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The N55B30 engine is one in a long line of BMW inline six-cylinder engines. It takes over from the N54, a wildly popular engine known for its potential for big horsepower. Like its predecessor, the N55 is a turbocharged 3.0L inline-6 cylinder engine utilizing direct fuel injection. It was available in just about every chassis BMW used during its life, including the F01 7-series, F16 X6, and the F87 M2. 

These engines span back to 1933 with the introduction of BMW’s first automotive inline-6, the M78. The M102, BMW’s first turbocharged inline-6, appeared in 1980 and evolved into the M106 before being discontinued in 1986. All of their inline-6 engines then remained naturally aspirated until the N54 in 2006. Turbocharging was a relatively new venture for BMW, and the N54 showed that as it was plagued with plenty of teething issues throughout its life. Following that was the N55, an updated and evolved version of the N54, designed to be more reliable and capable in all situations. 

BMW N55 Information & Technical Specifications

Taking over from the N54 was no small feat. By the time BMW ended its use, the N54 had amassed tons of aftermarket support and was the poster child for European tuners. Though very stout, the N54, was plagued with issues large and small. BMW saw those issues, made a few significant changes, and created the N55 as a replacement.

 

As updates go, BMW kept the same basic layout between the engines. They’re both turbocharged 3.0L inline-6s with dual-overhead-camshafts, and direct fuel injection, though that’s where most of the similarities end. Instead of a twin-turbo layout, the N55 uses a single twin-scroll turbocharger. While not as good for aftermarket tuning, the single twin-scroll turbocharger produces more power over a broader range than the N54’s setup. It also sheds weight and complexity from the engine bay.

BMW N55 Engine Guide N55 Dynograph

The most significant evolution in the N55 is the introduction of BMW’s Valvetronic system. The N55 uses the third generation of the variable valve lift system in conjunction with the VANOS variable valve timing system. Depending on the DME’s request, the variable lift system uses a complex group of arms, solenoids, and gears to open the valve between 0.18mm and 9.9mm at will. That eliminates the need for a throttle body as the throttle pedal directly controls the amount of valve lift. In short, the Valvetronic system means better fuel and power efficiency across the entire RPM range.

The last big update was a switch of fuel injectors. The N54 uses Piezo-style fuel injectors, very complicated but advanced fuel injectors that let BMW be very accurate with their injection in several different circumstances. However, because the Piezos are so precise and complicated, they’re costly to produce and are known to fail regularly. The N55 uses a more conventional-style solenoid-fired injector. They are much cheaper to produce and replace while being significantly more reliable. There are additional updates BMW delivered during the middle of the N55’s use. Let’s get into the different specifications of N55 to highlight them.


N55B30M0

The M0-spec engine was the first N55 variant to leave Munich. Like all N55s, it features an open deck but uses a cast crankshaft and pistons with forged connecting rods. There are two variations of these engines though they both share the same designation. The early examples, only produced for a few months, use a high-pressure fuel pump identical to the N54 driven off the front timing cover. This pump has an internal fault where an o-ring breaks and causes a pressure loss inside the pump. Unfortunately for owners, replacement is the only fix, and the pump is quite expensive. The early engines also use a pneumatic (mechanical) wastegate. They rely on boost pressure to open the wastegate and are reliable but not very advanced.

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BMW N55 Engine Guide N55 x-ray

The M0-spec engines received their updates for the 2014 model year. To rid them of the fuel pump issue, BMW changed styles. The new pump uses a tappet-style finger to produce high pressures, though it’s still driven off the vacuum pump. While more reliable than the old style, it can still develop leaks. The updated M0 also uses an electronically controlled wastegate. Its increased speed and boost control allowed BMW to fit a slightly larger turbocharger. These advancements help the updated engine produce more power under the curve, though peak numbers remain the same. They also make it easier to extract more power through tuning.

However, be careful when extracting more power. Tuners have found that the cast crankshaft will break when pushed beyond a certain point. BMW must have known this as they changed the N55s for the “performance” models. These also use single oil pickup in the oil pan, so you’ll need to be careful to prevent oil starvation issues if you track your M0-spec engine.

