What’s the Difference Between the N54 and N55

So, you’ve been sitting around wondering what are the differences between the BMW N54 and N55 engines.  Well, I am happy to say that together we can look at what changed between these two engines.  I won’t cover everything, but the major differences and what that means to you.

What has remained the same

• Displacement remains unchanged with a total displacement of 2,979 cc utilizing a 84 mm bore and a 89.6 mm stroke
• Compression ratio is unchanged at 10.2:1
• Use of an air-to-air intercooler for charge air cooling
• Open deck block design with an aluminum block and iron cylinder sleeves
• Both are still direct injected, but with a change in injectors on the N55

Now the Fun Stuff, What Has Changed

• Most significantly is the use of a twin-scroll turbocharger on the N55 instead of the parallel twin to help improve turbo response and reduce turbo lag.  BMW has seen 15% improvements in fuel economy and lower emissions with this more efficient setup.
• The addition of 3^rd Generation Valvetronic.  Valvetronic is BMW’s name for variable valve lift which allows for precise adjustment of valve lift and duration.  This adjustment allows for improved efficiency across various engine operating conditions.
• Crank and connecting rods are now cast compared to forged in the N54.  However, the N55 crank is 3 kg lighter.
• Diverter valve is changed to an electronic actuator from the pneumatically actuated found in the N54. 
• The fuel injectors were changed to the Bosch solenoid valve fuel injector (HEDV5.2) from the piezo style HPI injectors found in the N54.  This change was primarily driven by cost and reliability issues outweighing the lean-burn advantages of the piezo style.
• VANOS (BMW’s variable valve timing system) is retained but the adjustment ranges are increased on the N55.  The N55 sees an additional 15 degrees of adjustment on the intake side, and 10 degrees on the exhaust.
• Engine operations are now controlled with the MEVD17.2 ECU from the MSD80/81 found in the N54.
• Additional webbing has been incorporated around the cylinder sleeves for improved cooling.
• N55 has a lower emission output by approximately 20%
• There were also various improvements to cooling, oiling and integration of a blow-by pipe on the crankcase ventilation system.

For the most part you can see that the N55 is really an evolution of the N54 engine.  From a performance standpoint the N55 outperforms in stock form, but the N54 seems to be a better and easier tuning platform.  This is primarily a result of the differences in rotating assemblies and the capability of N55 turbo setup.

Regardless of what BMW engine you have under the hood, remember at Alex’s Autohaus we are always here to help you with BMW repairs, maintenance and performance upgrades. Give us a call at (801) 566-6115 to discuss what we can do for you.