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We'll break this down into the following sections:
- General N55 Information
- N55 Standard Maintenance
- Common N55 Engine Problems
- N55 Tuning & Modding
*We will add to this post over time. Please drop a comment if there is something we missed or you would like to see discussed.
General N55 FAQ's
What is the BMW N55?
The BMW N55 is a 3.0L inline 6 turbocharged, direct injected gasoline engine produced from 2009-2019. BMW's N55 engine succeeded the N54 engine, but moved to a single turbo design as opposed to the twin turbo N54. The N55 also followed the N54's footsteps winning 3 straight Ward's 10 Best Engines awards. It is most notably found in 2011-2015 BMW 335i models.
What BMW's use the N55 Engine?
The BMW N55 is found in the following BMW models:
- 2011-2013 135i
- 2012-2013 135is
- 2012-2016 M135i
- 2013-2016 M235i
- 2016-2018 M2
- 2011-2015 335i
- 2013-2016 435i
- 2010-2017 535i
- 2011-2018 640i
- 2012-2015 740i/Li
- 2012-2015 X1 35i
- 2010-2017 X3 35i
- 2014-2016 X4 35i
- 2014-2018 X5 35i
- 2014-2019 X6 35i
How Much Horsepower does the BMW N55 have?
Initial N55 models came out with 300 horsepower and torque, as with the BMW N54. Like the N54, BMW's N55 engine was underrated from the factory. Dynos show stock N55's making upwards of 280whp and 280-290wtq. This translates to about 330hp and 330-340tq.
Later model N55's, such as the N55B30T0, found in the BMW M2 make 365 horsepower. Additional N55 variants fall in between the 300-365hp range.
Does the N55 Have Forged Internals?
No. The N55 uses cast internals. Although not as strong as forged, the N55's internals are still quite durable.
How Many Miles Will the N55 Last?
The N55 will likely last as long as you are willing to continue repairs and standard maintenance. Most N55 internal components should easily hold up well past 200,000 miles. It's typically the components around the engine that may become costly over time.
What is the N55 Compression Ratio?
10.2 to 1. The N54 and N55 both share the 10.2 compression ratio.
Is the N55 Twin Turbo?
No, the N55 is a single turbo engine. BMW dubbed it "TwinPower Turbo", which causes confusion and even lawsuits. You can read more about N55 TwinPower Turbo here.
How Many Valves Does the N55 Have?
The N55 has 24 valves. It is an inline-6 double overhead cam (DOHC) engine. As such, each cylinder features 2 intake and 2 exhaust valves. 4 valves per cylinder times 6 cylinders equals 24 valves.
How Fast is the BMW N55?
From the factory, most N55's are speed limited to 155mph. Removal of the speed limiter allows for top speeds closer to 165-175mph, depending upon the specific model. Modded BMW N55's may eclipse 180mph.
BMW N55 Standard Maintenance FAQ's
What are the Common N55 Standard Maintenance Items?
We are only focusing on engine maintenance specifically (ignoring brakes, batteries, etc). The most common N55 standard maintenance items are:
- Fluids (oil & coolant)
- Spark plugs and ignition coils
- Walnut Blasting / Intake Valve Cleaning
Additionally, we are ignoring air filters since we recommend upgrading to an aftermarket performance intake. Typically, aftermarket options are cleanable and do not require frequent replacement.
How Much Oil Does the N55 Hold? What is the N55 Oil Capacity?
N55 oil capacity is 6.9 quarts (6.5 liters) of oil. This is the exact same as the N54 engine.
What Oil Weights are Approved on the N55?
0W-30, 5W-30, 0W-40, and 5W-30 are all approved oil weights for the N55. Again, this is the same as the N54 engine. The weight you choose does not matter too much. However, we recommend sticking with one weight for the life of the engine. We've always run 5W-30. This oil weight works perfectly well in cold Colorado winters and extremely hot Houston summers.
What is the Best Oil for the N55?
LiquiMoly 5W-30 is our oil of choice. Excellent German oil that we recommend to others. Many great engine oils exist for the N55. We could spend all evening debating the different oils and finding arguments as to why one is better or worse than the other. Ensure you're picking an LL-01 approved oil and you'll be good to go.
How Often to Change N55 Oil? Recommended N55 Oil Change Interval
N55 oil changes should be done every 5,000-8,000 miles. Or once a year - whichever comes first. Specific oil change intervals depend upon your driving style and habits. If you're an "aggressive" driver and like to use the power frequently around the city then you're likely best sticking towards the lower end. Tracked N55's may even consider changing oil as often as 3,000 miles. If most of your driving is highway cruising then you can get away with 8,000 mile oil changes.
