Both the N54 and the N55 are remarkable engines produced by BMW, but which of the two should you choose if you had the chance? What are the differences between the BMW N54 vs N55?
Although there are several differences between the N54 and the N55, the most significant of all boils down to the turbochargers they use. The N54 comes with true twin turbochargers. Meanwhile, the N55 uses a twin-scroll turbo. A twin-scroll turbo is a single turbocharger with exhaust housing that splits into two scrolls.
Read on to learn more about the differences between the BMW N54 vs N55.
Origins of the BMW N54 and N55
We will be discussing which of the two engines is better in a bit. For now, let’s learn about how they came to be.
Before 2006, BMW focused mainly on building naturally-aspirated engines. Of course, the Bavarian carmaker made turbocharged engines before, like the M102 and M106. However, those engines did not have successors. It was not until the N54 did BMW come up with a mass-produced turbo engine.
The N54 engine was developed at the same time as the N53. Both of them are part of the NG6 engine family of BMW. A couple of vehicles used this engine. However, just after 5 years after its release, BMW already phased it out. It was replaced with the N55 except for a couple of cars.
Both the N54 and the N55 have all-aluminum block 3.0L inline six-cylinder engines. They are featured in BMW sedans and sportscars. Moreover, both engines won the International Engine of the Year awards.
N54 and N55 Turbochargers
The biggest difference between these two award-winning turbocharged engines is exactly that, their turbochargers. The N54 uses actual twin turbos. Meanwhile, the N55 uses a single turbo with a twin-scroll exhaust.
N55’s Twin-scroll Turbocharger
If you are unfamiliar with a twin-scroll turbocharger, it is a standard turbo inside. However, its exhaust housing is split into two. It looks like a standard, but when you look inside the housing, there are two chambers.
The benefit of twin-scroll turbos is that every bank of the three cylinders that fire on the same cycle will have its scroll from the turbo. This minimizes exhaust reversion.
The twin-turbo and twin-scroll setups of the N54 and N55 (respectively) provide the following:
- Excellent throttle response,
- Minimal input lag if any, and
- A wide powerband.
The N55, with its twin-scroll setup, can reach its top torque output 100rpm sooner than its predecessor. However, you will not notice this when both are on the road.
On the other hand, when modified, the twin-turbo N54 outperforms the N55 with the same mods. This is because the N54 can move significantly more air, so it gets more benefits from mods.
With that said, twin-turbo setups like the N54 are significantly more complex, larger, and more expensive. It is the reason why car tuners prefer single-turbo setups. They are easier to mod for more power.
However, the N55 has 15% more improved fuel economy and lower emissions because of its more efficient turbo setup.
Other Differences Between the N54 vs N55
Other than the turbochargers, there are many more changes between both engines, mainly:
1. Inclusion of a 3rd-gen Valvetronic
Valvetronic is the in-house variable valve lift used by BMW. This system allows for precise valve adjustments and durations. This feature provides improved engine efficiency across different operating conditions.
2. Crank and Connecting Rods
The N55’s crank and connecting rods are all cast and not forged like in the N54. On the other hand, the N55’s crank is 3kg lighter than that of the N54.
3. Diverter Valve
The diverter valve in the N54 is a pneumatic actuator. Meanwhile, the N55 uses an electronic one.
4. Fuel Injectors
The fuel injectors in the N55 were changed to the ones using the Bosch solenoid valves from the piezo-style HPI injectors that the N54 used. The reasons for this change are primarily cost and reliability, even though the piezo-style does burn leaner.
5. BMW’s Variable Valve Timing System
BMW’s variable valve timing system, known as VANOS, remained. However, it has more adjustment ranges in the N55. The N55’s VANOS has an additional 15 degrees of adjustment on the intake and 10 degrees on the exhaust side.
The ECU also changed from the MSD80/81 in the N54 to a MEVD17.2.
7. Additional Webbing
There is also additional webbing incorporated around the N55 cylinder sleeves to improve their cooling.
8. Emission Output
The emission output of the N55 is 20% lower in the N55 compared to the N54.
9. Small Improvements in Engine Cooling and Lubrication
Several small improvements are also noticeable in engine cooling and lubrication – Also, there is an added blow-by pipe in the N55’s crankcase ventilation.
What Remained the Same Between the N54 and N55?
Although the N54 and the N55 are essentially different engines, a lot remained the same. These include the following:
- The displacement of both engines is the same at 2,979cc and use 84mm and 89.6mm stroke.
- The compression ratio of both engines is the same at 10.2:1.
- Both use an air-to-air intercooler to cool the charge air.
- Both have an open deck block design, billet aluminum blocks, and cylinder sleeves made of iron.
- The two are direct-injected, but the fuel injectors of the N55 are a bit improved.
N54 vs N55 – Which Is More Reliable?
The N55 is the more reliable engine between the two. The N54 was the first mass-produced turbocharged engine by BMW, so it may be fair to say that the N54 was a sort of an experimental product at the time.
Especially during the first couple of years of production, the N54 was plagued by many issues, which convinced most BMW owners to avoid the engine.
BMW recalled certain cars that used the N54 engine and offered many extended warranties because of its somewhat unreliable nature. We will be discussing these issues in more detail later.
