Best Spark Plugs for Harley Davidson

You should ensure that your Harley is equipped with top-of-the-line spark plugs regardless of whether you’re a long-time Harley fan or just starting out.

A spark plug of premium quality ensures that the air-fuel mixture is fully combusted, delivering a powerful spark in the process. Moreover, it offers a longer lifespan is highly resistant to corrosion and vibration and can bear extreme temperatures.

If you choose spark plugs carelessly, you can experience a variety of problems, including misfires, excessive fuel consumption, and carbon buildup as well as engine damage.

This is because an inappropriate plug may not be able to properly ignite the gasoline-air blend, leading to combustion that is not complete.

Best spark plugs for Harley Davidson – Our Top 5 Picks!

We’ve listed the best spark plugs to help you maximize your bike’s performance, no matter if you’re a commuter or a racer. 

Our top picks feature the latest technology and most reliable brands, check them out and find the perfect product for your Harley.

1. Denso ‎SK20R11 Spark Plug (Editor’s Choice)

Denso SK20R11 is a highly durable and long-lasting product that stands out in the competition with its 360⁰ laser-welding process and 100,000-mile-long life span. These features make it a great value for your money over the long run.

Denso SK20R11 is crafted from sturdy and reliable Iridium that has a high melting point, high wear resistance, and excellent electrical conductivity. 

With its superior temperature and corrosion resistance, it helps to ensure that the engine can ignite and run reliably, no matter the conditions.

We love that it is welded with the utmost precision and reliability through the use of a 360⁰ laser-welding process. 

Using a laser beam, the metal components are heated melting together and creating a strong and secure connection. This process also eliminates any potential weak spots or air leaks ensuring that your machine is operating as efficiently as possible.

Denso SK20R11 is equipped with ribbed ceramic insulators that help to dissipate heat and keep the spark plug running cooler. It ensures reliable operation and prevents premature engine failure, ensuring long-term vehicle performance.

What We Like

  • Smooth out the ride, making it feel like new again.
  • Quick and easy installation, only around 20 minutes.
  • Strong spark even at high RPMs.
  • Improved performance and acceleration.
  • Durable and long-lasting iridium construction.
  • Default gap matches perfectly for some users.

What We Don’t Like

  • Denso SK20R11 pre-gapping may need to be adjusted to achieve optimal performance.

2. ACDelco 41-993 Spark Plug (Best in the Low Budget)

If you are looking for a cost-effective spark plug that can effectively block electromagnetic waves, energy, and radio frequencies then ACDelco 41-993 is your go-to choice. It has highly efficient one-piece suppressor seals that block all the unwanted disturbances from the system to give a high boost to the engine.

ACDelco 41-9937 is safeguarded against RFI (radio frequency interference) with one-piece suppressor seals, crafted from a conductive material that absorbs and disperses electromagnetic energy. 

By blocking the transmission of this energy, the risk of interference with the vehicle’s electronics is greatly reduced.

Moreover, it is manufactured with a unique Iridium fine-wire construction that’s smaller in size, magnifying its spark focus and ignitability. 

With this powerful spark, the air/fuel mixture is ignited more easily, increasing engine performance and fuel efficiency.

ACDelco 41-9937 gets a serious power boost from platinum center electrode tip technology. The platinum alloy tip is more resistant to corrosion and wear than other materials. 

This characteristic makes it a longer-lasting spark plug that can ignite a more powerful air and fuel mixture in the combustion chamber.

What We Like

  • Pre-gapped at 60 thousandths of an inch (1.5mm).
  • Iridium tipped spark plugs that maintain the gap throughout usage.
  • Improves engine performance and smooths idle.
  • Noticeable difference in engine performance.
  • Perfect fit and long-lasting.
  • Instantly took care of misfire and running smoothly since.
  • Lasts up to 90k miles.

What We Don’t Like

  • May not fit properly with certain plug wires, causing arcing issues.
  • Risk of potential damage from overtightening plugs.

3. E3 Spark Plugs (‎E336) for Harley Davidson

E3 Spark Plugs (E336) is an excellent solution for those who have the desire to make the air clean and want to reduce their carbon dioxide and hydrocarbon emissions. This spark plug has been proven to reduce CO emissions by 58%, and hydrocarbon emissions by 42%.

This E3 model is safeguarded from corrosion and oxidation with nickel-plated terminal ends. The spark plug is subject to intense heat and moisture, but the nickel plating ensures the metal resists oxidation that could potentially cause build-up resulting in a misfire or poor engine execution.

Furthermore, this item has revolutionized combustion with its DiamondFIRE ground electrode technology, a patented design that packs more punch than conventional ignition units.

This electrode also produces an intense spark path up to five times longer than traditional spark plugs, optimizing combustion power.

