The BMW N55 engine, a twin-scroll turbocharged inline-six, has earned a reputation for its blend of refinement and performance. Found in models like the 3 Series, 5 Series, and X1, the N55’s versatility has made it a favorite among enthusiasts seeking to push its limits. For those looking to elevate their driving experience, aftermarket performance parts offer a gateway to increased horsepower, improved handling, and a more engaging drive. Here’s a breakdown of the most impactful upgrades for the N55.
1. ECU Tuning: The Foundation of Power
The first step for many enthusiasts is ECU (Engine Control Unit) tuning. Devices like the Cobb Accessport or Dinan tunes reprogram the engine’s parameters, optimizing fuel delivery, ignition timing, and boost pressure. This can unlock significant gains—often adding 50+ horsepower and 70+ lb-ft of torque—without physical modifications. Tunes are customizable, catering to stock or heavily modified setups, and often include features like launch control and rev limiters.
2. Intake and Exhaust Systems: Breathing Easier
Upgrading the intake system allows more air into the engine, enhancing throttle response and power. Pairing this with an aftermarket exhaust system—such as cat-back or axle-back setups from Akrapovič or MBRP—reduces backpressure, amplifies the engine’s soundtrack, and can add a few extra horsepower.
3. N55 Air Intake
Unlocking hidden power in your BMW begins with improving airflow, making an N55 air intake one of the most popular first modifications. The factory airbox is designed for quiet operation, not maximum performance. A high-quality aftermarket intake system reduces restriction, allowing your engine to breathe more freely. This results in modest but noticeable gains in horsepower and torque, typically ranging from 10 to 12 wheel horsepower. Beyond the performance figures, installing an N55 air intake dramatically enhances the turbo and induction sounds, giving your BMW a more aggressive and sporty auditory character without the complexity of a full exhaust system.
4. N55 Cold Air Intake
While often used interchangeably with a standard intake, an N55 cold air intake specifically emphasizes thermal management. These systems are designed with a sealed air box or heat shield to isolate the air filter from the hot engine bay air. By drawing cooler, denser air from outside the engine compartment—often through a front-mounted scoop—these intakes maintain lower inlet temperatures. This is crucial for consistent performance, as cooler air prevents the engine computer from pulling timing due to heat soak. A well-designed N55 cold air intake ensures your engine makes its power run after run, providing both a performance edge and the satisfying sound of increased turbo induction.
5. N55 Catless Downpipe
For those chasing significant power, an N55 catless downpipe is arguably the most impactful bolt-on modification available. The stock downpipe houses a restrictive catalytic converter that traps heat and limits exhaust flow from the turbocharger. Replacing it with a catless version removes this bottleneck, allowing exhaust gases to exit rapidly. This reduction in backpressure allows the turbo to spool faster and more efficiently, leading to substantial gains in torque and horsepower, often cited as 10-20 wheel horsepower depending on tuning. As a critical component of any stage 2 build, an N55 catless downpipe requires a corresponding ECU tune to disable check engine lights and fully exploit the increased flow potential.
6. Intercooler Upgrades: Combatting Heat Soak
The N55’s stock intercooler can struggle with heat soak during prolonged use, such as on track days or spirited drives. Upgraded front-mount or bar-and-plate intercoolers from brands like Wagner or Cairott provide superior cooling capacity, ensuring consistent power output even under heavy load.
7. Transmission and Drivetrain: Handling the Power
For automatic transmissions, upgraded torque converters or clutch packs (e.g., from Sachs or ZF) improve shift firmness and durability. Manual drivers might opt for a lightweight flywheel for quicker revs. A transmission cooler is also wise for those tracking their car or driving in hot climates.
8. Suspension and Handling: Sharpening the Edge
To balance the increased power, suspension upgrades are essential. Lowering springs (Eibach, H&R) or coilovers (KW V3) reduce ride height and body roll, enhancing grip and agility. Upgraded sway bars and polyurethane bushings further improve chassis rigidity and responsiveness.
9. Cooling Systems: Staying Cool Under Pressure
Additional cooling solutions, such as upgraded radiators, oil coolers, or brake cooling kits, help manage the heat generated by increased performance. These are particularly beneficial for track-focused builds.
10. N55 Oil Filter Cap & N55 Magnet
Many versions, such as those from Burger Motorsports or Paradigm Engineering, also feature a powerful rare earth magnet integrated into the design. The factory oil filter cap is made of plastic and lacks any advanced filtration features. Upgrading to a billet aluminum oil filter cap with an integrated high-strength magnet captures microscopic ferromagnetic particles—tiny metal shavings from normal engine wear or bearing break-in—that would otherwise circulate through your engine. By trapping these contaminants before they can cause damage, an N55 magnet helps prolong the life of your turbocharger and rotating assembly. It also provides a visual indicator during oil changes, allowing you to monitor the metallic content of your oil and catch potential issues early.
