Legendary straight-six engines like the Toyota 2JZ, Nissan RB26, Ford Barra, and even the BMW N54, have all been up on a pedestal and they’re like the best engines ever. Previously we’ve made a video covering BMW N54 and what makes it so special, but eventually, the N54 was replaced by the N55, so today we’re going to dive in and tell you everything you need to know about the BMW N55.
In 2006 when BMW dropped the N54 it was their first mass-produced turbocharged engine. Previously BMW had produced turbocharged engines in the past such as the M102 and M106, but those engines were limited production and never had successors. BMW had a long history of producing excellent naturally aspirated engines, so the N54 was a huge change for BMW.
Not too long after the N54 was released in 2006, BMW began implementing the N55 in 2010 in the 5-Series Gran Turismo. Compared to the N54, the N55 had a significant amount of changes that were designed to make it more reliable, because the N54 did have a substantial amount of problems. While the N54 was BMW’s first mass-produced turbocharged engine, the N55 was their first engine to use a twin-scroll turbocharger.
To cover some basic information, the BMW N55 is an all-aluminum 3.0L straight-six engine with dual overhead cams, variable valve timing, and variable valve lift. Bore measures at 84mm and stroke at 89.6mm. This brings the total displacement up to 2,979cc. This is the same displacement, bore, and stroke as the BMW N54 before it, and it also features the same 10.2:1 compression ratio.
As far as applications go the N55 was used in the 135i, 335i, 535i, X1, x3, x5, 640i, 740i, M235i, and more. It was used in pretty much everything BMW offered, from small coupes up to large SUVs, which is a testament to how versatile this engine is. Depending on the specific model you’re looking at, power output ranges from 302hp and 295lb-ft ll the way up to 365hp and 369lb-ft.
I know some of you might be thinking that 302 to 365 horsepower out of a modern 3.0l turbocharged isn’t much, and you’d be right. It’s not that much considering the displacement and turbocharged nature, but it’s what’s on the inside of the N55 that matters, and at the end of the day BMW wasn’t trying to build some crazy record-breaking engine. They just wanted to improve on the N54 and give their cars a great engine.
Working from the top down, let’s take a closer look at the cylinder head first. As stated earlier, the N55 is an all-aluminum engine which means the cylinder head is constructed from cast aluminum. Compared to cast iron, cast aluminum heads are much lighter and offer superior thermal performance which is important because the cylinder head is a big determining factor in how much power your engine makes.
The valvetrain is comprised of dual overhead cams driven by a timing chain, with four valves per cylinder. Pretty standard stuff for a modern engine.
One of the big changes BMW made when going from the N54 to the N55 is the addition of its Valvetronic system. Both the N54 and N55 use BMW’s VANOS system on both the intake and exhaust camshafts, but only the N55 uses the Valvetronic system which allows for variable lift control.
Having variable valve lift and variable valve timing is a huge performance benefit in terms of power and efficiency. It can make tuning a little tricky if you don’t know what you’re doing, but overall the Valvetronic system is a great addition to the N55.
Bolted to the side of the head, you’ll find the Twin Scroll single turbocharger manufactured by Borg-Warner. Not too surprisingly, the OEM turbo is pretty small. Small turbos provide great throttle response and a ton of low-end power, which is something you want for a streetcar. I know there are videos of 1000hp Supras taking forever to hit their boost threshold and that seems cool, but trust me in the real world you want something much more responsive.
Without getting into too much detail, a twin-scroll turbo can provide better throttle response and increased boost pressure compared to a single scroll turbo. The reason BMW ditched the twin-turbo system on the N54 for the single turbo system on the N55 isn’t totally clear, but single turbo systems are cheaper to manufacture, easier to package, more thermally efficient, and they provide better reliability.
Moving down to the block, it’s constructed from cast aluminum and features an open deck design. Theoretically, the open deck design is a limiting factor when making big power, but for the large majority of street cars, the block is more than strong enough. If you want to upgrade your block there are several closed deck conversions on the aftermarket.
Inside the block, BMW unfortunately “downgraded” from the N54 with its forged internals to the N55’s cast internals. This is something that you should take with a grain of salt because although forged internals uses a superior material, the design of the internals also plays a big part in their strength.
Unfortunately, no engine is without its faults and the N55 is no different. BMW did fix many of the issues found on the N54, but there are still common problems with the N55. One of the more unreliable parts on the N54 and the N55 is the electric water pump. While these have significant advantages over mechanical water pumps, they do break quite a bit more.
Another common issue you’ll find is high-pressure fuel pump failure, but that’s mostly a problem on older models. The VANOS solenoids are also known for failing prematurely, and on 2010 through 2012 engines the VANOS bolts were known for breaking and/or coming loose.
As far as tuning potential, you can pretty easily get the N55 up to around 400whp and 473wtq with bolt-on parts and a tune. That’s with a pretty aggressive ethanol tune though. If you want more, there are some hybrid turbo options on the market if you want something nearly as responsive as stock while also increasing power.
Obviously, if you want big power you’re going need either a big single or twin turbos. At that point, you’re going to be limited by the bottom end at around 500 to 550whp. If you’re wondering, yes the N54 bottom end is stronger and can handle more power, but that’s something which we’ve already gone into in previous articles.