Best Spark Plugs for Harley Davidson – Reviews

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If you own a Harley Davidson, chances are that you are passionate about your motorcycle. Yet, even diehard riders often mistakenly think that all spark plugs are created equally. Having the proper spark plugs is one of the most important things you can do to make sure your bike runs its best.

5 Top-rated Spark Plugs for Harley Davidson

I can’t count how many times I have heard of owners spending dozens of hours, and often considerable sums of money, trying to diagnose an issue on their bikes only to realize they were using the wrong spark plugs. Even the most premium spark plugs are still a comparatively minor expense overall, and so this is an area where it simply doesn’t make sense to compromise. However, it can still be difficult to know which spark plugs are the correct choice for your Harley Davidson. What are the best spark plugs for Harley Davidson? Here’s what you need to know.

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1. NGK DCPR7EIX – Iridium Spark Plugs for Harley Davidson

NGK Iridium IX DCPR7EIX Spark Plugs for Harley Davidson Twin Cam

NGK is one of the oldest names in spark plugs, and their products are always a safe bet. The DCPR7EIX is an iridium electrode model which contributes to its excellent reputation for reliability and performance. Compared to a standard electrode, the spark-gap performance of an iridium electrode has improved conductivity. This allows for a smaller electrode surface area and a hotter spark and even a weaker ignition system to still provide optimal performance for your bike.

The electrode on a sparkplug is analogous to a garden hose. The smaller the tip, the more forceful the spark will be for a given voltage or amperage. Thus, the smaller electrode of the NGK Iridium IX DCPR7EIX is a great way to guarantee optimal performance for your Harley Davidson.

This Isn’t The Best Option for a Performance Setting

While the NGK Iridium IX DCPR7EIX is unquestionably a great OEM replacement plug for your Harley, it is not the right choice for all applications. Because of the comparatively small electrode area, this plug is designed to produce a hot spark with a smaller flame-surface area. This means that the flame surface will be less likely to propagate in higher performance engines. This can have two impacts.

First, in a high displacement engine, such as one that has been bored or stroked, this plug may have a difficult time producing sufficient spark area to properly ignite the intake charge.

Further, this plug may experience detonation in extremely high-compression racing engines. Thus, if you want a fantastic OEM replacement plug for your mostly stock bike, this is a great option. However, if you are pushing the limits of power, you may want to look elsewhere.

Pros
  • Reliable Power for Stock Engines
  • Hot Flame
Cons
  • Not Suitable for Modified Engines

2. E3.36 – E3 Spark Plugs for Harley Davidson Twin Cam 88

E3 Spark Plugs XL Sportster 883-1200 V-Rod

In contrast to the NGK mentioned above, the E3 Spark Plug E3.36 is a spark plug that can punch well above its weight in a tuned or modified engine. Unlike the iridium plug of the NGK, the E3 uses a yttrium-enhanced alloy for its electrode surface. What does that mean in plain language? This formulation has two main impacts. First, yttrium possesses greater thermal transfer properties, meaning this plug will stay cooler in higher-performance applications.

What’s the Deal with Heat?

In extremely high-compression engines, spark plug temperatures can become high enough to melt the electrode, increase the temperature of the compression charge, or even cause detonation. If you choose the wrong plug for the job, your spark plug can begin to function as a glow plug instead. This will combust fuel at the wrong moment, impacting performance or destroying your engine. In testing, the metallurgy of this plug has been shown to result in temperatures up to 8% cooler.

More Surface Area = More Flame

The other key advantage of the E3 E3.36 plug is the increased surface area. Unlike a traditional plug which has only one electrode surface, the E3 has three arranged in a triangular configuration. Thus, rather than having an offset flame trajectory path, the three electrodes of the E3 spark plug allow for symmetrical combustion propagation leading to a more robust flame front and more even combustion distribution. This increase in the flame surface area makes this an ideal plug for a higher performance application. If you have a higher compression engine, a larger displacement setup, or even a pure race engine in your Harley Davidson, this is a fantastic plug to use.

The Price is Right Too

Perhaps the most impressive aspect of the E3 is the price. Often, high-performance spark plugs can cost multiples of the price of their more pedestrian counterparts. However, this isn’t the case with the E3. Despite the exotic formulation and high-performance credentials, this plug is on-par price-wise with OEM replacements. For any biker who is serious about performance, this is one of the best spark plugs for Harley Davidson.

Pros
  • Flame Propagation
  • Great for Modified Engines
  • Price
Cons
  • May Impact Low-End Power

3. Denso IXU22 – Best Spark Plugs for Harley Davidson Sportster 1200

Denso 5308 Spark Plug for Harley Davidson twin cam 88B

Different applications call for different spark plugs. That is why this overview is not really a review at all, but rather an analysis of the strengths of each plug. While the NGK is an excellent performance plug for a stock application, and the E3 is a go-to plug for modified engines, the Denso 5308 IXU22 is the right choice for a stock bike that lives lower in the rev-range.

Designing a spark plug is often a lesson in compromises. It is impossible to design a plug that performs optimally in all circumstances. Thus, designers are often tasked with designing a plug that is at home in specific rev-ranges. For lower revving applications, this Denso is a fantastic choice.