11. N55 Port Injection
As you push your N55 beyond 500 wheel horsepower, the factory direct injection system can max out its fuel delivery capacity, risking engine damage from a lean condition. This is where N55 port injection becomes a critical upgrade. By adding a secondary set of fuel injectors in the intake manifold, port injection supplements the direct injectors, providing the massive volume of fuel required for high-ethanol blends like E85 on big turbo setups. Integrating this system with a flex-fuel kit and a capable ECU tune ensures precise fuel control. This not only safely supports extreme power levels but also helps keep the intake valves clean from carbon buildup, a common issue with direct-injection engines.
12. N55 Turbo Upgrade
A N55 turbo upgrade is the cornerstone of any serious power build for this platform. While the factory twin-scroll unit provides responsive daily power, it quickly becomes a bottleneck for enthusiasts seeking over 400 wheel horsepower. Upgrading to a larger aftermarket turbocharger forces more air into the engine, which, when combined with the correct fueling and tuning, translates to exponential power gains. Options range from “hybrid” turbos like the Pure600 that use modified factory housings for easier installation, to full-frame big turbo kits. Each N55 turbo upgrade path requires careful consideration of your power goals and supporting mods to ensure the engine reliably handles the increased stress.
13. Pure 600 N55
The Pure 600 N55 turbocharger represents a popular “middle ground” upgrade for those aiming for significant power without the lag of a larger 750 unit. Designed as a drop-in replacement with a new, better-flowing turbine housing, the Pure600 is engineered to efficiently support power levels in the 550-600 wheel horsepower range on ethanol blends, while still delivering strong performance on pump gas. It positions itself as an ideal choice for drivers targeting a responsive yet powerful 500 wheel horsepower on 93 octane, often hitting the N55’s octane limitation without the need for more complex and expensive fuel system upgrades required by larger turbos.
14. Big Turbo N55
For enthusiasts seeking a dramatic leap in power, a big turbo N55 upgrade is the ultimate path. Replacing the factory twin-scroll unit with a larger aftermarket turbo allows the engine to flow significantly more air, resulting in substantial horsepower and torque gains well beyond what bolt-on modifications can achieve. Options like the Pure600 or Dinan big turbo kits are engineered to provide this increased airflow while maintaining spool characteristics suitable for street driving. However, installing a big turbo requires supporting modifications; upgraded intercooling, fueling, and a professional custom tune are essential to safely manage the additional boost and heat, transforming your BMW into a high-horsepower machine.
15. N55 Top Mount Turbo Kit
For the ultimate power enthusiast, an N55 top mount turbo kit represents the pinnacle of performance modification. Unlike factory or hybrid turbos that sit low in the engine bay, these kits relocate the turbocharger to a visible position on top of the exhaust manifold. This setup accommodates much larger turbochargers, such as GT35 or even 6466 variants, capable of supporting over 700 wheel horsepower. While an N55 top mount turbo kit dramatically reduces the complexity of servicing the turbo, it demands a comprehensive suite of supporting modifications, including port injection, upgraded intercooling, and custom fabrication, transforming the vehicle into a high-horsepower machine built for serious straight-line performance.
16. N55 Turbo Inlet Pipe
Often overlooked in favor of larger intakes, the N55 turbo inlet pipe is a vital component for maximizing airflow efficiency. The factory inlet pipe is notoriously restrictive, featuring a narrow diameter and complex curves made of plastic. Upgrading to an aftermarket silicone or aluminum pipe, typically expanding the diameter to 3.35 inches, smooths and straightens the path for air entering the turbo compressor wheel. This reduction in turbulence and restriction allows the turbo to spool more quickly, reducing lag and increasing overall power. An N55 turbo inlet pipe is the perfect complement to a high-flow air intake, ensuring that all the additional air being pulled in actually reaches the turbocharger efficiently.
Strategic Upgrades for Maximum Impact
When modifying the N55, a strategic approach yields the best results. Start with ECU tuning and bolt-on upgrades like intake, exhaust, and downpipe, which offer significant gains with minimal complexity. As power levels rise, consider intercooler, transmission, and suspension upgrades to ensure reliability and handling match the engine’s output. Remember, combining parts synergistically—such as pairing a tune with intake and exhaust—maximizes performance. Always consult with professionals for installation, especially for complex modifications, and consider fuel octane requirements and warranty implications. With the right upgrades, the N55 can transform from a refined daily driver to a track-ready beast, embodying the essence of BMW’s performance heritage.