Available in

2009–2017 F10/F11/F07 535i

2010-2013 E90/E91/E92/E93 335i

2010-2013 E82/E88 135i

2010–2017 F25 X3 xDrive35i

2011-2013 E70 X5 xDrive 35i

2011–2015 F30/F31 335i

2011–2014 E71 X6 xDrive 35i

2012–2015 E84 X1 xDrive35i

2013–2016 F32/F33/F36 435i

2014–2018 F15 X5 xDrive 35i

2014–2019 F16 X6 xDrive35i

2014–2016 F26 X4 xDrive 35i

 

Engine Type: Inline 6

Displacement: 3.0L (2979cc)

Horsepower: 302 hp @ 5800-6400 RPM

Torque: 295 lb/ft @ 1200-5000 RPM

Compression Ratio: 10.2:1

Max RPM: 7000

Induction: Turbocharged

Cooling: Water-cooled

Injection: Direct Injection

Valvetrain: Dual Overhead Camshafts

Valves: 24 Valve

Bore x Stroke:  84mm x 89.6mm (3.30in. x 3.53in.)

Timing Chain: Single Chain Configuration

Oiling System: Wet Sump

Engine Oil Spec: BMW LongLife-01 FE

Engine Oil Capacity: 6.5L

Required Octane: Premium Unleaded (91+)

Digital Motor Electronics: Bosch MEVD17.2

 

N55B30O0

The O0-spec N55 is a slightly tougher version of the M0, utilizing a forged crankshaft that it shares with the T0. Additional differences from the M0 include a larger intercooler and radiator. BMW expected owners to beat on these engines a little harder thanks to their availability in M-performance models. All O0-spec engines use the updated electronic wastegate and larger turbocharger. Thanks to these additions and a different ECU calibration, the O0-spec makes about 20 more horsepower and nearly 40 lb-ft of torque over the best M0.

 BMW N55 Engine Guide Turbocharger setup

If you’re looking for considerable power potential, this is where you should start. The forged crank eliminates the cracking issues the cast unit in the M0 has. At the same time, the larger intercooler and radiator are a better starting point for increased power as their larger area of effect increases the N55’s ability to stay cooler for longer under increased power levels.

Available in:

  • M235i
  • M135i (Non-US)

 

Engine Type: Inline 6

Displacement: 3.0L (2979cc)

Horsepower: 322 hp @ 5800-6250 RPM

Torque: 332 lb/ft @ 1300-5000 RPM

Compression Ratio: 10.2:1

Max RPM: 7000

Induction: Turbocharged

Cooling: Water-cooled

Injection: Direct Injection

Valvetrain: Dual Overhead Camshafts

Valves: 24 Valve

Bore x Stroke:  84mm x 89.6mm (3.30in. x 3.53in.)

Timing Chain: Single Chain Configuration

Oiling System: Wet Sump

Engine Oil Spec: BMW LongLife-01 FE

Engine Oil Capacity: 6.5L

Required Octane: Premium Unleaded (91+)

Digital Motor Electronics: Bosch MSD81



N55B30T0 

The T0-spec N55 is the top of the range, the mack-daddy, and the last one produced. Thanks to various updates, it produces the most power out of any factory stock N55, depending on the trim. BMW learned a ton from the S55 engine and stuck those advancements into the T0-spec N55 fitted to the M2. For starters, the T0 uses the rod bearings and pistons from the S55; however, the top piston ring is unique to the M2 to work with the different cylinder linings.

BMW N55 Engine Guide M2 Engine bay

The T0 also uses the S55’s oil pan specifically so the N55 won’t starve itself of oil on the race track. A large baffle sits in the upper part of the pan to influence the return of oil to the bottom and restrict its movement under hard braking and cornering. Additionally, a scavenge pump sits inside the pan. It’s there to pull the oil out of the turbocharger and front section of the oil pan under extreme G-forces to maintain proper engine oiling. A smaller additional radiator and an oil-to-air cooler are also present on the T0-spec engines, helping them run cooler for longer. Lastly, the T0-spec uses the spark plugs and ignition harness from the S55. The spark plug is one step colder than the standard N55 plug.