E3 Spark Plugs (‎E336) is outfitted with a copper center core that quickly conducts heat away from the plug. As a result, a stronger and longer-lasting spark is created, while misfires are reduced due to the more stable flame that the copper core provides.

What We Like

  • Improved performance, including better fuel efficiency and increased power.
  • Easy to start, even in colder temperatures.
  • Noticeable differences in engine sound and overall ride quality.
  • Smoother running engine with better acceleration and fuel efficiency.
  • Reduces emissions and carbon buildup.
  • Works well with various Harley Davidson models, including those with fuel injection and carburetors.
  • Suitable for older, oil-burning bikes.
  • Perfect fit for Harley Davidson models.

What We Don’t Like

  • Long-term durability may not be fully established

4. ‎Champion Copper Plus RN12YC Spark Plug

For those of you who want to buy a Spark Plug that comes with international certification, then Champion Copper Plus RN12YC is the one for you. It is built to meet and exceed ISO and SAE standards to make sure that your Harley Davidson runs smoothly.

Champion RN12YC has a copper core that reduces the heat generated during combustion, helping to prevent it from overheating and potentially damaging the engine

It also offers higher oxidation resistance, making sure that the spark can penetrate the chamber faster, lighting up the fuel mixture in no time.

In addition to that, it has been optimized to reduce RFI (radio frequency interference) and EMI (electromagnetic interference) with the help of the SAC-9 semiconductor resistor. 

The unit is inserted between the metal connector and the insulated body of the plug. By absorbing and dissipating spark interference, the plug operates more smoothly and efficiently. 

Champion RN12YC boasts TinTac and ULTRASEAL technologies. TinTac is a special plating that is applied to the spark plug threads, reducing friction and extending the life of the plug. 

ULTRASEAL is a specialized gasket material created to give a superior seal between the plug and the cylinder head. It helps to keep heat in and keep oil and fuel out of the combustion chamber, allowing for optimal drive output.

What We Like

  • Exact fit for 1996 and 1998 Harley Davidson models.
  • Long lifespan, lasting several years before needing replacement.
  • Includes a resistor to remove any radio frequency interference.
  • Not too hot, beneficial for certain engines.
  • Perfect fit for Harley Davidson EVO.
  • Improves engine performance and runs well.

What We Don’t Like

  • Champion Copper Plus RN12YC doesn’t offer any warranty.

5. ‎Quicksilver 97182Q NGK BUHW-2 Spark plug

Quicksilver 97182Q is a suitable spark plug for those living in a hilly area, as its tungsten center electrode has a high melting point, allowing it to bear extreme temperatures. It will also resist engine heat-up when the bike will be pushing itself on a sloppy road.

Quicksilver 97182Q has been outfitted with a tungsten center electrode that is designed to last and function at the highest level. The melting point of this heavy material is so high that it can withstand even the most extreme conditions. It also provides a better spark arc, resulting in improved combustion and more efficient engine performance.

Moreover, it is fortified with a protective coating of trivalent metals that guard against oxidation, corrosion, and wear and tear. This advanced plating process also enhances the electrical conductivity of the plug providing a dependable spark optimum output and reliability.

Quicksilver 97182Q is constructed with highly efficient iridium, providing tremendous durability and hardness. This remarkable material enables spark plugs to withstand the high temperatures and pressures of combustion while also allowing for a more exact spark gap. 

What We Like

  • Reduce plug fouling, improve heat dissipation, and insulate with an alumina silicate ceramic insulator.
  • The ribbed suppressor seal prevents sparks from jumping and minimizes noise and vibration.
  • At only 0.7 ounces, it is incredibly lightweight and convenient to take with you wherever you go.
  • Made from high-quality Iridium that can last much longer and needed to be replaced less frequently.
  • Resolves some issues related to the engine not running
  • Can improve engine performance and efficiency

What We Don’t Like

  • Quicksilver 97182Q is quite fragile and can be easily broken if it takes a hard hit. Therefore, mount it as soon as you receive it to prevent falls or other dangers.
  • May not be compatible with all engine models

Things to Consider When Buying the Best Spark Plugs for Harley Davidson

Harley Davidson riders understand that the ideal spark plug has the potential to dramatically enhance the power of their bike. It can be tricky to decide which spark plug is the best option for your Harley, so take note of the following tips before making a decision.


The choice of material for your spark plug is critical as it affects the service life and performance of the plug. Copper, platinum, and iridium are the three most commonly used materials, each offering its own set of benefits and drawbacks. 

Copper plugs are the most basic and economical option available. They provide excellent conductivity and are designed to provide a long service life. 

While Platinum plugs, while more expensive, are designed to provide longer life than copper ones. They also give superior resistance to corrosion and a more precise spark. 

Lastly,  Iridium plugs are the most expensive option, but they offer improved fuel efficiency, better performance, and less required maintenance. They have the highest melting point of all spark plug materials, making them the most durable option.

