Quick summary
- BMW swapped the twin-turbo N54 for the single-turbo N55 in the 2011 model year, with factory output untouched.
- The N55 uses one twin-scroll turbocharger and adds Valvetronic, reaching peak torque 200 rpm earlier than before.
- In the 335i the swap lifted EPA combined economy from 20 mpg to 22, with no change in output.
Short answer: the two engines make identical factory numbers and get there differently. The older one breathes through two small turbochargers; its replacement uses a single twin-scroll unit and adds BMW’s throttle-less valve control, which buys efficiency and slightly earlier torque. The reason enthusiasts still argue about them has little to do with stock output and everything to do with what each engine accepts afterwards.
What is the difference between the N54 and N55?
Hardware, mostly. The N54 carries two small turbochargers; the N55 carries one mid-sized turbocharger with a twin-scroll housing, which BMW adopted to keep response quick without the complexity of a second turbo. The N55 was also BMW’s first inline-six to combine turbocharging, High Precision direct injection, and Valvetronic — the throttle-less intake system that controls air inside the engine rather than at a throttle plate.
The output did not move. BMW quoted the same 300 hp and 300 lb-ft for both, with the N55 reaching peak torque at 1,200 rpm, 200 rpm earlier than its predecessor, and doing it with better fuel economy and lower emissions.
| Spec | N54 | N55 |
|---|---|---|
| Turbocharging | two small turbochargers | one twin-scroll turbocharger |
| Valve control | direct injection, no Valvetronic | direct injection plus Valvetronic |
| Output | 300 hp / 300 lb-ft | 300 hp / 300 lb-ft |
| Peak torque from | 1,400 rpm | 1,200 rpm |
| 335i EPA combined | 20 mpg (2010) | 22 mpg (2011) |
That last line is the clearest evidence that the change was about efficiency rather than power: the EPA rated the 2010 335i at 17 city and 26 highway, and the 2011 car at 19 and 28, with the same horsepower on the window sticker.
Which cars got which engine
The N54 arrived first, in the 2007 335i, and spread through BMW’s 35i models. For the 2011 model year BMW moved the 135i, 335i, 535i, 535i Gran Turismo, X5 xDrive35i, and X6 xDrive35i onto the N55. In practice, a US-market 335i built up to 2010 has the twin-turbo engine and one from 2011 onward has the single-turbo engine, which makes model year the quickest way to tell them apart before you open the hood.
Which one should you buy?
If the car is a daily driver, the N55 is the easier ownership story: one turbocharger instead of two, better economy for the same performance, and none of the high-pressure fuel pump history that followed the early N54 — the fixes worth doing before any tuning are laid out in our N54 build guide.
If the plan is power, the N54 is still the engine people choose, and the ceiling is the reason. Our look at how far the N54 has been pushed ends at a verified 9.54-second quarter mile, a figure the N55 tuning scene never chased in the same way.
And if neither story appeals — if the appeal of a BMW six is smoothness rather than boost — the naturally aspirated N52 sat alongside both of these engines in the cheaper cars, with a shorter list of expensive failures.
Sources: BMW USA press materials for the 2011 model year engine change (single twin-scroll turbocharger, Valvetronic, output, torque onset, models affected) and EPA fueleconomy.gov ratings for the 2010 and 2011 335i, October 2026. Photos: Zongxianglee (CC BY 4.0) and Pangalau (CC BY-SA 4.0) via Wikimedia Commons.