All those advancements, along with bespoke ECU calibrations, allow the T0-spec to produce the most power of any N55. Additionally, the T0 has access to an overboost function. For five seconds, the ECU will raise the boost pressure by .1 Bar, or 1.5 PSI, to raise the maximum torque figure to 369 lb-ft. Controlling the boost on the T0-spec N55 is the blow-off valve from the four-cylinder N20 engine.

Available in

  • 2016-2018 BMW F87 M2 (365 HP)
  • 2015-2018 BMW F26 X4 M40i (355 HP)

 

Engine Type: Inline 6

Displacement: 3.0L (2979cc)

Horsepower: 365 hp @ 6500 RPM

Torque: 343 lb/ft @ 1400-5560 RPM

Compression Ratio: 10.2:1

Max RPM: 7000

Induction: Turbocharged

Cooling: Water-cooled

Injection: Direct Injection

Valvetrain: Dual Overhead Camshafts

Valves: 24 Valve

Bore x Stroke:  84mm x 89.6mm (3.30in. x 3.53in.)

Timing Chain: Single Chain Configuration

Oiling System: Wet Sump

Engine Oil Spec: BMW LongLife-01 FE

Engine Oil Capacity: 6.5L

Required Octane: Premium Unleaded (91+)

Digital Motor Electronics: Bosch MEVD17.2

 

BMW N55 Common Problems

The N55 features several much-needed improvements over the issue-plagued N54. Most upgrades fixed the previous engine’s chronic issues, making the N55 far more reliable. However, the N55 isn’t without some issues of its own. Even though they’re less severe than those of the N54, they still need to be taken care of promptly and correctly.

 

Oil Leaks

Oil leaks are about as common on BMW engines as their logo is on their vehicles. For whatever reason, they seem to plague every engine in a very similar fashion, no matter the era. Regardless, here are the spots you’ll need to look out for.

  • Valve Cover - The valve cover on the N55 acts as a valve cover and is the main component in the PCV system. Its plastic construction helps reduce weight and complexity in manufacturing but leads to issues during use. The plastic becomes brittle as the cover is repeatedly heat cycled, making it significantly more prone to cracking. Sometimes, they'll warp and allow oil out from the seal. The seal can also dry up and allow oil to pass by. You’ll notice the wetness around the valve cover when it leaks oil. It’ll leak down onto the exhaust manifold, too, if the leak is persistent.

    However, an oil leak isn’t the only thing that’ll require a replacement. The valve cover is part of the engine’s vacuum reservoir for things like the power-assisted brakes while the engine produces boost. A cracked valve cover means that vacuum pressure will escape, leading to rough running, among other issues. The PCV can also fail inside the valve cover. A failed PCV requires a valve cover replacement as they are one piece.
  • Oil Pan Gasket - The oil pan gasket used to seal the oil pan to the bottom of the engine block is made from rubber and steel. Like the valve cover, constant heat cycling will eventually cause the rubber to separate from the steel and allow oil to escape. A freshly leaking seal will accumulate oil seepage around the unsealed area. If it becomes severe enough, engine oil will drip down the pan and onto the ground. 

  • Oil Filter Housing - The oil filter housing sits next to the valve cover at the front of the engine. The rubber seals that sit between the housing and the engine dry and shrink after consistent exposure to heat. The oil that passes by the seal is under high pressure and constantly leaks while the engine runs.

    The longer you wait to fix this issue, the more things can go wrong. Oil will eventually leak down onto the serpentine belt, causing it to slip off its pulley. The crank pulley will then grind up the rubber belt and force it through the front main seal and into the engine. Those rubber shavings can clog oil passages in the engine, starving components of oil. Special tools are required for a crank seal replacement.

 

High-Pressure Fuel Pump

BMW N55 Engine Guide Fuel Pump Location

The N55 utilizes a direct fuel injection design, meaning fuel is shot directly into the combustion chamber. That system needs two fuel pumps, a low-pressure and a high-pressure. Depending on the year, the N55 will have one of two high-pressure pumps. Know which one yours has so you can address any issues accordingly. 

  • Early Design - At the beginning of the N55’s production, they were fitted with the N54 style HPFP. These pumps sit below the intake manifold towards the front of the engine and are driven off of the back of the vacuum pump. This early style pump is known for a consistent failure of an o-ring inside the pump. The failed o-ring results in a loss of fuel pressure, and the only solution is an expensive replacement. 

