BMW N54 Spark Plugs
2007-2014 N54 Engine
The N54 engine was BMW's first turbo gasoline engine since the 1974 2002 Turbo. Certainly some of the engineers working on the engine weren't even born yet! So a few hiccups and teething problems were to be expected. The N54 has suffered from a few long term issues, with the ignition system being close to the top of everyone's list of annoyances.
Ignition problems are usually misfires - the ignition coil and spark plug are unable to completely burn the air/fuel mixture as expected. Knock sensors, exhaust gas temperature sensors, and oxygen sensors tell the engine computer that something is off. Misfires can be caused by several different things but failed ignition coils or worn spark plugs are the main culprits.
The original recommendation for spark plug replacement was 45,000 miles - way less than the 100,000 mile plugs of previous BMWs. If left in the car for too long the plugs wear to nothing and will no longer fire. This is usually preceded by poor fuel mileage, hard starting, and rough running. There is only one direct replacement OEM N54 spark plug, made by Bosch (part # ZGR6STE2 or BMW #12120037244). NGK does not offer a direct replacement stock plug for this engine. The Bosch plugs use a Nickel-yttrium and copper electrode which works well under a wide variety of temperature conditions and fuel grades. It's exactly what you want for a mass-market OEM plug and it's what we recommend for everyday use on a non modified 135i/335i/535i.
In the tuning world, adding more boost and more fuel calls for changes and upgrades in other areas. Whenever more fuel is burned the temperature inside the combustion chamber rises. The higher temps lead to fuel igniting separate from the spark plug. This is called pre-ignition and is very similar to misfires. We fight this by using a spark plug that does not burn as hot, also known as a "colder" plug. This reduces temps inside the combustion chamber and avoids pre-ignition. There are several colder N54 spark plugs available, depending on your state of tune. There is no "rule" for when to move to a colder plug. Obviously if you have persistent misfire issues that are not from bad plugs or failed ignition coils then it might be time to try a colder plug. For the sake of arguments, we're going to rate these by expected horsepower output but other factors may dictate a colder plug at lower power output.
|-1||up to 420hp||NGK Laser Iridium ILZKBR7B8DG|
This NGK N54 plug is one step colder on the heat range scale. It's also a stronger iridium-tipped plug instead of the stock Nickel-Copper for more consistent performance under high boost. It's good for an N54 with full bolt-on upgrades (FBO): intake, software tune, intercooler and chargepipe, cat-less downpipe, and exhaust but still on stock turbos and running pump gas (no meth injection).
|-2||420+hp||NGK Laser Iridium SILZBR8D8S|
This plug is 2 steps colder on the heat range, which lowers combustion chamber temperatures and reduces misfires and knocking (pre-detonation). This also happens to be the stock OEM plug for the N20 four-cylinder turbo engine. This colder plug should only be used on very highly modified N54 engines, such as with FBO, upgraded turbos, and/or water/meth injection.
2011-2016 N55 Engine
The N55 has not suffered from the same misfire and detonation issues that the N54 did. Part of that is because it takes a lot more effort and time to get to the same boost levels the N54 makes easily. With a FBO N55 output is still only around 380hp and colder plugs have not been a requirement. With the S55 used in the M3/M4 (425hp) BMW did use a plug that was slightly colder on the heat range. This plug was also extended to the N55T0 engine used in the F87 M2 (370hp). So it stands to reason that BMW saw a need to reduce the potential for knocking on the M models. That may be for performance reasons but also to avoid customer complaints and warranty claims. We know that the M4 GTS uses the same Bosch ZMR5TPP330 plugs as the standard M4 so these plugs should be more than adequate at power levels up to 480-500hp (and more than enough for a tuned N55 335i/435i).
|0||up to 380hp||Bosch ZR5TPP33S|
As mentioned above the stock N55 does not make enough boost to require a colder plug. Even with FBO and meth injection, race gas, or E85 blends it struggles to make enough boost to crack 430hp. Colder plugs are not a necessity and the stock plugs should be adequate up to 380hp and then a colder plug may be extra insurance.
|-1||over 380hp||Bosch ZMR5TPP330|
This is the OEM spark plug used in the N55T0 engine in the F87 M2, as well as the S55 engine in the F8X M3/M4. We assume BMW used a colder plug here for the greater boost and higher combustion chamber temps found in the M2/M3/M4 (even the M4 GT4). Therefore this plug should be good up to around 480hp. Research is ongoing to find a plug that is colder and can be used on the M2/M3/M4.
Spark Plug Heat RangesOne note about spark plug heat ranges: the number in the middle of a Bosch or NGK part # is the heat index of the plug (ZGR6STE2). But Bosch and NGK heat ranges are not comparable! Bosch and NGK use completely opposite heat ranges for their plugs! Bosch numbers decrease for colder ranges while NGK digits increase. Don't base any comparisons from that digit unless the brand is the same. If you look at the two examples above the Stage 1 is a 7 and the Stage 2 is an 8. But just because the Bosch is a 6 doesn't mean anything. In the Bosch world, the higher numbers are the hotter plugs!
Are there any downsides to running a plug that is too cold? Yes there are. If you're not at the boost necessary for a colder plug, these will have less ability to ignite the fuel mixture so the engine will run rich. This will cause drivability issues on its own but will also decrease the life of catalytic converters and oxygen sensors. There will be a loss in power as well. These colder plugs also have less expected lifespan as OEM plugs - the colder N54 plugs should be changed every 20,000 miles (half the life of OEM plugs). It's not recommended to automatically jump to the coldest plug available. Try the -1 plugs first and if misfires remain - and all other potential causes are ruled out - then move on to the -2 plugs. Also consider the climate and if the engine has to operate in sub-freezing temperatures. An engine seeing track use in Arizona will have a greater need for colder plugs than one used for daily driving in Connecticut. Colder regions will need to allow more warm up time (or switch back to the hotter plug).
N54, N55 OEM Spark Plugs & Upgrades:
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