As you may already know, BMW’s modern turbocharged inline-six-cylinder engines are incredible. They provide 2JZ-like levels of performance, respond very well to modifications, and have strong aftermarket support.
Two of the most popular turbocharged BMW engines are the N54 and N55. They’re very similar and closely related, but there are some significant differences. Let’s dive and see which one is better!
Where They Came From
Before talk about which one is better, we should briefly cover the what these engines are and how they came to be.
Up until 2006, BMW focused on building naturally aspirated engines. They had produced turbocharged engines before 2006, such as the M102 and M106, but those engines never had successors. The N54 was BMW’s first mass-produced turbocharged engine.
The N54 was developed alongside the N53, and it’s part of BMW’s NG6 engine family. It was featured in a handful of different vehicles, but ultimately it was officially phased out for the N55 in 2011, except for the 1M and Z4 35i.
Both engines are all-aluminum 3.0L inline-six. Both are features in sports cars and sedans, and both have won International Engine of the Year awards.
Turbochargers
Arguably, the most significant difference between the N54 and N55 is the turbochargers. The N54 features twin turbochargers and the N55 uses a single twin-scroll turbo.
A twin-scroll turbo is just a standard turbo with the exhaust housing split into two scrolls. With this setup, each bank of three cylinders on the same firing cycle feed an individual scroll of the turbocharger which reduces exhaust reversion.
Ultimately, both the twin-turbo setup of the N54 and single twin-scroll setup of the N55 offer great throttle response, minimal lag, and a very wide powerband. The twin-scroll setup allows the N55 to deliver peak torque 100rpm sooner than the N54, but that difference is hardly noticeable in the real world.
The twin-turbo setup on the N54 does offer better performance when modified compared to the N55. Simply put, the N54 moves more air and will outperform an N55 mod-for-mod.
That being said, twin-turbos are more complex, take up more space, and cost significantly more. If you want to make big power, the twin-turbo setup is typically ditched in favor of a single turbo setup.
Reliability
Of course, the turbo setup is just one small part of each engine. Reliability is arguably the most important things to look for in an engine, and unfortunately, the N54 has horrible reliability.
As we’ve discussed in previous articles, the N54 has tons of problems with fuel injectors, high-pressure fuel pumps, electronic water pump failure, and other common problems.
It should be noted the N55 isn’t perfect, but BMW did fix many of the issues the N54. Common issues for the N55 include valve cover leaking, electronic water pump failure, high-pressure fuel-pump failure on older models, and VANOS solenoid failure.
Both engines suffer from waste-gate rattles, however, it doesn’t typically affect the longevity of the turbos.
To put it simply, the N55 is more reliable than the N54, but that’s not a hard thing to achieve considering the N54 was pretty unreliable.
I know there are going to people in the comments claiming their N54 or N55 is the most reliable thing in the world and has never broken down on them, but the reality is that both have pretty poor reliability, with the N55 being marginally better.
Engine Internals
When it comes to internal components, the N54 is arguably better. The N54 features a forged crank and rods, with the N55 features cast crank and rods. Both engines feature cast piston, and unless you’re looking to push north of 600whp, both bottoms ends are plenty strong.
If you want big power, a big single turbo is the most common setup. With a big single turbo, you can push both engines to around 600 to 700whp on a stock bottom end. Past that, both engines need aftermarket forged bottom end internals to survive.
Both engines are very similar in many aspects and stock-for-stock perform nearly identical. The N54 offers peak torque 100rpm sooner and slightly better throttle response, but it’s barely even noticeable in real-world driving conditions.
Summary
Both offer pretty poor reliability, with the N55 being slightly better. Thanks to the N54’s twin turbos and forged internals, it is the more capable engine mod-for-mod.
Realistically, they’re so similar in terms of performance, that you can’t exactly say one is better than the other. The N54’s forged internals are marginally stronger and the twin-turbo setup allows for a bit more power on the stock turbo setup, but the N55’s improved reliability makes up for any gaps in performance.
We think the N54 is marginally better, but not but much.