Tuning and modifying the N55

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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.

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

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.

We rely on our visitors to pass on tips and tell us about their projects and what worked on their car, and this article is the culmination of the feedback we have received. First let us look at the history and specs of this engine and then consider which tuning modifications work best on it.

History 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!

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)

What are the most effective upgrades

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.

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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Modifying to Stage 1:

 Intake headers, Panel air filters, Fast road camshaft, Sports exhaust manifold, Remaps, .

Modifying to Stage 2:

 Ported and polished head, fuel pump upgrades, high flow fuel injectors, Sports catalyst & performance exhaust, Fast road cam, .

Modifying to Stage 3:

 Internal engine upgrades (pistons/head/valves), Twin charging conversions, Competition cam, Adding or Upgrading forced induction (turbo/supercharger), Engine balancing & blueprinting, .

Remaps helps unlock the full potential of all the parts you've done to your N55.

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

Pushing air into your is the whole point to any engine performance tuning task.

Headers carry 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 Headers can make a noticeable change to fuel atomisation and engine efficiency on the N55.

Commonly we find the headers 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 - which are best?

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.

NASP engines need quite a lot of work when you add a turbo, so we have a separate guide to help you take into account the pros and cons of going this route on your N55

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.

However you will find an engines will have power limits

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.

Fuelling

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.

N55 Exhaust

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

The N55 has a well designed exhaust 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.

Don't go with the widest exhaust you can buy this will slow the exhaust rate - the best for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Usual exhaust restrictions can be traced to the catalysts installed, so adding a higher flowing sports alternative will help avoid this restriction.

Weakspots and problem areas on the N55

The N55 engines are generally reliable and solid as long as they are regularly serviced and maintained.

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

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

Injector failure can cause a misfire, and vibration, and we recommend these are replaced every 50,000 miles.

For more information 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.

Please help us improve these tips by sending us your feedback in the comments box below.

We love to hear what our visitors have got up to and which upgrades work best for them on each model of car. Comments are used to improve the accuracy of these articles which are continually updated.

This article was written by Waynne Smith on TorqueCars, and I appreciate your feedback and suggestions. This entry was filed under BMW. You can leave a response below or join TorqueCars forum to discuss this article and car modification in detail with our members.

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