If you go past these recommendations, your N55 isn't going to suddenly blow up. However, frequent oil changes will help ensure a longer future.
How Much Coolant Does the N55 Hold? What is the N55 Coolant Capacity?
N55 coolant capacity is 10.5 quarts (10 liters) when completely drained. When doing a coolant flush there are roughly 1-1.5 liters that do not drain. It's typically not worth it to worry about that so expect to fill up on 8.5-9 liters.
What is the Best Coolant/Water Mix on the N55?
A 50/50 mix is common for the N55. Water is actually better for cooling purposes but higher water concentrations worsen the freezing point. Coolant also helps prevent corrosion. A 60% water and 40% coolant mix is likely best for those living in warmer climates. Some even go up to 75%+ water for track duty. However, beware of using too much water in cooler climates.
Is N55 Coolant Really Lifetime?
Not really. We don't agree with the lifetime coolant designation, and recommend flushing the N55 coolant at least every 80,000-100,000 miles. However, a lot of N55's will experience coolant leaks or cooling system issues beforehand. Go ahead and knock out the coolant flush at that time, if any coolant is even left.
How Often to Change N55 Spark Plugs?
The N55 is hungry for spark plugs, especially when modded, and they should be changed fairly often. We recommend the following N55 spark plug change intervals:
Go on the higher or lower end depending upon your driving style. Those who like to frequently call upon the N55's power should sway towards the lower end. Modest, highway driven N55 spark plugs may even last a bit longer than the above intervals. Nonetheless, spark plugs are a standard maintenance item subject to wear and tear. They rarely fail quickly, but rather become less effective with age and mileage.
Don't overlook the spark plugs. They are essential to your N55's performance. Old, worn spark plugs may cause several problems such as misfires, rough idle, and cold start issues.
What N55 Spark Plugs are Best?
OEM N55 spark plugs are an excellent option for N55's under 400whp. However, we ultimately recommend running NGK 97506 1-step colder spark plugs for modded N55's running 350+whp.
Either option is a solid choice on stock turbo N55's. However, the 1-step colder spark plugs from NGK are oft regarded as the best spark plugs for modded, turbo BMW engines. Tons of N54, N55, S55, N63, N20, and S63 owners alike run these NGK 97506 plugs with great success.
Why Run Colder Spark Plugs on Modded N55?
Colder spark plugs are more effective in transferring heat away from the spark plug tips. Modded N55's running increased boost subject the spark plug tips to additional heat. This may cause misfires or engine knocks. 1-step colder spark plugs save the day. These plugs assist in transferring heat from the N55 spark plug tips and reduce the risk of misfires or knocks.
How Often to Change N55 Ignition Coils?
Like spark plugs, ignition coils are a standard wear and tear item. Also like plugs, the N55 loves to burn through ignition coils pretty fast. We recommend the following N55 ignition coil intervals:
Once again, ignition coil intervals should be decided by mods and driving style. Upgraded turbo N55's may burn through coils faster, while modestly driven coils may last a bit longer. Most will likely fall somewhere between the two extremes.
What is N55 Walnut Blasting?
Direct injected engines, such as the BMW N55, cause issues with carbon build-up on the intake valves. Oil blow-by is naturally produced by the N55 and travels through the intake tract. Port injected engines have the advantage of fuel that is sprayed into the intake ports and wipes off any oil deposits. However, fuel is sprayed directly into the cylinder on the N55.
As such, there is no fuel to wipe away the carbon (oil) deposits on the valves. Over time, they become gunked up and reduce airflow into the engine. This is where walnut blasting comes into play. It's a relatively labor intensive job and is normally $400-600 at an indy shop. Walnut blasting involves using walnut media shells to "blast" the carbon deposits off intake valves.
How Often to Walnut Blast N55?
N55 walnut blasting should be done roughly every 80,000 miles. Some even do it as frequently as 40,000-50,000 miles. Additionally, some go past 100,000 miles without ever walnut blasting.
How to Prevent N55 Carbon Build-Up on Intake Valves?
The only truly effective way to eliminate N55 carbon build-up is adding a second fuel rail utilizing port injection. Port injected engines also experience some carbon build-up, but it is very minimal. At least, minimal enough to the point walnut blasting likely isn't worth it.
