With impressive turbo power and virtually limitless modding potential, the N54 and N55 are modern-day performance legends – here’s our BMW N54 and N55 engine guide as we delve beneath the surface to see what these turbo powerhouses are all about.
Guide brought to you by Performance BMW. Words: Elizabeth de Latour. Photos: Larry Chen, Daniel Pullen, Zayne Smith, Mike Kuhn, Viktor Benyi.
BMW N54/N55 History
The N54 engine first appeared in the 2006 E92 335i and was introduced across the BMW range over the following three years. The twin-turbo straight-six arrived in 306hp form with 295lb ft of torque and this is the version that the majority of N54-powered cars have; the F01 740i and US-only E92/3 335is came equipped with a 326hp version, which also received 332lb ft of torque, while the most powerful version of the engine was that found in the E82 1M Coupé and E89 Z4 sDrive35is, which made 340hp, with an overboost function that gave it 369lb ft for five seconds at full throttle.
The N55 was introduced in 2009 and went from two turbos to a single larger one and both its power and torque figures were unchanged from the N54, but peak torque arrived 100rpm earlier. Unlike the N54, there were numerous different incarnations of the N55 as BMW fitted it to just about every model. The F-range 640i, US-only E82/8 135is, F20/1 M135i and F01 740i all received the 320hp version with 332lb ft; the F22/3 M235i and LCI M135i both got the 326hp version, while the F30 ActiveHybrid 3 had the 340hp N55. Finally, the F26 X4 M40i came with a 360hp version that also got 343lb ft while the F87 M2 came with the most powerful version of the engine, with 370hp and 369lb ft of torque.
Let’s get technical
The N54 and N55 share their internal dimensions with the engine they’re based on, the M54. This means that they have an identical bore and stroke (84×89.6mm), and the compression ratio is also the same at 10.2:1, which helps to explain why it feels like a normally aspirated engine in the way it drives as it’s not a low-compression motor. However, there are several big differences – the M54 is a closed-deck single-piece block whereas the N54 is an open deck design and consists of two pieces. The water pump is also electric on the N54 whereas on the M54 it’s cast into the front of the block. As well as this, the M54 uses a more traditional fuel injection method, whereas the N54 features direct injection.
The N54 uses two smaller turbos running at 8.8 psi in order to keep lag to a minimum, while the N55 uses one larger one, which features a twin-scroll compressor housing. This means that the exhaust side of the turbo is divided into two parts, each fed by three exhaust primaries. In addition to this, the N55 also comes equipped with Valvetronic variable valve lift technology, which improved throttle response and low-end torque as well as reducing fuel consumption by 15% and lowering emissions compared to the N54. The N55 also switched from the N54’s more expensive Piezo fuel injectors to solenoid-type ones, the former being deemed not worthwhile using any longer as markets outside of Europe could not benefit from their potential lean-burn benefits.
N54/N55 tuning potential
While the N54 and N55 are impressive performers in stock form, it’s when you start modding them that their true performance potential is realised. While both engines give good gains, the N54 will always make slightly more power simply because it has two turbos and that means it’s easier for it to generate more power. The good news is that you don’t need to spend a lot of money and you don’t need any complicated mods to see good gains on both engines – we’re going to be using the base version of each engine for reference because the more powerful ones already come pre-tweaked from BMW and so gains will vary on those.
Your first port of call will be either a remap or a tuning box and there are plenty of options for both and they’ll both result in similar gains. A remap will get you an increase of around 60hp and 80lb ft, while a tuning box like a JB4 or bootmod3 will get you up to 80hp, and with a lot of tuning boxes being incredibly easy to install there’s really very little effort involved in getting a substantial hike in power, and at around £450 it’s a very cost-effective performance mod. On naturally aspirated engines intakes don’t generally offer much in the way of gains, but on a turbocharged car they’re always worth a look and while an intake won’t do a whole lot on its own (apart from giving you some more induction noise, which is never a bad thing), once you start throwing more mods at your N54 or N55, it all adds up. There are loads on the market to choose from but the BMS one gets good reviews and is definitely worth a look, and it costs about £130.
The charge pipe (the pipe from the intercooler to the intake manifold) on both engines is flimsy and can fail even at stock boost pressure, so once you start upping the power an uprated one is an absolute must. For the N54 we’d look at the Rennessis pipe from SSDD (£200), which comes complete with an uprated blow-off valve, or the VRSF item (£200) for your N55. An upgraded blow-off valve is an important addition because once boost pressure increases the stock ones can leak – the N54 uses manifold absolute pressure (MAP) so is quite happy with either a recirculating or an atmospheric blow-off valve, while the N55 uses a MAF sensor and so it’s best to stick with a recirculating one (our turbo tech guide in the May issue explains why).
The most restrictive point of both the N54 and N55 exhaust systems is the downpipe. On the N54 you have one of these from each turbo, and on the N55 there is just one and it’s the cat in each of these pipes that causes the restriction and a massive increase in back-pressure. Fit a de-cat downpipe and you instantly gain power, torque, improved throttle response and more noise, so they’re an absolute win all-round and you can expect to pay around £400. The rest of the exhaust is fine and any changes won’t really make a difference to power, but they will give you an awesome straight-six soundtrack to enjoy, so we’d throw one on for that reason alone. We’d also look at adding an uprated intercooler to help keep intake temperatures down, thus potentially increasing power, and one from someone like Mishimoto will set you back about £600.
At this point, you’ll have around 400hp+ on an N55 and 420hp+ on an N54, and for most people that’s going to be enough; it won’t have cost you a fortune to get to this point and your car will feel very quick indeed. Of course, there’s always more you can do and the next step would be a set of hybrid turbos with uprated internals. It’s about £2500-3000 for a pair of hybrids for the N54 or around half that for one for the N55 and that will get you well over 500hp, potentially even over 600hp, on an N54 and around 470hp+ on an N55. You will need some additional supporting mods such as an even larger intercooler, uprated low-pressure fuel pump on the N54, and potentially even meth injection to help keep intake temperatures down and prevent detonation. If you still want more you need a big single-turbo setup and for that, you’ll need a manifold, which will set you back around £2500-3000 and then you need a turbo plus additional mods, so the costs will start to rack up but you can hit over 700hp.