Also Read: How To Adjust Idle On Fuel Injected Harley Davidson

Gap Size

When selecting spark plugs for your Harley Davidson, gap size is a critical metric. The gap between the electrodes must be just right to ensure the spark plug can ignite the fuel mixture. 

Too narrow, and the spark won’t be able to jump the gap; too wide and the spark will be too weak, resulting in poor fuel economy and misfires. 

The size of the spark plug gap on a Harley Davidson varies depending on the size and model of the engine. Refer to the owner’s manual to ascertain the recommended gap size for your engine, as it can range from .030 to .080 inches. 

Ground electrodes

The ground electrode serves as the bridge between the center electrode and the engine, providing a smooth and reliable path for the spark to travel. 

Its design and size are critical for delivering just the right spark energy to the engine, otherwise, misfires, rough running, and poor fuel economy may be the result. Make sure your ground electrode is the correct size and shape, and you can enjoy a smooth ride.

When it comes to ground electrodes, you have the choice of two distinct styles: Double-Tipped and Single-Tipped. Double-Tipped features two small tips that extend from the center electrode, granting greater control over spark energy. 

On the other hand, Single-Tipped has one large tip jutting out from the center electrode, granting a more reliable spark with superior consistency in high-performance applications.

Thread Size

When outfitting your Harley Davidson with spark plugs, thread size is an essential factor to consider. Three distinct dimensions, Reach, Diameter, and Pitch, must be chosen correctly to ensure the engine runs optimally. 

The Reach refers to the length of the thread and how far it extends into the cylinder head. The Diameter is the size of the thread and is usually measured in millimeters. It is usually measured in millimeters or threads per inch (TPI) and is the distance between two adjacent threads.

When it comes to Harley Davidson Motorcycles, one of the most common thread sizes is M12x1.25 millimeters. This size indicates that the thread has 12 millimeters of diameter and a thread pitch of 1.25 millimeters.

Additionally, M14x1.25 millimeters, M18x1.25 millimeters, and M18x1.5 millimeters are also common sizes for Harley’s. To make sure you get the right thread size for your ride, take a look at the side of the spark plug or in the vehicle’s owner’s manual.

Heat range

The spark plug heat range is a measure of how quickly the plug dissipates heat from its firing end. The heat range needs to be matched to the particular bike’s RPM, fuel and air mixture, and exhaust system.

For Harley Davidson, a spark plug that packs a bit more heat is usually optimum for the higher RPMs. The result is a quicker ignition of the fuel and air mixture, as well as a cooler engine. A hotter plug will not only provide more power and torque but will also ensure more complete combustion.

A colder spark plug should be used at lower RPMs. It will keep the engine cool for longer and eliminate pre-ignition and pinging, which is especially helpful for bikes with high compression ratios. Ultimately, the colder plug will aid in avoiding any engine damage caused by pre-ignition.


The insulator acts as a protective buffer, shielding the spark plug from the engine’s fiery combustion chamber. It safeguards the metal shell of the plug from any contact with the engine’s metal components and ensures that the spark remains within the spark plug. 

Moreover, the insulator provides a layer of insulation to the ignition plug, guarding it against the intense heat of the combustion chamber, thus preventing it from melting or getting damaged.

There are three main types of insulators used in spark plugs: ceramic,  porcelain, and alumina. Ceramic insulators are made from a porous material that has excellent heat-resistant properties. 

Porcelain is also highly resistant to corrosion, extending the lifespan of the spark plug. Alumina is the choice for higher-performance applications, as its higher melting point helps it better dissipate heat, as well as providing corrosion resistance for extended use.


Over To You!

Wrapping it up, it’s clear that through Harley Davidson’s reliance on spark plugs to keep their engines going, not every spark plug will do the job right. 

Laser Iridium plugs won’t cut it, as they lack the necessary heat range and firing rate that the engine needs. Also using plugs that are too cold or too hot can cause major damage and major repair bills. So make sure your Harley Davidson’s spark plugs are up to the task.

The Denso ‎SK20R11 reigns supreme among the reviewed products, crafted from an ultra-durable Iridium boasting a sky-high melting point and unparalleled wear resistance. With added benefits such as the 360⁰ laser-welding process and ribbed ceramic insulators that help to keep the spark plug running cool, you’ll be hard-pressed to find a better option.

However, if you’re on a tight budget, the ACDelco 41-993 is the perfect pick. There are one-piece suppressor seals, a unique Iridium fine-wire construction, and a platinum center electrode tip, which is far more corrosion-resistant.

About David Riedel

I am David Riedel founder of Bikerwhizz, I'm a technician at Keystone Harley Davidson with more than 10 years of industry experience. I’m here to help you solve motorbike problems, customizations, tweaks, and easy fixes to enjoy your rides more.

Leave a Comment