 

  • Late Design - Starting with the 2014 model year, the N55s were fitted with a high-pressure pump similar to the type used on the B48 and N20/26. They use a roller-tipped lifter that rides the back of the vacuum pump instead of the rotary design of the old style. Though the new-style pumps are more reliable than their predecessors, they occasionally fail. 

 

Valvetronic Oil Squirter

The Valvetronic system uses a motor and worm gear to activate the variable lift on the intake camshaft. Inside the cylinder head is a dainty-looking oil squirter pointed at the worm gear to lubricate the connection between the gear and Valvetronic shaft. This squirter can get clogged with carbon or sludge, reducing oil flow and causing excess wear on the shaft and gear. Remove and clean anytime you have access to it. Also, change your oil every 5K miles instead of the 10K that BMW specifies to reduce the number of bits circulating through the oil. 

 

Crankshaft Bolt

The main crankshaft bolt is tasked with keeping the timing sprocket jammed against the crankshaft’s nose. Instead of keying the timing sprocket into the crankshaft, BMW decided to rely on the clamping force of the bolt alone to keep them rotating together. Over time, the bolt can loosen. If it loosens enough, the engine will be out of time, valves will hit pistons, and you’re in for a new engine. Vargas Turbo Technologies offers a solution to this potential problem with their “capture” kit, which we do recommend for big-power builds. 

 

Engine Mounts

The stock engine mounts are liquid-filled rubber. Very soft but great at eliminating unwanted vibrations through the chassis. Even in modified applications, they help keep the engine smooth and controlled in the car. However, the stud captured in the rubber portion of the mount is known to rip out, almost always from age, though violent shocks can also break them. Thankfully, they’re cheap to buy and relatively simple to replace.

 

Belt Drive System

The belt drive system makes it into this section because it is often overlooked. The pulleys and belt tensioner that make up the drive belt system are all wear items, meaning they are designed to be replaced from the get-go. However, second-hand owners often leave them out of their maintenance, and they end up causing issues.

The tensioner is mechanical, using a thick spring to provide the tension to the belt. As the engine is used, the spring weakens, losing its tension. You’ll notice that the roller on the tensioner will start to wobble when it loses its effectiveness. The tensioner roller and the other belt rollers all use sealed bearings to keep them spinning. In the same timeframe as the tensioner, these bearings will wear out and start to make a low rumbling noise. If left for long enough, the bearings will seize and can cause the belt to snap. 

 

Water Pump

 

The N55 uses an electric water pump designed to last 65-75,000 miles. The ECU activates the pump via a CanBus signal, which a control module in the pump then interprets. Typically, the control module fails inside the pump rendering it useless. The only solution is a new water pump and a thermostat with it, too. However, faults in the CanBus system can also stop the pump from working. Ensure the pump has failed through proper diagnosis before replacing anything. 

 

Charge Pipe Cracking

As N55-equipped vehicles age, so do the plastics in the engine bay. Constant exposure to heat-cycling causes modern plastics to weaken to the point of disintegration during any involved removal process. The N55's charge pipe is no exception, as constant contact with the turbocharger involves quite a bit of heat. Removing the charge pipe requires a different process between the EXX-chassis and the FXX-chassis. 

BMW N55 Engine Guide Cracked charge pipe

While you're in there, you might want to install an upgraded performance charge pipe from one of the many aftermarket companies making parts for them. Along with some other ", while you're in there" modifications, a performance-based piece should be stronger and perform better. 

BMW N55 Engine Guide Cracked charge pipe

 

Mickey Mouse Flange

The charge pipe is the only plastic component known for breaking. The engine's coolant flange responsible for the coolant intake is another one of those spots. This plastic piece has hot engine coolant constantly running through it. As the engine cools and heats, so does that flange, weakening the plastic. Eventually, they'll crack and likely leave you stranded on the side of the road. At worst, you can install a replacement factory piece and risk it happening again, albeit not for quite a while. At best, you can pick up one of the many aftermarket flanges made from metal to prevent a sudden loss of coolant forever. The choice is yours.

