N55 spark plugs can be a nuanced topic as far as variety is concerned. While spark plugs are pretty straightforward parts as far as their actual purpose is concerned, choosing the right N55 spark plugs for your application can require a lot of research. This is especially true if your N55-powered BMW is heavily modified.
Beyond simply choosing the right spark plug for your N55, there are other considerations that you also have to take into account. For example, heavily modified N55’s typically require that the spark plug gap be changed in accordance with your horsepower figure. You’ll also have to pay attention to the heat dispersal rating of N55 spark plugs, typically referred to as colder plugs.
In this guide, we’ll answer some of the most common questions about selecting spark plugs for your N55. We’ll discuss N55 spark plug intervals, the instances where colder spark plugs might be needed, and gapping information according to N55 power level. We’ll also give a few N55 spark plug suggestions towards the end.
Spark Plug Heat Ranges
When we refer to a spark plug’s heat range, we are referencing how efficient a particular plug is at dissipating heat. In general, colder spark plugs are better at dissipating heat away from the spark plug tip, in turn lowering the temperature of the spark plug’s tip. A hotter spark plug is better at insulating heat, meaning that the tip retains a higher temperature.
So, what does that mean for an N55 engine? Well, the difference between hot and cold spark plugs really becomes important if you have done any performance modifications to your N55. If you have a boost controller or aftermarket tune that increases your N55’s boost pressure, additional heat is generated in the combustion chamber. While OEM N55 spark plugs have a mild temperature rating, they aren’t equipped to dissipate the additional heat generated by higher boost pressure.
Too much heat can have adverse effects on a spark plug not intended for the job. If your spark plugs aren’t cold enough to cope with the additional heat, they can overheat or cause pre-ignition. If a spark plug is too cold for your given application, it can foul earlier than normal. This is because they are too good at dissipating heat and therefore fail to burn off carbon deposits that build up on the tip.
According to NGK, one of the most premium spark plug manufacturers, claims that it is best to use one heat range colder for every 75-100 hp increase as a general rule of thumb. They also say that it is best to err on the side of too cold of a plug, as premature fouling is better than potential engine damage from too warm of a plug.
While that rule generally stands, there is a limit. For instance, if your N55 is pushing truly crazy horsepower numbers, it might not be necessary to go a step colder for every 100 hp increase. This is especially true for N55s that have been tuned to over 750 horsepower.
BMW 535i, 335i, 135i Spark Plug Intervals
BMW recommends that you change your N55’s spark plugs every 60,000 miles. This figure is pretty much dismissed by the vast majority of the BMW community. As a general consensus, the most commonly quoted life of OEM N55 spark plugs is closer to 30,000 - 50,000 miles. With that being said, there are a ton of factors that go into how long N55 spark plugs can truly last.
For example, if you use your N55-powered BMW as a commuter vehicle and drive primarily on the highway, your spark plugs will likely last closer to BMW’s suggested plug life. However, if you have a modified N55 with increased performance figures, you likely won’t get as much life out of your spark plugs. N55 spark plug life is also dependent on the manufacturer. In general, Bosch/BMW branded plugs tend to last longer than equivalent NGK plugs, especially on tuned engines.
Here are some rough figures that cover N55 spark plug life depending on your level of modifications:
- Stock - 30,000 to 50,000+ miles
- Tune - 15,000 to 30,000 miles (tune-only or tune + minimal bolt-ons)
- FBO - 10,000 to 20,000 miles
- Upgraded turbos: 7,000 to 15,000 miles
The more modifications equipped on your N55, the shorter the lifespan will be on your spark plugs. While a spark plug replacement can be a pretty inexpensive and easy job for those that know their way around a spanner, it is an important consideration to keep in mind if you intend on going all out on your N55.
N55 Spark Plug Gapping
In addition to the heat rating of your N55 spark plugs, you'll also need to consider the spark plug gap as well. It's important to have a good spark plug gap for many reasons. Too large a gap can cause misfire issues while too small a gap can reduce air-fuel burn efficiency. So, what is the right gap for N55 spark plugs? As with most of the other spark plug considerations that we have covered so far, it depends.
What Does Gapping N55 Spark Plugs Actually Do?
In simplest terms, the spark plug gap affects the voltage required to bridge the gap and actually ignite the air-fuel mixture in the cylinder. A larger gap requires more voltage. Increasing gap size can actually lead to a more efficient burn since it increases the spark area. However, high cylinder pressures (compression ratio & boost) can blow out the spark if the gap is too large.
There’s a balance to be found between having a gap wide enough to maximize efficiency and not being too wide as to fail to ignite the air/fuel mixture because of the high pressure within the engine. That middle ground can oftentimes be hard to find, as the changes in spark plug gaps are so small.
Recommended N55 Spark Plug Gaps
Gapping your N55 spark plugs typically only comes into play when some modifications are involved. In most cases, the stock gap for most of the N55 spark plugs on the market is good for applications under 450-500 horsepower.