Some claim methanol injection prevents carbon deposits on the N55. It may help slow down carbon build up a little bit. However, methanol injection is unlikely to completely prevent carbon build-up. There simply isn't enough meth flowing to have a significant impact.
Oil catch cans are another topic of debate for carbon prevention. N55 oil catch cans may also help a little, as with meth injection. But again, it's unlikely to have a significant impact.
How Expensive is N55 Standard Maintenance?
Well, first off, BMW standard maintenance is usually more expensive than your average car. Turbo engines are also more demanding on standard maintenance. Quality LL-01 oil can be pricey. The N55 loves to burn through spark plugs and ignition coils. Point being, standard maintenance is not extremely cheap. Although, it is typically very manageable, especially for the DIY crowd. Expect the following standard maintenance costs:
- Oil & Filter Changes - ~$60-70
- Spark Plugs - $95-125
- Ignition Coils - $219-249
- Walnut Blasting - $400-600
Add in some extra costs if you plan to have the work done at a shop. Additionally, expect extra costs like brakes, transmission fluid, etc. This maintenance is generally more expensive on N55 35i models that often feature larger, more aggressive brakes.
BMW N55 Common Engine Problems FAQ's
Is the N55 reliable?
Yes and no. Overall, don't expect the N55 to be as reliable as a Toyota or Honda, for example. However, it is definitely a reliability improvement over the BMW N54 engine. That may not say too much given how poor a reputation the N54 has garnered.
Some reliability comes down to how well the N55 has been maintained. Some simply comes down to the luck of the draw. We wrote about the 5 most common BMW N55 problems. The below list includes some additional common problems without as much analysis or detail.
What are the Most Common BMW N55 Engine Problems?
- N55 Oil Leaks:
- Valve Cover and Valve Cover Gasket (VC/VCG)
- Typically around 100,000 miles. May pop up sooner
- Oil Filter Housing and Oil Filter Housing Gasket
- Around 100,000 miles. Not uncommon to leak earlier
- Oil Pan Gasket
- North of 100,000 miles is common. Leaks may develop sooner but this is typically the last gasket to go. Absolutely ensure you replace this gasket if the subframe is dropped for any reason.
- Valve Cover and Valve Cover Gasket (VC/VCG)
- N55 Cooling System Problems:
- Water Pump
- Expect the N55 water pump to fail prior to 100,000 miles. It's relatively uncommon for them to go much past that mark. You may even consider doing this as preventative maintenance if you make it to 100k on the original pump.
- Expansion Tank
- The coolant expansion tank is prone to cracking with age. This will usually outlast the water pump but it may be a good opportunity to knock this out at the same time.
- Coolant Hoses
- Like the expansion tank, N55 coolant hoses are prone to cracking and developing leaks over time. Expect a coolant hose to give out at some point, especially north of 100,000 miles
- Water Pump
- N55 Belt & Tensioner
- Though an improvement over the N54 design, this is still a good item to knock out past 100,000 miles. It will likely last a bit longer, but never a bad idea to replace preventatively. Especially pay attention to the N55's belt if your oil filter housing is or was leaking. The leak may drip oil onto the belt, which is not a good thing.
- ****N55 Charge Pipe****
- All of the stars are there to help you, hopefully. Upgrade the N55 charge pipe immediately. It is an easy DIY and relatively cheap. The crappy plastic OEM N55 charge pipe is prone to cracking, even on stock boost. Save yourself from being stranded on the side of the road and knock out this upgrade.
- N55 High Pressure Fuel Pump (HPFP)
- Probably not really worth mentioning. However, it is notable since early model N55's did have some HPFP issues. Most of the older, faulty pumps were likely replaced by now. However, some old ones may still be around. The newer re-designed fuel pumps are pretty solid, but still suffer occasional failures.
- N55 VANOS Solenoids
- N55 vanos solenoid issues usually come up around 120,000 miles. Some people try cleaning the solenoids once the begin going bad. However, it's a short term solution if it even helps at all. Don't worry about replacing these as preventative maintenance. They won't leave you stranded but we recommend replacing rather than cleaning when the time comes.
- N55 O2 Sensors
- We consider this more of a standard wear and tear item. O2 sensors typically require replacement around 120,000 miles. Please note - the O2 sensors rely on each other for calibration. The post-cat sensor still matters even if you're running a catless downpipe.
- Vacuum Lines
- Vacuum lines cause the dreaded under-boost codes, such as 30FF. Not as common a problem as with the N54. However, something to look into if you're experiencing boost under target issues.
