8/10
Reliability
9/10
Performance
BMW S55 Engine – 3.0L Twin-Turbocharged Inline-6
BMW’s S55 engine is a 3.0L inline-6 twin-turbocharged, direct injection gasoline engine produced from 2013 to the present day (in the M2 CS Racing). The S55 marked a reintroduction of the inline-6-cylinder engine to the BMW M division after the S65 V8-powered E9X M3. While many M-enthusiasts would likely have preferred a naturally aspirated inline-6 under the hood of the M3, the S55 signaled that BMW was committed to forced induction as the way forward for all M-cars to come.
Like most of the other engines that found their way under the hood of a true BMW M vehicle, the 3.0 twin-turbocharged S55 engine borrows heavily from its non-M counterpart, the BMW N55 engine. Like the N55, the S55 is an aluminum 3.0L inline-6 engine equipped with double-VANOS and Valvetronic variable valve timing. The BMW S55 returned to a true-twin turbo arrangement which was popularized on the earlier BMW N54 engine.
Throughout the BMW S55’s build cycle, it was used in a number of BMW M models including the F87 M2, F80 M3, and F82 M4. Depending on the model, power from the S55 ranged from 359 horsepower to 493 horsepower. Since the S55’s release, it has quickly become one of the fan-favorite BMW engines from an aftermarket potential standpoint.
This page is the ultimate resource for everything BMW S55. We provide a general overview and technical information on the engine in addition to problems, performance modifications, FAQs, and various other resources. Whether you own an S55-powered BMW or are looking to purchase one, we have the most comprehensive S55 information on the internet.
S55 Engine Overview
The BMW S55 is a 3.0L twin-turbocharged inline-6 engine that was designed for the explicit purpose of powering BMW’s coupe and sedan M vehicles including the F87 M2, F80 M3, and F82 M4. Prior to the BMW S55, the BMW M3 was powered by the naturally aspirated S65 V8 engine, which was a major departure from the inline-6 engines that powered both the E36 and E46 generation M3s. A massive reason for the switch to a twin-turbocharged inline-6 for the M3 was efficiency. While the S55 only produced 15 more horsepower initially, it provided a 30% increase in torque and a 28% improvement in fuel efficiency over the previous S65 V8.
Over the course of the S55’s build cycle, it has been released in a number of variants producing different levels of power. While the S55’s overall construction is widely the same across the board, the engine’s tune was modified depending on which model it was placed in. For example, standard M3 and M4 models received 425 horsepower variants of the S55 while M3 and M4 Competition models received a 444 horsepower S55 variant.
Unlike many of the other turbocharged inline-6s that came before it, the S55 is known as an exceptionally reliable engine. BMW undoubtedly learned from the N54 and N55 engines and made necessary changes to improve the reliability of the S55. While the S55 does have typical BMW engine issues, like valve cover and oil filter housing gasket leaks, it has very few unique issues outside of crank hub failure at high-horsepower thresholds.
The S55 is one of the most popular BMW performance engines in the aftermarket community. Due to the S55’s high tolerance for power and its true twin-turbo arrangement, it has tremendous aftermarket support and a massive tuning scene.
BMW S55 Engine Guide – Specs, Reliability, & Modifications
BMW N55 vs S55 Engine Differences
The BMW S55 shares approximately 75% of its components and overall design with the N55 engine found in non-M BMW models from 2009 to 2019. However, BMW made some key changes to the S55’s internal components and overall engine architecture to be able to withstand the higher power output and demand. The primary differences between the S55 and earlier N55 engines can be seen in their block design, cooling system design, turbocharger arrangement, and internal components.
One of the most notable performance-affecting differences between the engines is the difference in their crankcase design. The N55 engine uses an open-deck design, like its N54 predecessor, while the S55 utilizes a closed-deck crankcase. The N55’s open-deck block has the advantage of improved cooling properties, as they feature cooling channels surrounding the cylinders. While the S55’s closed-deck block doesn’t provide the same cooling efficiency, it is far more structurally rigid, allowing it to withstand far more strenuous forces.
In part due to the S55’s closed deck block, as well as the engine’s twin-turbo arrangement and higher overall performance ceiling, it needed a far more comprehensive cooling system than the N55. As a result, the S55’s cooling system is split into two circuits. One is an engine cooling circuit and the other is a charge air cooling system. It also includes oil cooling for the engine oil and transmission.
