combination. Finally, always use the plug advised by your vehicle's manufacturer.


The thread and nut size is a useful technique to specify spark plugs. In the United States, common thread or nut dimensions are as follows: 10 mm (nut: 16 mm), 12 mm (nut: 14 mm, 16 mm, or 17.5 mm), 14 mm (nut: 16 mm or 20.63 mm), and 18 mm (nut: 20.63 mm).

Spark Plug Heat Range

A spark plug is labeled "hot" if it is a better heat conductor and "cold" if it can channel more heat from the tip and reduce its temperature.

Manufacturers often identify the thermal band of an ignition system with a numeral, with some manufacturers preferring ascending digits for hotter plugs while others utilize descending numbers for a colder plug.

Gap Design

Spark plugs frequently have a spark gap that may be adjusted with a gapper kit. A single plug can be designed for many engines, each with its own gap.

The distance between car spark plugs is typically 0.6 to 1.8 mm (0.024 and 0.071 inches). Use a gap gauge to test the plug's gap within the specified range.

Intervals of Replacement

Due to the efficiency of precious-metal plugs, factory-recommended spark plug renewal intervals have often been in the 100,000-120,000-mile range in recent years.

However, these spark plugs can continue to work well even after exceeding these intervals. However, when they reach 100,000 miles of service, it is critical to monitor spark plug performance.

This is because spark plugs require greater voltage to fire as the electrodes deteriorate over time. This strain might cause misfires if it remains unnoticed.

An essential thing to remember when getting spark plugs is never to downgrade. For example, suppose a car arrived with quite a fine-wire platinum ignition system. In that case, the new plug must meet the original standards, regardless of whether the engine has 300,000 mileage.

What Type Of Spark Plugs Would I Require?

The wide variety of spark plugs may appear confusing initially; however, the simplest approach to determine the right plugs you require is to consult your owner's handbook. The correct plugs for your car will be specified in the manual.