The above is not a completely exhaustive list of potential problems. Early model N55's are beginning to near a decade old. Almost any problems are fair game on older, high mileage examples. Again, the N55 is generally more reliable than the preceding N54 engine. It's also a turbocharger, performance engine so don't expect flawless reliability and cheap repairs.
How Expensive is the BMW N55?
It's tough to say exactly how expensive an N55 will be to own. For the DIY crowd, the N55 should be a relatively inexpensive engine. However, it may mean spending the occasional weekends in the garage beating you head against a wall. Oil leaks are common and gaskets are inexpensive repairs. Though, they can be tedious, exhausting repairs. For those going to a repair shop for every issue, repair bills can add up quickly. A simple $30 gasket oil leak may be a $1,000 job at an independent repair shop.
Age also plays a big part in overall reliability and cost. As you likely noticed, there are quite a few items to tackle around the 100,000-120,000 mile ballpark. Look for an N55 that has a fair chunk of this maintenance already done. Or, stick with a newer, lower mileage N55.
Why is my N55 Idling Rough?
Rough idle is a common problem not only on the N55, but many BMW engines. Worry not, though. There are quite a few problems that may cause rough idle. However, often times they are easy, inexpensive issues. If your N55 is idling rough, consider the following:
- Spark plugs
- Ignition coils
- VANOS solenoids
- Fuel injectors
These are just a few of the possible causes. The top 3 are by far the most common causes of N55 rough idle. HPFP and/or injector repairs are much pricier, but are not as common.
BMW N55 Tuning & Modding FAQ's
What is the Best N55 Tune?
The N55 market is flooded with aftermarket tuning options. We advise spending some time researching and choosing the best option for your personal goals, needs, and budget. However, we recommend starting with one of the following N55 tunes:
The JB4 is a piggyback tuning option and is our favorite BMW tunes on the market. Some people knock the piggyback, but we believe they are excellent starting tunes. Piggyback tunes essentially "trick" the ECU (also referred to as DME) and function as advanced boost controllers. The JB4 sets the boost target and relies on the factory DME tune to make the necessary adjustments. As such, they are limited by the parameters of the stock tune. However, here is the awesome part. The JB4 can be stacked with flash tunes, known as back-end flashes. More on this in the next question below.
MHD and bm3 are excellent flash tune options. You really can't go wrong with either. However, E chassis N55 models do not have the bootmod3 option. Additionally, the bm3 is more focused on custom tuning options. It's a bit pricey up-front and custom tunes add extra costs. MHD offers a better selection of off-the-shelf (OTS) maps.
Ultimate Recommendation: JB4 + MHD Back-End Flash
Is the JB4 a Good Tune for N55?
Somewhat a duplicate of the above, but we'll expand. We love the JB4. Burger Tunings JB4 is loaded with awesome features, constant updates/improvements, and great customer support. It also allows for on the fly map changes. Switch from a modest, daily driver tune to kill mode in seconds. That's just a small portion of what the JB4 offers. It's a great starter tune, but has its limits as a standalone tuning option.
However, couple the JB4 with a back-end flash for the ultimate N55 tuning solution. The JB4 retains its advanced safety controls, awesome features, and precise boost control. Meanwhile, the back-end flash re-writes the factory DME to allow for greater tuning capabilities. JB4's are stacked with custom back-end flashes on almost every record holding N54 and N55. As such, it's not only a great starter tune but the JB4 is also run on some of the baddest N5x's in the world.
How Much Horsepower can a Stock Turbo N55 Make?
Finally, we'll touch on the difference between EWG and PWG N55's. 2014+ N55's are EWG (electronic waste-gate) and have a bit more tuning potential on stock turbos. Maximum stock turbo N55 horsepower is as follows:
- PWG - 400whp
- EWG - 450whp
It's important to note - these are optimistic numbers just about maxing the stock turbo. Horsepower depends on a lot of external factors such as dyno, temperature, altitude, etc. The above numbers are right in the ballpark of the world record on stock turbo N55's. With FBO, E85, meth, aggressive tuning, etc most should expect to see power numbers about 20-30whp lower than referenced above. Though, some of you may have a power happy N55 in perfect conditions that rivals the record holders.
How Much Torque can a Stock Turbo N55 Make?
Like above, EWG cars are going to have a bit more potential. Stock turbo N55 max torque is as follows:
- PWG - 500wtq
- EWG - 550wtq
Again, like the above. Optimistic numbers just about maxing the stock N55 turbo. Most should expect a bit less even when pushing their N55 stock turbo to the limit.