The S55’s use of a true twin-turbo arrangement is a massive difference between the N55 and S55 and plays the most significant role in how the two engines perform differently. The S55 moved away from the single twin-scroll turbocharger used on the N55 in favor of a more traditional twin-parallel Mitsubishi TF035 mono-scroll turbocharger arrangement.
The S55’s internals and auxiliary systems were also improved including a revised crankshaft, pistons, rods, and oiling system.
BMW N54 vs N55 vs B58 vs S55: Performance & Reliability
BMW S55 vs S58
In 2019, the BMW S58 took the reigns as the premier BMW M engine found in a number of vehicles ranging from the F97 X3M to the G80 M3. Like the S55 which was based on the non-M N55 engine, the S58’s overall architecture and construction was based heavily on the celebrated BMW B58 engine.
Overall, the two engines are pretty similar in terms of their overall design. Both engines are closed deck, aluminum, twin-turbo inline-6 engines with double-VANOS, direct injection, and Valvetronic variable valve timing. While the S58 is still considered a 3.0L engine, it does feature a slightly higher displacement of 2,993cc compared to the S55’s 2,979cc. That is due to the S58’s slightly longer stroke of 90mm which benefits top-end power.
One of the most important differences between the two engines is the S58’s lower 9.3:1 compression ratio, which plays a significant role in the S58’s larger power potential and more linear boost characteristics. Due to the S58’s lower compression ratio and larger turbos, it has more turbo lag than the S55 due to its higher boost threshold. However, that also means that there is more performance to be extracted from the S58, as it isn’t as highly strung from the factory and the larger turbos are capable of providing more boost.
Ultimately, the BMW S58 is an engine built with top-end power in mind and outperforms the S55 higher in the rev range. However, the S55 is more peaky and aggressive earlier in the rev range due to its smaller turbos and lower boost threshold. For more information about the two engines, take a look at our dedicated BMW S55 vs S58 article below.
BMW S55 vs S58: Performance, Reliability & Tuning
General BMW S55 Information & Resources
S55 Engine Specs
| Configuration | Inline-6 |
| Displacement | 3.0L (2,979cc) |
| Aspiration | Twin-Turbocharged |
| Fuel System | Direct Injection |
| Engine Block | Aluminum, closed deck |
| Cylinder Head | Aluminum |
| Valvetrain | DOHC, Valvetronic, Dual VANOS |
| Bore x Stroke | 84 mm × 89.6 mm (3.30 in × 3.50 in) |
| Compression Ratio | 11.5:1 |
| Horsepower | 359-493 hp @ 6,000 RPM |
| Torque (lb-ft) | 295-443 lb-ft @ 1850–5500rpm RPM |
| Redline | 7,600 RPM |
Over the course of the S55’s build cycle, the engine was released in six factory trim levels. The primary difference between the S55 variants is the factory tune, which created a wide variety of horsepower outputs depending on the model. All S55 engines are nearly identical in construction regardless of the model, with the exception being the highest-output S55 found in the F82 M4 GTS which featured a water injection system. Here is a list of all of the vehicles that made use of the BMW S55 engine:
275-359 bhp BMW S55
- 2020–present F87 M2 CS Racing
405 bhp BMW S55
- 2019–2021 F87 M2 Competition
425 bhp BMW S55
- 2014–2018 F80 M3
- 2014–2020 F82/F83 M4
444 bhp BMW S55
- 2016–2018 F80 M3 with Competition package
- 2016–2020 F82/F83 M4 with Competition package
- 2020–2021 F87 M2 CS
453 bhp BMW S55
- 2018 F80 M3 CS
- 2017–2020 F82 M4 CS
493 bhp BMW S55 (Water Injected)
- 2015–2016 F82 M4 GTS
- 2017 F82 M4 DTM Champion Edition
We have compiled some of the most commonly cited BMW S55 engine problems. Overall, the BMW S55 is seen as a very reliable engine, even 10 years after it was released. With that being said, there are still some problem areas with the 3.0L turbocharged inline-6. In addition to some unique issues with the S55, including crank hub issues, the S55 shares quite a few common problems with the N55. S55 oil filter housing gasket leaks, oil pan gasket leaks, and chargepipe failures are the most common issues with the S55 and are good to know about if you drive an S55-powered BMW.
