BMW N54 and N55 Six Cylinder Turbocharged Engines

N54 with airbox removed to show filters.

Chronology

The N54 launched in 2006 as an option for the E90 three series to fill the gap between the 330i and M3. It's basically a twin turbo version of older the M54 3.0 and not related to the Valvetronic N52.

Initially power was 306bhp until an increase to 326 for the 2009 F01 740i, X6 and 135i. The most powerful 340bhp version only saw service in the E89 Z4 2010 on) and E82 1 series //M Coupe (2011 on).

The N54 was succeeded by the N55 from 2009 depending on model, so both were in showrooms side by side for a few years. Unlike it's predecessor the new engine used to a single turbo design.

For 2011 the version used in the 640i, 740i and M135i received a 12bhp power increase to 315bhp. After 2010 various models went to 322bhp in a confusing sequence and then to 335bhp for 2013. These changes almost certainly not uniform across all markets.

The range of power figures is due to varied boost pressures, fuel rail pressures, DME programming, intake and exhausts on different models. Frankly much of it can be taken with a pinch of salt as real world tests have shown these engines often make more power than rated. Many will have been re-chipped by owners to give even more.

N55 in a three series Active Hybrid.

Design

The N54's block is based on the M54B30 but with some major modifications, it's a two piece design with a bed plate to add stiffness. The cylinder liners are cast iron. It doesn't use the magnesium core technology of the N52. Also a different crankcase breather / oil separator method is used to prevent the higher vacuum pressures drawing oil into the intake. This engine uses a high specification forged steel crankshaft. Unlike the M54 an electric water pump is used to reduce parasitic losses.

Double VANOS is used but not Valvetronic as it's of less benefit to turbocharged engines. Valvetronic would also make it more awkward to fit the direct injection system used on this engine.

The twin parallel turbos are a low-inertia model from Mitsubishi so as to spin up quickly and reduce turbo lag, each feeds three cylinders. Boost ranges from 8.5 to 14.5psi depending on load and year of production. The DME controlled waste gates can run partially open so as to only use a fraction of the available turbo boost and ensure smoother power delivery.

The N55's block is similar but not identical to the N54's, the main difference is in cooling arrangements. The crankshaft is a lighter cast version, not forged anymore. Many engine parts are lightened and the valve train inertia is a good deal lower as a result.

Valvetronic control is applied to the N55 and the main advantage is improved throttle response combined with a better spread of power and torque. It also improves economy slightly, which was very welcome in such a powerful engine. Emissions are up to 15% lower than the N54.

The other big change is the replacement of the twin turbos with a single Borg Warner unit producing a lower 9psi maximum boost. Confusingly BMW still call these "Twin Turbo Power" engines. The gas flows are managed to ensure the best performance is obtained from each cylinder so less boost goes further than before. The new technology is called Cylinder-bank Comprehensive Manifold (CCM).

The N54 is commonly thought to have more potential to produce power than the N55 which is more of an attempt to create similar power with lower emissions.

The F87 M2 uses the 365bhp N55B30T0 rather than the S55 found in the M3 and M4. Compared to the normal N55 it gains oil-scavenging pickups to improved lubrication under hard cornering. It also uses the pistons and crankshaft main bearings from the S55. The block is now a closed deck design but not the same as the S55.

A 2006 N54 with airbox in place.

Variants

Code	Size	Power bhp@rpm	Torque lb/ft@rpm	BHP/ litre	Torque/ litre	Made	Bore x Stroke	Timing	Weight (kg)	VANOS	Used in
N54	3.0	306 @ 5800 326 @ 5800 340 @ 5900	295 @ 1300-5000 330 @ 1300-4500 330 @ 1300-4500	102 109 113	98.3 110 110	2006-13	84x89.6	Chain	195	VANOS, non Valvetronic	335i, E60 535i
N55	3.0	302 @ 5800 315 @ 5800 322 @ 5900 335 @ 5800 365 @ 6500 355@5800	295 @ 1200-5000 332 @ 1300-4500 332 @ 1300-4500 332 @ 1300-4500 343 @ 1400-5560 343 @ 1350-5250	101 105 107 112 122 118	98.3 111 111 111 114 114	2009 on	84x89.6	Chain	195	VANOS, Valvetronic	335i 535i 640i M2 X4 M40i

 

N54 showing carbon build up on intake valves.

Problems

These engines generate a lot of heat and need a cooling system that can keep up. Especially in hot countries that isn't always the case and after market radiator conversions were produced to help. Changing the coolant every two years is good practice for any engine but especially so for these.

On the N54 there is a problem with the turbo waste gate mechanism which resulted in US law suits and a TSB (technical service bulletin). Slack in the actuator rod can cause premature wear of the bypass valve and rattling. This can generate a fault code and cause the engine to enter limp home mode. Any engine should be checked for play in the waste gate actuator linkage.

A more common problem lies in the high pressure fuel pump (HPFP) needed for the direct injection system. In some countries BMW replaced them under a recall and / or extended the warranties. If a car takes a long time to start it may be due to a bad pump.

Many of these engines will have been re-chipped by owners to make more power. That's not a bad thing, but beware of any that have been pushed a bit too far.

As with other direct injection engines the valves can accumulate carbon deposits on the back and this can greatly reduce intake flow, even in a forced induction engine. The only solution is to remove the intake manifold and walnut blast the carbon off, crazy. Even after 40,000 miles substantial deposits can form.

These engines really should have had an oil cooler. If you plan on doing ANY track driving you need to fit one.

You MUST regularly check the oil level, any oil starvation at all is going to get expensive very quickly. Don't even think of running the oil for the recommended service duration if you value your turbo. Change it sooner, use the best oil and replace the filter half way through the cycle. Buying one of these with no service history is asking for trouble.

Fitting an oil catch can rather than using BMW's oil separator is highly recommended and there are many after market options. It can be cheaper in the long run and boost reliability.

These are complex engines that generate a lot of heat and need to be looked after. For most folk a non-turbo 3.0 is a cheaper option, if you want the extra power the running costs of an //M3 or //M5 will be similar. If you want the power for towing get a diesel. They will cause fewer problems in colder countries, far more in hotter countries such as the USA - this seems to be common to many modern BMW engines.

If an engine sounds very clattery it can be due to air in the hydraulic valve lifters. This can happen if the oil level falls very low or the car is used for nothing but very short trips, I've seen it once. The solution is to bleed the lifters. Warm the engine up with a short drive then with the car stationary run the engine at 3500rpm for three minutes, this can be tried several times back to back if needed. Certainly worked for me.

The valve cover is held on by single use aluminium bolts. On my N52 three had snapped and needed drilling out. Needless to say this caused an oil leak.

The oil filter housing gasket can leak causing an oil and sometimes coolant leak. It can be changed without removing the intake manifold but it's a wee bit tight.

The VANOS check valves on the side of the engine silt up with age, one of mine was filthy. Cleaning them resulted in may more mid-range power. Access via the wheel arch.

The DISA flap(s) can fail resulting in significant mid-range power loss.

The eccentric N55 Valvetronic shaft position sensor can fail and become filled with oil. Easy to check by removing the wiring connector.

The N55 Valvetronic motor's gasket can leak oil, not hard to fix.

The worst thing you can do to this engine is not change the oil often enough.