Tuning and modifying the N55

"Thanks for reading our N55 tuning guide"

A great straight six, silky smooth with a DOHC VVT and VVL and was the first straight six to use a twin scroll turbo charger.

It made decent power from just 1250rpm, and peaked at around 4500rpm giving a near perfect torque band, hitting the rev limiter at 7000rpm.

Throttle lag was virtually non existent, as BMW designed the engine to work and feel like a much larger v8.

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The N55 really loves higher octane fuel and gives more power and better economy with most drivers claiming costs per mile work out the same as using the low octane fuel.

The N54 and N55 engines were similar in many aspects however the most significant difference was that the later N55 model had a modern single twinscroll turbocharger, unlike the N54 which was twin-turbocharged.

History, Power & Specs of the N55 Engine

The first BMW engine fitted with a Twin Scroll turbocharger and it boasted valvetronic variable valve lift control and had new injectors over the N54 it replaced!

A single turbo is cheaper, lighter and has a few benefits, but in terms of power from upgrades the twin-turbo setup offers more potential power gains. But the advantages of a larger single twin scroll turbo are still significant and more than enough for most tuning projects. Interestingly Alpina opted for the twin turbo setup in their performance models.

Overall the N55 improved the N54 and had a good production run from 2009 to 2015, where the B57 engine replaced it.

Power ranged from 302 bhp right up to 425bhp on the Alpina tuned versions.

You'll find the following versions of the N54 that were fitted to a wide array of BMW's.

N55B30M0

  • 2009–2017 F10/F11/F07 535i
  • 2010-2013 E90/E91/E92/E93 335i
  • 2010-2013 E82/E88 135i
  • 2010–2017 F25 X3 xDrive35i
  • 2011-2013 E70 X5 xDrive 35i
  • 2011–2015 F30/F31 335i
  • 2011–2014 E71 X6 xDrive 35i
  • 2012–2015 E84 X1 xDrive35i
  • 2013–2016 F32/F33/F36 435i
  • 2014–2018 F15 X5 xDrive 35i
  • 2014–2019 F16 X6 xDrive35i
  • 2014–2016 F26 X4 xDrive 35i

Alpina BiTurbo

  • 2013–2017 Alpina F30 B3 Bi-Turbo
  • 2013–2017 Alpina F33/F34 B4 Bi-Turbo
  • 2017– Alpina F30/F31 B3 S Bi-Turbo
  • 2017– Alpina F32/F33 B4 S Bi-Turbo
  • 2018– Alpina F32/F33 B4 S Bi-Turbo Edition 99

N55B30 

  • 2011–2018 F06/F12/F13 640i
  • 2012–2013 E82/E88 135is
  • 2012–2015 F20/F21 M135i
  • 2012–2015 F01 740i/Li

N55B30

  • 2013–2016 F22/F23 M235i
  • 2015–2016 F20/F21 M135i LCI

N55HP

  • 2013–2015 F30 ActiveHybrid 3

N55B30T0

  • 2015–2018 F26 X4 M40i — 265 kW (355 bhp)
  • 2016–2018 F87 M2 — 272 kW (365 bhp)

Best N55 Upgrades & Mods

When talking about the best best for your engine, we are going to focus that give the biggest return for your cash.

Altering your camshaft will make a dramatic difference to the engine bhp. Choosing a higher performance camshaft profile raises the bhp accordingly.

Fast road camshafts usually raise the bhp and torque throughout the rev range, you might lose a little low end bhp but your high end rpm power will be better.

Race camshafts, raise the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

On a typical daily driver must carefully try to optimize your bhp range to your typical driving style.

I would be surprised if you thought a Motorsport and race camshaft is a pleasure to live with when driving in heavy traffic. The low end idle will be very lumpy and irregular, so something you would notice on a track when you drive in the upper third of the rpm band, but on roads this is a serious issue and we've heard from lots of drivers lamenting their decision to add an extreme competition cam profile to their engine.

Each engine responds better to more or less aggressive cam durations so set your engine up on a rolling road.

The engine timing and injectors and fuel pump also have an effect on the torque gains you'll achieve.

Extending exhaust or intake durations can alter the torque band and on most engines the exhaust and intake durations do not need to match, although most cams and tuners use matched pairs there are some advantages to extending the intake or exhaust durations.