Take a look at the dropdown menu below to learn more about these problems or check out the more in-depth problem and maintenance guides featured below.
The 4 Most Common BMW S55 Engine Problems
Crank hub failure is unquestionably the most commonly cited BMW S55 engine problem by a mile. While there is some legitimacy to crank hub failure being a significant issue on the S55, the frequency of the issue has largely been blown out of proportion.
While the root cause of the problem remains a topic of discussion, there is a prevalent belief that S55 crank hub failure is the result of rpms changing rapidly during upshifting and downshifting, causing a nearly immediate change in crank speed to match the input shaft. The inertia caused by this abrupt change in crank speed can loosen the sprocket. Most of the time, this can cause the sprocket to slip a couple of degrees, throwing off cam timing, requiring the hub to be replaced and the engine to be retimed. In some rare cases, crank hub failure can cause internal damage, but that is usually only the case with aftermarket hubs.
That explanation seems to be consistent with the fact that crank hub failure is much more common on S55 engines equipped with DCTs. S55 crank hub failure also tends to happen far more commonly on heavily modified S55 M3s and M4s, with a minuscule number of stock engines actually suffering crank hub problems.
While there are reports of this happening, the overall percentage of S55 owners that have experienced this issue is very low. Most of the coverage of this problem has stemmed from aftermarket communities trying to overreport the problem to sell replacement parts that have proven to be even more damaging than the factory crank hub should it fail.
S55 Spun Crank Hub Symptoms
- Drivetrain malfunction light
- Limp mode
- Rough idle/stuttering
- Engine fault codes
Unfortunately, there aren’t any warning signs of crank hub failure. S55 crank hub failure isn’t something that occurs over time, but rather fails instantaneously and without warning. Once it occurs you will typically see the drivetrain malfunction light and limp mode. Additionally, you’ll notice a rough idle and stuttering due to the timing being thrown off.
As with most modern turbocharged BMW engines, the BMW S55 engine is relatively leaky at high mileage, primarily due to its high operating temperature. The constant heat cycling combined with the S55’s elevated temperature causes the plastic and rubber gaskets to deteriorate and crack over time. BMW’s choice of gasket material also contributes to the issue, which has proven to be overly brittle on multiple other past engines.
Among the main culprits for oil leaks in the S55 engine is the oil filter housing gasket. S55 oil filter housing gaskets tend to begin leaking around the 60,000-80,000 mile mark due to typical engine wear and tear. While the leak itself may not be overly concerning as long as the engine has sufficient oil, it becomes crucial to address the issue promptly, as a leaking S55 oil filter housing gasket could lead to severe consequences in the long run.
Due to the location of the N55’s oil filter housing and the design of the engine itself, a leak from the OFHG can drip onto the drive belt and pulley, causing the belt to slip off of the pulley, potentially causing damage to other surrounding engine components. Additionally, if the S55 OFHG leaks for a long period of time or leaks severely there is a possibility of oil and coolant mixing.
Overall, an S55 oil filter housing gasket leak isn’t a severe issue that will cause drivability issues unless left untreated for a long time. As with all of the other gasket-related issues on this list, none of these are unique to the S55 or BMW engines in general. Gaskets leak and fail over time and were designed to be replaced and serviced.
S55 Leaking Oil Filter Housing Gasket Symptoms
- Oil leak from oil filter housing area
- Oil on belt
- Low oil
The key here is simply inspecting the OFH and belt area every so often to check for signs of oil leaks. Again, be cautious of oil leaks that are dripping onto the belt. If left too long you may consider replacing the belt & pulleys, as well.
Like many of the other issues on this list, valve cover gasket leaks are another issue that the S55 shares with the BMW N54 and BMW N55 engines. In fact, the S55 shares its valve cover design with the N55 engine. It is inevitable that you will encounter a bad valve cover gasket at some point on your S55 engine. Like most of the other main gaskets, the S55’s valve cover gasket is a serviceable item that tends to wear out around the 100,000-mile mark. A failing or leaking S55 valve cover gasket is caused by repeated heat cycling that leads to the rubber gasket cracking and degrading over time.