Contrasting Electrode and Cathode Sizes

As explained above, smaller electrodes tend to result in a hotter spark. This is excellent for high-RPM applications but can result in less power lower in the rev-range. To combat this, Denso designed a plug that has a 0.4mm iridium electrode but a significantly larger cathode. This unique combination leads to a plug that has adequate spark heat for maintaining ignition at high RPM’s, but also provides sufficient surface area for low-RPM grunt. Simply put, this is a spark plug designed for torque.

The Shape Matters

The contrasting sizes are not the only aspect that lends this plug to low-speed cruising. The ground electrode has an electro-etched U-groove that increases the speed of the flame growth during periods of lower intake velocity. Think of it as a ramp for the spark. The other advantage of this design is that the shape of the electrode promotes more efficient cooling of the plug itself. Thus, this plug will continue to provide reliable and detonation-free performance for years.

While this plug is unlikely to win any drag races, that isn’t its intent. Rather, this is a spark plug designed specifically for the best cruising performance at low-RPMs. Thus, if you are looking for a plug to keep your Harley Davidson running its best while cruising the town, this is an excellent choice.

Pros
  • Great Low-End Power
  • Large Flame Surface
Cons
  • Not Good for High-RPM Applications

4. Champion 810 – Spark Plugs for Harley Davidson Road King

CHAMPION 810 spark plug for Twin Cam 88 and 96

Many people think that you only need to replace spark plugs if your engine isn’t running properly, and that spark plugs have little impact on the performance and characteristics of the bike. However, this is a gross oversimplification.

Having the proper spark plug can have a significant impact on the performance reliability of your Harley Davidson. If you are looking for a spark plug that prioritizes reliability over peak performance, the Champion 810 is a plug to consider.

More Area Equals More Reliability

The ignition system of an engine is normally fairly simple. In most cases, an ignition system will consist of a distributor (or its electronic equivalent) that tells each plug when to fire. Then, you have a coil or coil pack that produces the necessary voltage to fire the plug. Finally, you have the plug itself that sparks, igniting the fuel.

Being interconnected, the spark plug will have an impact on all of these components upstream. Although a smaller electrode will produce a hotter flame and result in higher peak performance, it also puts an increased load on the coil. By minimizing the electrode area, the current is increased, and the coil is asked to transfer more current for each ignition pulse. In the short term, this is not normally an issue. However, this effect can weaken or destroy a coil or coil pack over time.

Made wisely

The Champion 810 was designed with this in mind. It uses a particularly large 0.7mm electrode and a 1.0mm grounding surface. Thus, in terms of the electrical contact area, there are few plugs with more. This design reduces the intensity of the spark generated by the plug. While this may slightly impact top-end performance, it also significantly reduces the strain on the ignition system. Thus, for a long-distance or commuter bike, this plug is a superb choice.

Pros
  • Extremely Reliable
  • Large Surface Area Prevents Fowling
Cons
  • Not High-Performance
  • Can be Difficult to Gap

5. Bosch WR8DP+ – Spark Plugs for Harley Davidson Evo

WR8DP+ Bosch Spark Plugs for Harley

While most spark plugs have a specific goal or purpose in mind, not all of them succeed in achieving it. The Bosch 4018 WR8DP+ is designed as an OEM-replacement spark plug for Harley Davidson Evo engines. In keeping with a stock-replacement philosophy, this is not an aggressive plug and is tuned primarily for low-RPM performance. However, the result leaves a fair amount to be desired.

Not All Metal is Equivalent

The first issue with the Bosch WR8DP+ is the metal composition. This plug uses a platinum-yttrium alloy for both the ground point and the electrode. While this composition was cutting edge decades ago, this is an old-fashioned approach from today’s perspective.

Compared to modern plugs, platinum-yttrium plugs tend to demonstrate higher electrical resistance, resulting in a weaker flame and more work for the coil. Further, the heat dissipation qualities of this alloy are comparatively poor. Thus, the spark performance of this plug will be inferior to many modern units, especially over prolonged use.

The Spark Has No Direction

The secondary issue with this plug is the shape and size of the electrode. The modern trend is to use extremely fine electrode points to increase spark force. In contrast, the electrode of this Bosch unit is extremely broad. Worse yet, it is almost completely flat.

Thus, while a modern plug will have a focused spark encouraging an even flame front, the arc-pattern on the Bosch was unpredictable. Because of the relatively featureless electrode, there was no consistency in the propagation of the flame front. This can decrease performance and make an engine harder to tune.

There was a time that this plug would have been acceptable. Yet, with modern advances, this has become one that is best to avoid.

Pros
  • Iconic Looks
Cons
  • Poor Performance
  • Inefficient

6. Orange Cycle Parts – High-Performance Spark Plugs for Harley Davidson

Iridium Performance Spark Plugs for Harley Softail

It would be ultimately pointless to spend too much time analyzing the performance characteristics of this plug because that was never the focus of the design. In function, this is a fairly standard Iridium plug with a 0.5mm single-point electrode. Thus, this is an excellent OEM-replacement plug that will serve well in any relatively stock application. It won’t perform exceptionally well in any context, but it won’t disappoint either.