 

BMW N55 Recommended Maintenance

Without the scheduled maintenance, you can guarantee that your N55 will suffer from some serious issues. Engines need to be taken care of in order for them to maintain their health and efficiency. Follow along with the recommendations below and with BMW’s scheduled maintenance intervals to ensure that your N55 lasts well over 100,000 miles.

 

Oil System Priming

If you have to remember only one thing from this guide, make it this section. The N55 has a few issues with keeping its oil inside itself, as addressed above. But what you can’t see is the necessity for you to reprime the oil system after any major repair involving the oiling system is made; that goes for oil pan gaskets, oil filter housing gaskets, any sort of valve train or timing work, etc. BMW sent out a Technical Service Bulletin to all dealerships requiring them to reprime the oil system after those types of repairs. 

According to BMW, their engines were having internal failures from lack of oiling after major repairs due to air pockets in the oiling system. While this TSB refers to all of BMW’s engines, it was caused by N55’s wiping out their bearings after these services. Priming the system involves turning the engine over to generate oil pressure without starting it. The easiest way to do this is to unplug the electrical connections to the fuel injectors and use the starter to turn the engine over. You’ll spin the oil pump, generating oil pressure, without injecting any fuel in for the engine to burn. Prime it for a good ten seconds or so before reconnecting the injectors.

 

Carbon Cleaning

There are several benefits to direct fuel injection, from power to efficiency and everywhere in between. However, it isn’t without its negatives. In port-injected cars, the standard form of fuel injection for the last 50 years, the fuel is sprayed into the engine through the intake runners. The fuel mixes with the air and is pulled past the intake valve and into the engine. The fuel rushing past the valve cleaned it of any oil residue that was present.

BMW N55 Engine Guide Dirty intake valves

Direct-injected engines spray the fuel right into the combustion chamber, allowing the oil to collect on the backs of the intake valve. Over time, that oil collects carbon deposits that build up on the back of the intake valve. This build-up will eventually restrict flow and kill power and fuel economy. The N55 is a bit of an exception as the Valvetronic system significantly reduces the amount of build-up and the amount of time it takes to build up, although it still does occur. 

BMW N55 Engine Guide Clean Intake valves

What you’ll need to do is clean those intake valves through walnut blasting. The blasting machine shoots little fragments of walnut shells at the carbon deposits, knocking them off of the valve and intake runner. Then a vacuum sucks out the walnut shell and carbon bits from the intake, revealing a clean intake valve and runner. While not the easiest, you can complete this cleaning yourself in your driveway or garage; just make sure that you have the right tools first. We recommend checking the intake runners around the 60,000-mile mark for carbon build-up. More than that, you’re almost certainly due for a cleaning. 

 

Oil Change

The BMW recommended service interval for the engine’s oil is every 10,000 miles. Modern synthetic oil is significantly more durable than the stuff automakers used twenty years ago, allowing them to extend those service intervals safely. However, just because the oil can last that long doesn’t mean it should be used for that long. Bits of carbon, oil sludge, pieces of gaskets, and metal shavings all regularly find their way into the oil system. The longer that oil circulates, the more bits get sent around the engine, possibly clogging it. We recommend cutting the service interval in half instead, changing your oil every 5,000. 

 

Engine Air Filter

The engine’s air filter is the only piece preventing foreign contaminants from being consumed by the engine. If anything did get through, it’d likely hit and damage the turbocharger’s compressor. BMW recommends an air filter change starting at 15,000 miles and then every third oil change after that. Really though, the air filter should be changed on a conditional basis, meaning, check the filter every oil change and replace it when it’s very dirty. Different cars drive in different environments, so everyone will be different. 

 

Spark Plugs

The spark plugs are what ignite the fuel and air mixture in the combustion chamber. They’re subject to all of the heat and compression created by the engine and can only withstand that for a certain period. You’ll experience hesitation, misfiring, loss of power, and a loss of fuel economy. If it’s awful, you might even see a check engine light appear. BMW recommends a plug change every 60,000 miles. That interval is perfect for stock engines running OE parts. However, there are more things to consider when the boost is turned up.