In addition to the valve cover gasket, it is relatively common for the S55’s plastic valve cover itself to begin to degrade and crack over time as well. That tends to happen a lot less frequently than a faulty gasket, but there have been multiple reports of failing S55 valve covers, especially at high mileage. If you are approaching the 80,000-100,000 service interval and need to have your valve cover gasket replaced, it might be a good idea to just replace the valve cover along with it.
S55 Valve Cover Gasket Leak Symptoms
- Burning oil smell
- Smoke from valve cover area
- Oil on spark plugs
- Low engine oil light
As long as the leak isn’t so severe as to drain the engine of the majority of its oil, you shouldn’t notice any N55 drive-ability issues. However, there will likely be some minor annoyances like a burning oil smell in the cabin or smoke from the valve cover area if the leak is bad enough. Minor leaks may not produce enough smoke to notice. Excessive oil on the spark plugs is typically a dead giveaway that the VC or VCG is leaking.
Like with numerous of the other problems on this list, S55 chargepipe failure isn’t extremely common on stock S55 engines. With that being said, there have been instances of S55 plastic charge pipes developing cracks or experiencing fatigue as they age. Charge pipe failure is not unique to the S55, as the N55 engine also faced similar issues with its plastic charge pipe. The main reason that BMW charge pipes are known to fail is the fact that they are made out of plastic or polymer blend. Over time, the engine’s frequent heat cycling and high operating temperatures can cause the plastic pipes to warp or crack.
Outside of the chargepipe itself failing, the rubber couplers that connect the charge pipes to the valve-cover-mounted heat exchanger have been known to come loose, allowing the charge pipes to detach from the heat exchanger itself. If that happens, power will be significantly reduced and the engine will likely go into limp mode. To address this problem, certain BMW dealers have found a solution by degreasing the coupler and using sandpaper to create a rough mating area on the charge pipe. That prevents the chargepipes from slipping off.
Once again, this is a relatively uncommon issue for S55 engines running stock boost pressure. However, cracked chargepipes are much more common on tuned S55 BMWs. Luckily, the solution for this issue is very straightforward and easy. Simply upgrading to a set of aftermarket aluminum chargepipes will prevent this issue from happening entirely.
BMW S55 Charge Pipe Upgrade Guide – M2, M3, M4 Chargepipe
S55 Problems & Maintenance Guides
The 4 Most Common BMW S55 Engine Problems
We have the most comprehensive resources for S55 performance upgrades. This section includes some of the most popular, cost-effective, and value-focused modifications for the BMW S55 engine. At this point in time, 10 years after the release of the S55 in the F80 M3, the 3.0L BMW inline-6 has one of the largest aftermarket communities of any modern BMW engine. From tuning information to performance parts suggestions, we have you covered as far as BMW S55 modifications are concerned.
Click on each modification to get a brief rundown of the mod, the benefits, and our best product recommendation. Additionally, we have full in-depth guides for each of these modifications that you will find within the sections. Furthermore, a list of general performance and modification-related content can be found below, covering power limits, boost levels, and various other S55-specific topics.
How to Build a 600WHP BMW S55 M3/M4 for $2,000
BMW S55 M3/M4 Performance Intake Guide
Performance intakes are always our first recommended modification for any turbocharged BMW engine, the S55 included, for a few reasons. For starters, they are inexpensive meaning that they are a great entry point to the aftermarket community for most BMW owners. They are also a great backbone modification for the rest of a high-horsepower S55 build, as most other performance modifications can benefit from additional airflow. And finally, upgraded intakes provide some amusing and performance-enhancing benefits on their own.
Upgraded S55 intakes generally help performance in a couple of ways. Upgraded intakes typically draw in cooler air. That isn’t a massive benefit though, as its impact is limited since the air passes through highly heated turbos before being eventually cooled by the heat exchanger. However, upgraded intakes often feature a less restrictive design compared to the factory setup, allowing for optimal airflow.
S55 intakes either use an open-air or closed-air design, with open-air intakes being exposed to the inside of the engine bay and closed-air intakes being encased in an enclosure. Open-air intakes tend to supply the engine with a larger quantity of air, while closed-air S55 intakes tend to provide slightly lower intake air temperatures. Open air intakes are the more popular choice for the S55, as most people are looking for additional airflow over the negligibly different IATs. Open air intakes also provide a more potent intake noise under acceleration, which is a big reason that some people choose to upgrade their intakes to begin with.