Looks Matter

The highlight of this plug is the appearance. With its distinctive gold-and-black theme, this is unquestionably an attractive plug. Speaking honestly, many modifications to motorcycles are done more for looks than outright performance. There’s nothing wrong with that. As spark plugs go, this is a beautiful one.

The simple question becomes whether or not the cylinder head design of your bike allows for the plug to be seen, and whether you run a “shorty” insulation boot. If you do, then there’s no reason not to enjoy adding a little extra bling to your block.

The Gold Has Its Price

The only downside to these plugs is the price. For a non-performance-oriented plug, they are unquestionably expensive. This is doubly true when you consider the fact that the gold plating has no real performance advantages. However, they are a distinctive addition to your bike that will provide adequate performance at an ultimately reasonable price. Thus, if gold strikes your fancy, make it so.

Pros
  • Appearance
  • Adequate Performance
Cons
  • Expensive

Tips

Harley Davidson Spark Plug Reviews

As discussed above, the ideal spark plug will depend upon your specific application. However, there are three main variables with spark plugs: metallurgy, electrode size, and electrode number. Let’s take a look at how each affects the performance of your Harley Davidson.

Metallurgy

In recent years, the most significant increases in spark plug technology have derived from the development of new alloys. Yttrium and iridium are the two prominent “exotic” metals that now make their way into plugs. Each has certain advantages.

Yttrium has lower resistance and lowers specific heat. This means that yttrium plugs will produce a hotter spark and will cool faster following combustion. However, yttrium is also more prone to electrical erosion. In contrast, iridium will produce a less powerful spark but will provide for a more resilient and long-lasting spark plug. If performance is the most important factor, choose yttrium alloys. But if reliability is your goal, consider an iridium plug.

Electrode Size

The electrode is the area where the spark itself is generated by the voltage being fed into the plug. Smaller electrodes produce hotter sparks and higher top-end performance. However, smaller electrodes place more wear on your ignition system and erode more quickly. Further, a larger electrode will provide more reliable low-end performance. For a sportbike, go with a smaller electrode of around 0.4mm. For a cruiser? Stick with a chunkier electrode above 0.5mm.

Electrode Number

In many ways, the “multi-electrode” plugs can be thought of as a gimmick. While having multiple spark gaps can improve flame propagation in some contexts, it simply doesn’t make a difference in the vast majority of cases. If you are running an extremely high-displacement or high-compression engine, you may want to consider a multi-electrode plug. Otherwise, save your money and go for the easier-to-gap single models.

FAQ

Who Makes Harley Davidson OEM Spark Plugs?

Harley Davidson OEM Spark Plug

Depending on the specific model, the OEM brand of spark plugs in a Harley Davidson will be made by either NGK or Champion. However, these brands shouldn’t be viewed as your only option given the multitude of reputable aftermarket manufacturers.

What Spark Plugs Do I Need For My Harley Davidson?

Different models of Harley Davidson will require slightly different spark plugs. If you are running a stock engine, the best option is to search for the OEM model of plug for your bike. However, if your engine is modified, you may wish to speak to a qualified tuner for your best option.

How Do You Know When You Need to Change Spark Plugs in Your Harley Davidson?

There are many reasons that spark plugs can need to be changed, including fowling or electrode erosion. If you have noticed that your bike has gotten more difficult to start when cold, idles roughly, or loses power at high RPMs, it may be time to change your plugs.

Harley Davidson Spark Plug Cross Reference

Harley V-Twin Spark Plugs Changing

Not always the OEM spare parts are better than analogs. And it’s not always possible to order the original. In the table below you can find the most frequent and high-quality alternatives for the original spark plugs.

Model \ Brand HD OEM NGK E3 Denso Champion Bosch
XL Sportster 1000 4R5 BPR7HS-10 E3.32 IWF22 RL82YC 0242240561
XL Sportster 900
Panhead/Shovel 1947-1974
XL Sportster 1100
EVO 1340 80″ 5R6A BPR5EIX-11 E3.34 IW16 RN12YC 0242229779
Shovelhead 1975-1981
Shovelhead 1982-1984 5RL BPR5ES-11 RN13LYC
XR 1000 6R7 B7EB W22EPR-U RN7YC 0242245537
Twin Cam 88″ / 96″ 6R12 DCPR7EIX E3.36 IXU22 RA8HC 0242135515
XL Sportster 883/1200
V-Rod 10R12A DCPR8EIX IXU24 RAX94YC none

This spark plug Cross-reference table is for general reference only. Check for correct application and spec/measurements. Any use of this cross reference is done at the installer’s risk.

Final Thoughts

The world of spark plugs has evolved significantly in recent years. Never before has more technology been devoted to an originally simple concept. While different applications can require different types of spark plugs, it is always true that your bike depends on quality spark plugs to run properly. Thus, to get the best performance out of your Harley Davidson, make sure to run the right plugs and replace them as needed. Your bike will thank you.

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