Spark plug choice is a reasonably hotly debated subject in the N55 world. Stock engines should keep the OE Bosch plugs at their specific heat range. However, modified engines should look at other options and service intervals. The easiest options for engines running tuned software with more boost are the plugs from the M3/4. They're one step colder in heat range and are designed to withstand the increased power from the engine. Look to change plugs every 35,000 miles instead. The interval will vary depending on the engine’s modifications, so keep an eye and ear out for signs of worn spark plugs. 

 

Ignition Coils

The spark plugs aren’t the only component of the ignition system that needs to be changed. Sitting atop the plugs are the ignition coils, the components designed to take the battery’s voltage and shoot it through the spark plug at just the right time. Several different companies produce these coils, such as Eldor, Bosch, and Delphi, though it seems the latter has the best track record on the N55 engines. 

Failing ignition coils will present symptoms identical to worn spark plugs. A failing coil means an ineffective plug. Swap the ignition coils between cylinders to determine if they are what’s causing your engine problems. Engines running stock power levels with stock components should see their coils last around 60,000 miles. Modified power levels won’t affect the coils as much as the plugs, but they will cut down on their life. Expect the replacement interval to shorten to around 40,000 miles with the extra strain on the engine. 

 

Fuel Injectors

The N55 did away with the troublesome Piezo-style injectors used by the N54. In their place are a set of solenoid-style injectors made by Bosch. While they are more reliable, failures occur, so you or a technician must replace them. Very early on in the N55’s production, BMW switched between injectors, only changing the parts used to secure them to the cylinder head.

The early injectors, used in engines built before January 2011, use hold-downs that secure it towards the bottom. Their injector well, the location in which they sit, is a two-piece design, utilizing a non-T-shaped hold-down. The later engines are secured right at the top, just below the fuel line connection. Their wells are a single piece, and the hold-downs are a T-shaped design. Use this tool to remove the early injectors and this tool for the later injectors.  

 

BMW N55 Modifications & Tuning

The N55 has gotten some knocks for not being as tunable as its predecessor, but that only makes sense concerning the N54. As its own entity, the N55 is very receptive to modifications. It’s a modern turbocharged engine with direct fuel injection and all the valvetrain goodies to support more power; BMW knew what they were doing when they put the N55 together. With all of the standard bolt-on performance bits and a piggyback tuner, you’re looking at around 375-400WHP. Here’s what you’ll need to get there and beyond. 

 

Intake

Many modern intake systems are designed only with packaging in mind. They feature sharp bends and edges that disturb the air, making airflow more turbulent and restricted. At the end of the intake tubing is an airbox that houses the air filter. The initial air intake happens through a small hole in that airbox. Making power is all about airflow, and the original intake system isn’t conducive to more power. Case in point, the M2 uses the same airbox as the 335i but has an additional hole cut in it for less restriction. You can use the M2 airbox as an OE upgrade, but the results will be minimal. Your best course of action is to move to an aftermarket system. 

Look around for an aftermarket option, and you’ll find plenty of attractive options out there; short-rams, carbon fiber intakes, some with airboxes, and some without. So which should you choose? Well, there isn’t much of a power differentiation between them, so grab the one that fits your budget or looks best. Dinan, one of the oldest American BMW tuners in the game, offers a carbon fiber intake with a larger diameter pipe, a larger filter, and a larger airbox to pull from. One of the more popular options right now is that from Burger Motorsports. That intake ditches the factory airbox for a heat shield that seals against the hood. The large reusable filter sits in the stock location and still draws cold air from the driver’s side grille. 

Regardless of who you end up with, there won’t be a considerable increase in power, around ten horsepower at most. There will be a more significant effect when paired with other modifications, but the main benefits are the increased sound and the different look. Look elsewhere for more impactful gains.

 

Exhaust

Turbochargers need to breathe, and unlike normally aspirated cars, they don’t have to worry about exhaust scavenging or back pressure. More flow means more power in this situation, so many of the aftermarket exhaust setups will have an enlarged pipe diameter over OE. Many of the better exhaust systems are going to be made from stainless steel as well. That metallurgy allows them to withstand the elements of any environment. Three-inch tubing made of T303 or T304 stainless steel will offer the best results for a mid-priced system. With those specs, you’ll get around a peak power bump somewhere in the teens and around the same in torque. Of course, you’ll see the best results once the DME has been tuned for the increased exhaust flow. 