While most naturally aspirated engines tend to only see marginal gains from performance intakes, you can expect to see upwards of 10-15 additional horsepower from an upgraded S55 intake alone or around 15-20 additional horsepower with an accompanying tune and bolt-on mods.
S55 Intake Upgrade Benefits
- Approx. 5-10whp and torque when stock
- Faster turbo spool
- Increased air flow and less restriction
- Quicker throttle response
- Sweet “intoxicating” engine sound
Best S55 Performance Intake
BMW S55 BM3 Tuning Guide – Info & Horsepower Gains
BMW MHD Tuning App – N54, N55, S55, B58 & N13 Flash Tunes
A quality tune is truly the backbone of every BMW S55 build. The world of BMW S55 tuning can get a bit dense, simply because there are so many quality tune options to choose from.
Even without additional bolt-on modifications, a simple plug-and-play piggyback tune, like the ones available through the JB4, can provide gains of up to 80 horsepower on pump gas and up to 120 wheel horsepower on E85. Combined with other S55 modifications like an upgraded intake, high-flow/catless downpipes, and fueling upgrades, a tune can turn your S55 into a 600+ horsepower track monster rather easily.
One popular S55 tuning option is a piggyback tune. Unlike a flash tune which augments the factory DME parameters, a piggyback tune simply changes the boost parameters of the engine and allows the factory DME to sort out the rest. Piggyback tunes also piggyback can also alter certain signals and sensors to accomplish other tuning goals. Piggyback tuners, like the JB4, essentially act as advanced boost controllers, leaving the factory DME unchanged. While some people argue that N55 piggyback tuning is inferior, options like the JB4 come with more functionality and for a relatively low price. Many piggyback tuning options also allow for back-end flash tuning as well, which combines the best of both worlds.
The other primary S55 tuning option is a flash tune. An S55 flash tune (like Bootmod3 provides) essentially rewrites the factory DME programming. This allows the tune to gain complete control of engine tuning parameters like boost, fueling, timing, and load. Most people in the BMW community have started to move more toward the flash route as flash tunes generally provide a more customizable approach to tuning, with some advanced features that aren’t possible with piggyback tuning. Bootmod3 is perhaps the most popular BMW S55 tuning solution on the market.
If you are interested in learning more about both S55 flash and piggyback tunes, take a look at our dedicated S55 tuning guides linked above.
BMW S55 Upgraded Downpipes Guide
Upgraded downpipes are one of the most important elements of modifying an S55-powered M2/M3/M4. The downpipe is a part of the exhaust system and sits directly behind the turbocharger. Ultimately, the factory downpipes were built with emissions in mind and sacrificed a bit of performance as a result. The OEM S55 DP’s feature catalytic converters (cats) which hamper exhaust flow from the turbo to the rest of the engine’s exhaust system. Eliminating those restrictions results in reduced back-pressure behind the turbos, allowing them to spool faster and build more boost.
You ultimately have two choices for upgrading your S55’s downpipes. You can opt for high-flow downpipes that swap the OEM cats for high-flow versions allowing for greater airflow, or you can opt for catless downpipes which remove the factory downpipe catalytic converters altogether. There are pros and cons to each option.
In a side-by-side comparison, catless S55 downpipes are less restrictive, leading to improved power, torque, and less spool time. However, catless downpipes do have one drawback. Catless S55 downpipes will almost guarantee a failure on state inspections and emissions testing, meaning that you’d likely have to swap back to the factory downpipes before emissions testing every time. For those who prioritize avoiding potential emissions-related problems, catted downpipes might be a more suitable choice. While high-flow S55 downpipes will unquestionably yield impressive power gains as well, the benefits won’t be as pronounced as with catless downpipes.