How Much E85 can the N55 handle?
The N55 is compatible for roughly 30-40% E85 on the stock fueling system. E85 requires additional fuel flow so ensure your tune is able to support the mixture you are looking to run. You will need an upgraded LPFP to run higher mixtures. Additionally, an upgraded HPFP is likely required to run 100% E85.
Is E85 Safe to Use in the N55?
Yes. As long as your tune supports the E85 mixture it is totally safe to use. One note - E85 is more corrosive than gasoline so beware about leaving too much E85 sitting in the system for extended periods.
Otherwise, E85 has countless benefits. It burns cooler than gasoline. It also requires more fuel be injected into the cylinder which reduces the chance of engine knocking. All of this means more power. Of course, additional fuel flow required also means worse fuel economy.
How do you Data-Log on the N55?
We wrote an in-depth post about data-logging with a JB4 on the N54. The N55 has slightly different parameters, but the aforementioned post will apply to the N55 for the most part.
What are the N55 Fueling Limitations?
The biggest N55 fueling limitation is the stock low pressure fuel pump (LPFP). Stock LPFP's cap out around 30-40% E85 mixtures. An upgraded LPFP on a stock turbo should get you into the ballpark of 60% E85. Higher E85 mixtures likely have minimal benefits on stock turbo N55's.
However, if you want to go further, expect the stock HPFP to cap before you are able to run 100% E85. Keep an eye on AFR's and fuel pump pressure if you plan to push things to the limit on the stock HPFP.
In order to push past 500-550whp on heavy E85 mixes, the N55 will require the addition of a second fuel rail utilizing port injection. This can be expensive so isn't recommended unless you're running a large turbo and truly pushing the limits of the platform.
What does FBO N55 Mean? What does FBO Stand for?
FBO N55 stands for full bolt-on N55. Typically, FBO refers to a tune, performance intake, catless downpipe, and upgraded intercooler. Some include a full exhaust as part of being FBO. However, exhaust doesn't add much power relative to the cost so we ignore that as being a standard N55 FBO part. Some also include upgraded fuel pumps and inlets as a part of FBO. However, the standard use of FBO refers to the 4 basic N55 bolt-ons initially listed.
What is the Max Boost on N55 Stock Turbo?
About 19-21psi is a good "safe" limit for stock turbo N55's. However, some have run upwards of 25-26psi on stock turbos. Expect EWG N55's to make a bit of extra boost and power. We wrote a quick post about N55 stock turbo max boost here.
What is the Best N55 Catless Downpipe?
We always recommend the VRSF catless downpipe. They make excellent, quality products with competitive prices. It's hard to go wrong with VRSF.
How Loud is Catless Downpiped N55?
A catless downpiped N55 is not too loud. Expect a slightly noisier start up and a deeper, aggressive note during heavy acceleration. The great part is, the catless downpipe is barely noticeable while cruising around town or on the highway. Best of both worlds, in our opinion. More aggressive sounds when you want them without being overly intrusive for daily driving.
A catless downpipe with a performance or catless exhaust may be too loud for some. Stick with just the downpipe if you don't want too much noise.
How Much Horsepower does a N55 Catless Downpipe Add?
Expected hp gains from an N55 catless downpipe are in the ballpark of 10-20whp. Exact gains depend upon tuning and other bolt-ons. A tune and downpipe only N55 will likely fall on the lower end of the range.
How Much Horsepower does an N55 Performance Intake Add?
N55 hp gains with a performance intake range from roughly 5-15whp. A performance intake really only adds power if the stock airbox is limiting or restricting the air flow required. The stock airbox is likely enough to support a tune only and may add very minimal horsepower. However, N55's pushed towards the limit on the stock turbo may see gains in excess of 10whp from a performance intake.
What are the Limits on Stock Internal N55 Engines?
We all know about the reputation the N54 earned with its ability to handle massive power and boost on un-opened engines. Unfortunately, don't expect the N55 to have quite the same durability. That's not to say the N55 is weak.
The N55 should be happy to handle 500-600whp without serious issue. Its cast crank and rods are a limiting factor compared to the N54's forged components. However, the N55 internals remain strong. With proper tuning and monitoring you can likely push past 600whp without issue, but it's pushing the limit.
Engine strength will never be as simple as, "oh yeah the N55 will hold up forever at 610whp, but will blow up immediately at 630whp". It's really a case by case basis. What we do know is this: proper tuning, monitoring (data logging), and supporting mods go a long way in ensuring longevity when pushing towards the limits.