In general, it is a better idea to start with the stock spark plug gap and adjust accordingly down the line if the performance isn’t to your liking. Spark plug gapping is a very delicate process that requires a bit of finesse and accuracy. Like heat range, spark N55 plug gaping is dependent on your horsepower. Here are some of the most common gaps for different horsepower ranges:
- Stock-450whp: Stock gaps on any Bosch or NGK plugs from above. Rarely a need to adjust
- 425-525whp: 0.024"
- 500-600whp: ~0.022"
- 550-700whp: ~0.020"
- 600-700+whp: ~0.018"
The spark plug gap is also heavily dependent on the types of modifications that you have done to your N55. Aspects like boost pressure, fuel type, and ignition timing all play a part in the best spark plug gap. If you're moving from stock turbos at 400whp to upgraded turbo(s) at 600+whp you'll probably want new plugs and start with a roughly 0.022" or 0.024" gap. If you notice misfires then go to 0.020" then 0.018" if you're still having issues. So on so forth.
Best N55 Spark Plugs
Quite a few N55 spark plug recommendations are informed by spark plug recommendations for the N54 engine that preceded the N55. In some ways that makes sense, in others, it doesn’t as it is generally concluded that the N55 requires one step colder plugs than the N54 due to its higher performance.
In this list, we’ll name some of the most common N55 spark plugs that are tried, tested, and proven. There are a few spark plug manufacturers that have established dominance in the BMW community and are good choices primarily due to their pedigree. With that being said, there are quite a few plugs that will work with the N55 and this list won’t be entirely comprehensive.
It is also important to note that the power figures listed here are not definitive numbers. Some N55 owners opt to use factory spark plugs beyond the 450 horsepower mark and some choose to use colder plugs at stock power. It truly does boil down to personal preference and experience.
1) N55 OEM Bosch ZR5TPP33 Spark Plugs (Stock-400whp)
Bosch ZR5TPP33 plugs are typically the go-to as far as N55s with stock, or slightly higher stock power are concerned. As we stated earlier, N55 spark plugs are generally one step colder than their N54 counterparts. That is the case for the ZR5TPP33. In general, OEM plugs are good for power ranging between 350-400 horsepower. Any more than that and you’ll have to start considering colder plugs.
The true test of whether these plugs are right for your application is running them and seeing if you encounter any misfiring issues. If you do, chances are that you’ll need colder plugs. Stock N55 Bosch plugs are generally the cheapest option available at $95.00 a set.
Purchase Here: BMWSparkplugs.com
2) N55 NGK SILZKBR8D8S Spark Plugs (Stock-500whp)
NGK is another very reputable spark plug manufacturer and a common choice for performance BMWs. The SILZKBR8D8S are one step colder than stock, meaning that they are the better option for modified N55 engines up to 500whp. NGKs feature an iridium-coated construction with a copper-tipped core, which generally helps extend longevity. Even so, with a heavily modified N55, you’ll likely have to replace the colder plugs every 15,000-20,000 miles.
These plugs are best gapped to 0.020” for optimal engine performance. While NGKs are an aftermarket plug, they are also commonly recommended for use in the N20 and N26 engines as well. Overall, NGK SILZKBR8D8S are a great option if the stock N55 Bosch spark plugs just aren’t cutting it anymore.
Purchase Here: BMWSparkplugs.com
3) N55 NGK 6205 LKAR9BI9 Spark Plugs (400-700whp)
The NGK 6205 is our pick for the best two-step colder plug option for the N55. At this temperature range, this plug would only really be the best choice for an N55-powered BMW that is pushing some crazy horsepower numbers. At anything less than 400whp, the life on these plugs would be miserable in comparison to some slightly warmer options.
The 6205 NGK plugs are gapped from the factory to 0.035"/0.036." They also say that the minimum gap that you can effectively run on these plugs is 0.024,” which is important to keep in mind. It is also the only plug on this list that features a threaded stud at the top, meaning that you’ll have to find screw-on solid tops for them in order for them to work with an N55.
Purchase Here: NGK.com
BMW N55 Spark Plug Guide Summary
Spark plugs are a crucial part as far as N55 performance is concerned. Bad spark plugs, or spark plugs not suited for your vehicle’s setup, can have a negative effect on engine performance and can potentially do damage if the plugs are too hot for your application.
There are a few considerations that you have to keep in mind as far as N55 spark plugs are concerned. The temperature range of your chosen plugs is important, as you’ll need plugs that disperse heat better if you are running performance modifications. One or two-step colder spark plugs are best suited for N55s with high-performance output. The spark plug gap also matters quite a bit. In general, high-performance N55s with significant upgrades need a smaller spark plug gap than in stock form. Heavily modified N55s will also need spark plug changes much more frequently than N55s in stock form.
There are quite a few N55 spark plug options on the market that will work just fine. However, there are a few manufacturers that have a very strong relationship in the BMW community that are well trusted. These include Bosch, NGK, and Champion. The plugs listed above are all solid options for your N55, but keep your performance requirements in mind.