S55 Upgraded Downpipe Pros
- 20-25whp (10-15whp w/ catted DP’s)
- Comparable torque gains
- Less turbo lag & lower boost thresholds
- Improved top-end performance
- Exhaust sounds
Best S55 Downpipe
BMW S55 Charge Pipe Upgrade Guide – M2, M3, M4 Chargepipe
Like the N55, the BMW S55 engine uses plastic chargepipes that are known to crack and fail over time, especially if you are pushing more than stock boost. The primary charge pipes prone to failure on the S55 are known as the hot side chargepipes. They are the connection from the turbochargers to the top-mount intercooler. At higher-than-stock boost pressure, they are known to either blow out causing structural damage to the pipes themselves, or pop off of the top-mount connection causing the biggest boost leak possible. One way to resolve that issue is by upgrading to a set of aftermarket aluminum S55 chargepipes.
The factory chargepipes can handle about 22-25psi of boost before we would strongly recommend upgrading them. However, there still are some reasons to upgrade the S55’s factory chargepipes. If you want to run meth injection you will need a chargepipe with a meth bung since the factory one does not have one. In addition to the durability and room for future chargepipe-related mods, aftermarket S55 chargepipes are often far less expensive than the crumby stock one and easy to install, making them a no-brainer modification.
Best S55 Chargepipe
Fueling modifications are a pretty common topic when it comes to high-horsepower BMW S55 builds, as pump gas will only get you so far before you start to run the risk of pre-detonation. Fueling generally enters the conversation somewhere around the 600whp mark, or about the time that you max the stock turbochargers.
Ethanol blends are very popular in the high-horsepower BMW community for good reason. Ethanol mixes combust at a lower threshold which keeps cylinder temps lower, preventing the risk of pre-detonation. They also serve as an octane booster, which means the overall BTU rating for each burn cycle is higher than that of gasoline. That results in better overall engine performance. It is important to note that you’ll need a tune that is optimized to run an ethanol blend in order to reap the benefits and prevent damage.
E30 is a popular ethanol mix for S55 owners that are pushing higher than stock boost pressures that don’t want to do a full fuel system overhaul. E30 is a blend of 30% ethanol and 70% gasoline which introduces some of the benefits of ethanol without being too much of a burden on the stock high-pressure fuel pump.
Since E85 requires about 30% more fuel than traditional gasoline for equal combustion, the stock high-pressure fuel pump and injectors struggle to accommodate the extra fuel requirements. If you are planning on running full E85 on your S55, it is a good idea to upgrade both of those components.
Additional fueling modifications, like running water-methanol injection, is also extremely important to consider at high horsepower and boost levels due to its benefits of reducing engine temperatures, knock suppression, and a bump to power numbers. For more information about S55 water/meth injection, take a look at our article below.
BMW S55 M2, M3, M4 Water Methanol Injection (WMI) Guide
BMW S55 Intercooler & Heat Exchanger Upgrade
An upgraded S55 intercooler & heat exchanger combo is a highly debated modification for the S55, as the factory cooling system is already very good at what it does from the factory. As we already covered, the S55 features a separate charge air cooling circuit from the engine cooling circuit in order to keep charge air temps at their absolute lowest. Additionally, the S55 features an improved air-to-water intercooler design that is much more effective than the previous air-to-air systems on previous turbocharged engines like the N55 and N54.
So, why upgrade your S55’s intercooler and heat exchanger? Well, there are a couple of reasons that people claim to upgrade their OEM IC and HE, but we’ll let you make up your mind as to whether or not it is worth it for you.
If you aren’t pushing the limits of your factory turbos, it is unlikely that an upgraded charge air cooling system is worth it for you. However, some people say that the bar and plate intercooler core used on most aftermarket S55 intercoolers is more durable and has better cooling capacity than the fin and tube core used on the stock intercooler at high horsepower levels. However, there isn’t much evidence to support the fact that they truly make a significant benefit over stock.
For some people, it is a matter of preventing potential issues with the OEM top-mount intercooler which has been known to leak in some circumstances. There are a number of reports of the OEM air-to-water intercooler leaking into the intake manifold and exhaust valves and into the combustion chamber itself, causing serious engine damage. While it is rare, most aftermarket air-to-water S55 intercoolers feature a revised design, preventing that from happening.
Check out our BMW S55 Upgraded Intercooler and Heat Exchanger article for more information on the subject.