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Best mods for your N55

  1. Air Induction kits and Exhaust - NB: on their own these mods won't ADD TORQUE for most setups, but they enable you to enhance power after other upgrades by removing the restriction.
  2. Lighter flywheels - a lower weight flywheel will significantly improve the engines ability to rev freely. In some cases flywheel lightening is not a great mod for all N55 engines.
  3. Flowing and porting the Head - Head work will get air flowing into the engine while removing turbulence or restrictions.
  4. Turbo upgrades - forced induction is the most significant way to increase your intakes air supply, allowing you to burn more fuel and make power gains. Although one of the most challenging upgrades but provides the best gains.
  5. Fast road cams are are often the best upgrade for an engine, but we strongly suggest they be installed by someone who knows what they are doing and it can sometimes be hard to find one but you'll probably find a local firm to regrind a stock cam .
  6. Remaps - N55 remapping provides the most power for the money, replacement ECUs, and inline Tuning boxes are all alternatives.

N55 Tuning Stages

Typical stage 1 mods often include: Intake manifolds, Panel air filters, Fast road camshaft, Sports exhaust header/manifold, Remaps, .

Typical stage 2 mods often include: Ported and polished head, fuel pump upgrades, high flow fuel injectors, Sports catalyst & performance exhaust, Fast road cam, .

Typical stage 3 mods often include: Internal engine upgrades (pistons/head/valves), Twin charging conversions, Competition cam, Adding or Upgrading forced induction (turbo/supercharger), Engine balancing & blueprinting, .

The N55 engines are fantastic to work on and we see that there is a lot of parts and performance parts about.

N55 Remapping

Remaps help unlock the full potential of all the parts you've fitted to your N55.

There are two types of mapping options:

  • Piggybacks
  • Flash Tuning or Remaps

Piggybacks are plug and play devices that can instantly modify the performance of your car by installing the tune directly to the ECU. Piggybacks work by altering the signal sent to the car’s computer. They bolt in and can be easily removed so are favored by many.

(In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it set up properly.)

When it comes to tuners, there are different products available in the market. The major products include:

  • Procede Rev3
  • TDI Tuning
  • Cobb Accessport
  • JB4

However, no other company has been able to even stand a chance against JB4, they have dominated the market for the 335i. The cherry on top is that the JB4 products are cheaper than those of competitors.

Depending upon the maps and the supporting mods you’ve done for your car, expect to see a horsepower increment of 60 to 80 hp with these tuners.

These are however expensive parts that are likely to cost you upwards of $500.

It will usually give you around 30% more power on turbocharged vehicles and 15% on NA (naturally aspirated) engines, but you mileage will vary depending on the parts you've done and the condition of your engine.

N55 Air intake mods and induction kits

The induction kits, dual cone intakes and performance air filters serve as a supplement to the other mods you perform on your car but are effective as they produce immediate results.

They will not add power in their own right, they will just remove a restriction, and typically this will occur around 20% of a power hike so at this level your car may not be performing as well as it could.

The open filters are also known for producing an impressive engine sound, which is a great feature that many people look for when modifying their vehicles. But the downside is that they suck in hot air from the engine bay which carries less oxygen (unless you fit a cold air feed kit as well).

Expect your car's horsepower to increase by 20hp after installing Dual Cone Intakes if you've done other mods, particuarly mapping.

Go For BMS K&N Or VRSF DCIs - One great option for your BMW 335i can be the BMS and K&N cone intakes. Or you can also go for VRSF.

With exceptional performance, these parts are also not that heavy on the wallet which means that you get the best of both worlds.

Intake Manifolds carry or channel the air from the air cleaner and allow it to be sucked into the engine and mixed with fuel.

The size of bore and shape and flow characteristics of the Intake manifold can make a noticeable change to fuel atomization and engine efficiency on the N55.

Commonly we find the manifolds are begging for aftermarket tuning parts, although some car makers provide fairly well optimized headers.

Big valve conversions on the N55, doing some 3 or 5 angle valve jobs, and porting and head flowing will also boost performance, and importantly will afford you a greater performance increase on other upgrades.

N55 Turbo upgrades

The more air to get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes massive power gains.

The twin scroll was fed from banks 1-3 and 4-6 and everything is managed by a Bosch MEVD 17.2 ECU.

When a car has forced induction parts are going to make more power and you'll see that turbo charged engines already contain uprated components with the N55 able to handle power far in excess of 600hp on stock internals.

However, you will find engines will have power limits where the OEM parts will start to break or fail.

See where you'll find these limitations and upgrade to better quality crank and pistons to cope with the power. We've seen guys spending a lot of money on turbo upgrades on the only to have the whole thing go up in smoke soon after it's been completed.

Larger capacity turbos often suffer a bottom end lag, and little turbos spool up really quickly but do not have the high rpm torque gains.