Some of the companies to look out for here are AWE Tuning, Remus, and Supersprint. Those guys are well known and respected for the quality parts they produce and the exhaust notes they make. The most inexpensive exhausts will be the “axle-back” type. Essentially a higher-flowing muffler with increased sound. Add on the matching aftermarket mid-pipe section, and you have a “cat-back” system. The cat-back system will deliver increased performance over the axle-back due to the increased diameter of the mid-pipe over the original exhaust. Whether you choose one or the other, an aftermarket exhaust works best when used with other products designed to increase flow over OE. 

 

Downpipe

When talking about aftermarket exhausts, the downpipe is rarely included, and that’s because the downpipe is usually sold on its own. The downpipe is the first piece of the exhaust after the turbocharger and contains the catalytic converter, an expensive bit of platinum fitted inside the exhaust to make it less harmful to the environment. Many states require a catalytic converter in place, as do the ECUs of any N55-powered BMW. A downpipe with a high-flow catalytic converter is the best way to stay legally compliant while increasing performance. 

They aren’t cheap pieces of kit, but their benefits outweigh the cost. The factory cats are dense and restrict flow to produce the cleanest air possible. The aftermarket pieces are usually 200-cell units, around a third of OEM density, and prioritize flow over cleaning the air. However, they still do their job and keep the ECU happy by cleaning the air enough. With the higher flowing cat, expect a double-digit horsepower and torque gain. Fabspeed, Active Autowerke, and VRSF, among others, all offer catted downpipes that will increase performance and work with aftermarket exhaust systems. 

 

Intercooler

One of the keys to power is the amount of air being pushed through the engine; more air means more fuel. But that air isn’t always the same. As science goes, cooler air is denser than hot air. The flow can be the same, but the colder air carries more oxygen. Turbochargers are naturally very hot from their constant connection to the exhaust, and the air they force into the engine suffers from that heat. Manufacturers use intercoolers to combat that heat soak; they're heat exchangers designed to cool the charge air, making it denser. The colder the air and the faster it can move, the more power you can make.

The N55 uses an air-to-air intercooler mounted in front of the radiator. Its position on the front of the BMWs means it has constant exposure to moving air used to cool the charge air produced by the turbocharger. Aftermarket intercoolers, such as those from Wagner Tuning, CSF, and Evolution Raceworks, all use thicker cores with larger frontal surface areas to increase the flow they can handle and increase their cooling efficiency. Many aftermarket companies claim an increase of 15-20 horsepower at stock boost levels, depending on the supporting modifications. Expect bigger gains if you already run a raised boost pressure. 

 

Turbo Kits

Bigger turbochargers are where it all starts to get very expensive and can go wrong if you don’t have the correct supporting modifications. Once you’ve added on the standard bolt-on components, a bigger turbocharger is the next step. Typically you’ll find that retailers differentiate the turbochargers by “stages.” Stage 1 offers a mild increase, stage 2 is significant, and stage 3 is for a full-drag car build. The first two stages work best for the street and offer distinct levels of performance based on how crazy you want to get. 

Stage 1 kits offer a relatively stock turbo utilizing a larger compressor wheel made from a billet and modified compressor housing to deliver a modest bump in peak power and a whole lot more under the curve. The stock turbocharger tends to run out of steam around the 5500rpm mark, but modified stage 1 turbos have shown they produce and carry up to 75 more wheel horsepower around 1000rpm higher in the rev range. With full bolt-ons, expect around 450whp. 

If that isn’t enough, try a stage 2 kit. These turbochargers may retain the original look of the stock turbo but with internals primed for larger power output. For example, the Pure Turbos Stage 2 kit utilizes a larger compressor wheel, a higher-flowing turbine, and a ported manifold. Larger thrust bearings and dual oil seals on the hot and cold sides ensure that the turbo can withstand the extra performance demanded by the N55. With their recommended, higher-flowing inlet pipe, the stage 2 kit promises 500+whp when combined with the other bolt-ons. If you’re looking for more out of your N55 than a stage 2 turbo kit can offer well, it might be time to start looking at stronger pistons and cylinder head modifications. 