BMW S55 M3 & M4 Upgraded Twin Turbo Guide
BMW S55 M3 & M4 Single Turbo Upgrades
If you’ve gotten this far, chances are that you’ve maxed out on S55 performance mods and are ready to take it to the next level. Either that or you are curious to see what options are out there when you do reach that stage. Ultimately, upgrading the turbos/upgrading to a single turbo setup, isn’t for the faint of heart or wallet. Maxing out the stock S55 turbos will put your build somewhere in the 700+ horsepower and 650-700 wheel torque ballpark which is beyond the capabilities of the stock DCT and nearing the limit for the S55’s internals.
Generally speaking, if you are planning on installing a new turbo setup, you’ll want to build the S55’s bottom end if you are looking for any kind of sustained reliability over 750-800 horsepower. While we won’t go too in-depth on the topic here, torque is the real engine killer, as you run the risk of bending the stock rods at around the 700-wheel torque mark. There are a lot of considerations when choosing turbo upgrades so we suggest reading our complete guide above that gives you a bunch of different options for various different power levels, but we’ll cover the basics here.
Ultimately, you have the option of running either an upgraded twin-turbo setup or switching to a single-turbo setup. There are benefits to running both S55 turbo setups. Larger S55 twin-turbo setups will keep factory-like boost characteristics with less turbo lag, more low-mid range torque, and a lower boost threshold. A large S55 single turbo upgrade will have a higher boost threshold, slower spool but more top-end power. S55 single turbo setups actually tend to be safer to run at higher horsepower levels, as the lack of low-end torque limits the risk of pre-detonation from high sustained cylinder pressures.
Additional S55 Performance Guides
BMW S55 M3 & M4 Single Turbo Upgrades
BMW S55 M2, M3, M4 Water Methanol Injection (WMI) Guide
BMW S55 BM3 Tuning Guide – Info & Horsepower Gains
BMW S55 M3 & M4 Upgraded Twin Turbo Guide
We have a comprehensive article that covers performance upgrades, power levels, general maintenance, problems and reliability, and more for the S55. We’ve included a few performance and reliability-related questions below but recommend reading our full BMW S55 engine guide for more extensive questions and details about the BMW S55 engine.
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How much power can the S55 handle?
The S55 can handle around 700wtq on the stock engine block and internals. Horsepower isn’t really the issue here, as low and mid-range torque is what truly does damage to engine internals on highly tuned S55 engines. With the right tune, the S55 engine is capable of withstanding upwards of 800 horsepower on the stock block and internals. The most common place for a BMW S55 engine to fail is its connecting rods, which tend to bend beyond the 700wtq mark.
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How much boost can the stock S55 turbos handle?
The factory S55 turbos are capable of making up to roughly 30psi. In most cases, the factory S55 turbos are good for low-600 horsepower figures before a turbo upgrade is needed. However, for reliability and longevity reasons, we recommend limiting boost to about 25-26psi. Much over 25psi pushes the turbo well outside its efficiency range for minimal performance gains. Even at that boost level, reliability is questionable. Additionally, altitude increases cause the turbo to work harder.
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How reliable is the BMW N55?
The S55 is known for its impressive reliability, even now, 10 years after its initial release. There are very few truly common problems with the S55 engine, with the majority of issues springing up as a result of age or extensive tuning and modifications that the factory engine can’t handle. Most of the S55’s problems revolve around wear-and-tear components like the valve cover gasket and oil filter housing gasket. However, some issues like crank hub failure and charge pipe failure are generally caused by fatigue from high horsepower and torque levels. With proper maintenance and diligence, the S55 engine is one that should last a very long time under the hood of an M2/M3/M4.
In-Depth FAQ Guide
BMW S55 Engine Guide – Specs, Reliability, & Modifications
8020 Media S55 Videos
Other Helpful S55 Videos
Outside Resources
We have dozens of guides on the BMW S55 – check out all of our S55 content below or use the tabs to find our articles on specific modifications, and so on. However, there is also a ton of good content elsewhere around the S55. Check out a few of our favorites here:
All BMW S55 Engine Content
BMW S55 M3 & M4 Upgraded Twin Turbo Guide
BMW S55 Intercooler & Heat Exchanger Upgrade
BMW S55 M3/M4 Performance Intake Guide
BMW S55 Upgraded Downpipes Guide
BMW S55 vs S58: Performance, Reliability & Tuning
How to Build a 600WHP BMW S55 M3/M4 for $2,000
BMW N54 vs N55 vs B58 vs S55: Performance & Reliability