Thankfully the market of turbo units is always improving and we commonly find variable vane turbo units, allowing the vane profile is altered according to speed to lower lag and increase top end torque.

Twin scroll turbo units divert the exhaust flow into two channels and direct these at differently angled vanes in the turbocharger. They also increase the scavenging effect of the engine.

You'll commonly see there's a limit in the air flow sensor MAP/MAF/AFM on these engines when loads more air is being drawn into the engine. Going up you'll find 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor limited bhp and torque at a much lower level.

Adding a supercharger or additional turbo will make large bhp and torque gains, although more complex to install. We have a twincharger bhp and torque adding guide if you want to read more.

N55 Fuelling Upgrades

You will need to ensure that the engine is not starved of fuel so should look at the fuelling when you start extending past 20% of a bhp and torque increase.

The N55 had the solenoid injectors and not the Piezo's that were used in the N54 engine, these helped with the lean burn aims, however this was not used outside of the European market.

We strongly recommend you to be generous with your injectors flow rate. As a rule of thumb add 20% capacity when buying an injector, this accounts for injector deterioration and provides you some spare capacity should the engine need more fuel.

Intake Manifold Port Injection Kit

For around $1849 you can get yourself the Intake Manifold Port Injection Kit from “Evolution of Speed” which includes:

  • Intake manifold with integrated fuel rails
  • Quick connect fittings
  • 6 fuel injectors
  • Fuel hose to fit into the existing fuel system

It can be helpful to address fuel starvation issues and can allow you to run alternative fuels and grades of fuel that have better knock resistance.

Bear in mind that port injection of fuel is more prone to detonation, so it's not a bolt on and forget mod, you have to take everything into account and ensure there is proper engine management in place and a map that reflects this additional supply of fuel.

N55 Exhaust upgrades (headers and catback)

Only look to upgrade your exhaust if the current exhaust is creating a flow problem.

Ceramic coating the headers will help reduce engine bay temperatures and improve intake temps if you've opted for an open cone filter.

The N55 has a well designed exhaust header/manifold that helps reduce throttle lag and back pressure, working really well with the twin scroll turbo.

On most factory exhausts you'll see your flow rate quite well even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Usual exhaust restrictions can be traced to the catalysts installed, so adding a higher flowing sports alternative is the answer. This keeps the car road legal and will flow much better due to its higher internal surface area and design, so has the added benefit of keeping your car road legal. The alternative decat should be considered an off road only mod, as removing a catalyst is illegal in most territories and regions for road registered cars.

Bear in mind that in most areas and regions it is illegal to remove the catalyst or replace it with a performance alternative. Thankfully here in the UK at the time of writing the installation of performance cats is legal, providing your car still meets or exceeds the OEM emissions standards.

Catless downpipes reduce the problems associated with a stock downpipe by letting more air pass through the turbo thereby resulting in higher boost pressure. Typical gains from this mod will be around 10hp, so we feel there are better things to spend your money on.

Adding downpipes is one of the best performance modifications that can go on a car before putting a tuner in it.

Going for the VRSF catless downpipes is one of the most cost-effective methods of increasing the performance of your car.

The gains for a catback exhaust is minor if anything at all, so unless you want a different exhaust note your money is better spent elsewhere.

Weakspots and problem areas on the N55

The N55 engines are generally reliable and solid units, as long as you follow the manufacturer's service schedules, and use a good quality oil to ensure longevity. Few problems should happen as long as they are regularly serviced and maintained.

Carbon build up issues on the N55

Carbon build-up in the head, particularly around the valves which will sap power or create flat spots, this is a larger issue on direct injection engines but should be looked out for on all engines. We have tips on removing carbon build up.

Flat spots or lumpy idle problems after tuning upgrades

Some of our members have had issues with flat spots or glitches after applying mods and upgrades or tuning, this is not usually related to the design of this engine, so instead see our article on diagnosing flat spots and problems after tuning which should help you get the bottom of this issue.

Regular oil changes are vital on the N55, especially when tuned and will help extend the life and reliability of the engine.

N55 PCV crankcase valve problems

Oil consumption issues have been noted, due to a PCV crankcase valve.

N55 Injector problems

Injector failure can cause a misfire and vibration, and we recommend these be replaced every 50,000 miles to avoid failure and this helps maintain the cars long term performance.

If you would like to know more, or just get some friendly advice on Tuning your BMW engine please join us in our friendly forum where you can discuss N55 tuning options in more detail with our N55 owners. It would also be worth reading our unbiased BMW tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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