BMW got most of the issues from the N54 resolved in the N55. However, the newer engine also has its quirks (more on this later). In hindsight, all gearheads agree that BMW is not known for building super reliable engines. These two engines do live up to the company’s reputation of making the ultimate driving machines.
Again, what’s the main difference between BMW N54 vs N55? The main difference between BMW N54 and N55 is their turbochargers. While the N54 has true twin turbochargers, the N55 uses a twin-scroll turbo. This twin-scroll turbo refers to a turbocharger equipped with an exhaust housing capable of splitting into two scrolls.
BMW N54 Common Issues
If you have always been a BMW fan, you probably already know that their cars are notorious for repairing issues. Here are some of them:
1. Water Pump Issues
The N54 engines use electronic water pumps instead of the traditional belt-driven mechanical water pumps used by older model cars. Although the electronic water pump has many benefits over a traditional mechanical pump, it does not last quite as long. You can expect to have your water pump replaced every 60k to 80k miles.
2. Carbon (Soot) Buildup in Cylinders
Due to the N54 using direct fuel injection, the engine enjoys perks like increased power and fuel efficiency. However, it creates a lot of carbon buildup on the intake valves.
In engines that use multi-port fuel injections, gasoline is constantly shot into the cylinders. Because gasoline is a great solvent, it cleans the intake valves automatically. On the other hand, direct injection valves will not get into contact with gasoline ever. Carbon byproducts coming from the combustion chamber will eventually cover them.
Carbon buildup can cause throttle lag, poor fuel economy, cylinder misfires, and significant loss of power.
3. High-Pressure Fuel Pump Breaking
Another common problem in the N54 is HPFP failure. Some symptoms caused by HPFP failure include engine stutter and loss of power. It may even cause the engine to stall and not be able to restart.
4. Fuel Injector Malfunction
Another common issue in N54 engines is fuel injector failure. BMW already revised its design 10 times. However, they still managed to fail. You may experience the main symptoms when the fuel injector fails, including engine misfires and a significant loss of power.
5. Oil Filter Housing Gasket Cracking and Leaking
The oil filter housing gasket in the N54 is prone to leaking. When this gasket leaks, it can cause oil and coolant to mix. This is especially true if the mentioned leak is internal. It can cause oil to spray all over the drive belt and its components if it is external. This can lead to severe damage.
6. Serpentine Belt Failure
In the 2007-2008 models, you can see the power steering pulley positioned a little too close to the subframe. As the motor mounts wore down over time, the engine would move ever so slightly when hitting corners hard.
This results in the pulley getting into contact with the subframe, thereby shredding the serpentine belt. This can potentially lead to catastrophic engine failure and a list of other issues.
7. Cracked Valve Cover and Gasket Leaks
In the N54 engines, the valve covers would usually crack, and the gasket would leak after some time. There have been reports of these two components failing just a little over 25,000 miles on the odometer.
You will know that this is the issue when you smell burning oil coming from the exhaust. Also, when you pull out the spark plugs, you will see pooled oil in the holes.
8. Rattling Turbo
This is one of the most common problems that the BMW N54 engine has. After some time, the wastegate arms would loosen quite a bit, thus causing the rattling sound.
Most of the time, this would only cause an annoying sound when you are lifting your foot off the throttle. However, it can also cause a boost-leak code. Eventually, the turbocharger will not create any boost.
BMW N55 Common Issues
The N55, although it is a bit more reliable compared to the N54, this BMW engine still has a couple of potential problems, mainly:
1. Boost and Charge Pipe Breaking or Detaching
Many N55 owners have experienced problems with the boost or charge pipes, sometimes both at the same time. The charge pipe connects to the throttle using a small clamp. This small metal clamp cannot withstand high-pressure boosts.
In certain cases, even the stock boost is enough to detach the hose. Expect this to happen when you have had a little too much fun with the car on the track or a wide stretch of road.
This same thing can potentially happen to the boost pipe, which connects directly to the turbo intercooler. However, when this happens, you will need to replace everything, including the O-ring seals.
2. Valve Cover and Gasket Leaks
BMW could not seem to fix these same leaks that usually happen in N54 engines. Also, this issue can cause the PCV (Positive Crankcase Ventilation) valve to crack, seeing as it is directly over the valve cover. When this happens, expect the engine to experience rough idling.
The PCV valve is essentially a diaphragm that extracts the blow-by gases within the crankcase. The usual reasons why PCV valves fail include high mileage or the engine getting too hot.
3. Water Pump Failure
Water pump failure is not exclusive to just the N55. This is a problem that most BMW engines have. The water pump will help to re-circulate coolant to cool down the engine after a long day of driving. The water pump that the N55 uses is electric. It is the same as the N54.
It also has a particularly short lifespan. Do not expect this to last over 50,000 kilometers. In addition to the water pump, you should also replace the coolant thermostat as it is notorious for failing sooner rather than later.
Conclusion – BMW N55 vs N54
The turbochargers are the most obvious differences between the BMW N55 vs. N54. The N54 uses real twin turbochargers. On the other hand, the N55 comes with a twin-scroll turbocharger. The twin-scroll turbocharger is just a single turbocharger. It has the added design improvement of splitting the exhaust housing into two scrolls.
Hopefully, this guide helped you a lot when choosing between these two iconic gasoline engines. Although the N55 engine is significantly better, there is no reason why you should avoid the N54 as it is also a good and mod-friendly engine in its own right.