 

Tuning

Tuning is what makes everything come together. The mapping BMW put onto the stock ECU is meant for decent power while keeping the engine happy and healthy, well inside its tolerances. You can bolt on as many parts as you want, but without either a flash tune or a piggyback tuner to get the ECU to take full advantage of the increased flow and cooling capabilities of the aftermarket parts you’ve installed, you’re leaving significant performance on the table. 

You have two options for tuning your N55; you can either flash the ECU like the services from ESS or Dinan or go with a piggyback tuner like the Burger Motorsports JB4. Currently, the JB4 tuner is all the rage, and it's easy to see why. The JB4 plugs right into the ECU without any special tools or procedures. Once up and running, the tuner works seamlessly with the steering wheel controls and digital dash to allow you to choose different maps while driving. It also has a built-in code reader/deleter, can adjust for E85 on the fly, and will connect to your phone via Bluetooth so you can use it as a data logger or to update its firmware. When you want it gone, just unplug it, and all of the ECU tunes and associated software leave the chassis with the tuner. Without it installed, a dealership is none the wiser that it was there. 

Flash tunes offer similar performance for similar money. However, they cannot be easily removed and are only flashed software. What you get for your money is just a bump in performance. For the same money, the JB4 offers more protection and the same performance. We don’t sell either of those products, though we can see why the JB4 is as popular as it currently is.

 

BMW N55 FAQ

Is The BMW N55 Engine Reliable?

Even in the most encompassing terms, yes, the N55 is a reliable engine. During its evolution from the N54, BMW addressed some of the key areas where improvements needed to be made. Even inside the engine block, BMW changed castings, added cooling passages, and modified the oiling system to make the N55 a better engine. With that said, it isn’t perfect. The N55 still suffers from the classic oil filter housing and valve cover oil leaks that most BMW straight-six engines fight. The cooling system with its electric water pump can be a pain to deal with too. But overall, there are mostly just maintenance items to worry about here. Keep up with that maintenance, and the N55’s reliability should never be in question.

 

What oil type for the BMW N55?

There are a few factors that go into choosing the right oil for your N55. As shown above, there are several variations of the N55, with some pushed harder than others. Generally speaking, the garden variety M0-spec N55 will use 0w30 or 5w30 synthetic oil. O0 and T0-spec engines should run 0w40 or 5w40 for the extra bit of protection that the thicker viscosity brings to the table during increased demand from the higher-performance engine. With that said, you can run the thinnest 0w30 to the thickest 5w40 in any of the N55 engines without an issue. 

The thickness of the 5w40 works best in engines in hot climates or those pushing out significant horsepower. The colder the climate, the better it is to run the thinner 0-weight oil. Whichever viscosity you choose, ensure that it meets BMW’s Longlife-01 or Longlife-01 FE standard. Also referred to as LL-01, it's a specific set of standards BMW created for oils capable of running in the N55, among others. We’d recommend the LIQUI MOLY Special Tec or MolyGen for your next oil change, though just about all of the LIQUI MOLY oils meet the LL-01 standard. Some LIQUI MOLY CeraTec wouldn’t hurt, either.

All of the N55 engines run the same oil capacity, 6.5 liters, or 6.9 U.S. quarts. We offer several kits for the N55 engine that include the requisite amount of oil along with a new filter and the necessary O-rings to seal the filter’s cap. These are all covered by FCP Euro’s Lifetime Guarantee, too, making any future oil change worry-free. 

 

What coolant type for the BMW N55?

Sticking with the OE BMW coolant is your best bet. It’s inexpensive and readily available at any dealership. The coolant itself is nothing special; it’s the same stuff used in all of BMW’s engines. Find something with a “European Car Specification” if you have to buy aftermarket. Something like the Zerex G-48 spec is exactly what the N55 calls for. 

Before pouring in the coolant, know what is in the bottle. Modern antifreeze needs to be mixed in a 50/50 combo with distilled water to properly cool the engine. BMW sells just the coolant in a bottle, so you’ll have to mix it yourself before pouring it in. 


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Written by :
Christian Schaefer

Owner of a flat-six swapped 1998 Impreza 2.5RS and a 1973 Porsche 914. Horizontally opposed views, only.


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