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The N55 M135i/235i is often overlooked compared to its newer B58 M140i/M240i counterparts. Whilst the B58 is known for becoming a monster with just a couple of easy mods whereas the N55 is considered less tuneable, which doesn't have to be the case. 


The driving point for this being the N55 engine is limited by its packaging, running a tiny intercooler similar to what's found in 4-cylinder models. resulting in a conservative quoted 320BHP and 450Nm. 

Because of this, we’ve worked on a simple hardware and software solution taking the N55 M135i/235i up to 420BHP 640Nm rivalling its B58-powered stablemates for both performance and character.



After a lot of R&D working on the platform, we found that the conventional STG1/STG2 packages didn't apply to the F20 135i/235i.

The key limiting factor on the N55 was that the stock intercooler is completely unchanged from the lesser models, the result of this was incredibly high intake temperatures.

Running a completely standard car on the dyno we observed 63-degree intake temperatures. When tested on the road the results were even worse! Road/track data logs showed a sustained 68-degree intake temperature over a 3rd, 4th and 5th gear acceleration despite the car having high-speed airflow.


Not only is the is detrimental for making power, but when used hard on track, the engine protection systems would limit power further due to the temperatures being too high even on the road. 

Our only option for managing these extreme temperatures was to explore intercooler options, we wanted some that offered an easy installation and OEM fitment, meaning a clean install, no body modifications, and the ability to revert the car fully back to standard with ease, should there be a need.


After conducting exhaustive research AIRTEC's N55 Intercooler fitted the bill of what we were looking for perfectly, substantially lowered intake temperatures, and offered easy fitment and OEM-like installation onto the F20 Platform. 

With an intercooler only, intake temperatures were more than halved compared to the stock cooler, with a peak of 28.5 degrees on the dyno and a staggeringly low 26 degrees on the road during the same sustained acceleration 3rd, 4th, and 5th gear pull.


With the engine cool, it was only right to make sure the rest of the hardware was up to the task, so we've also opted for cooler NGK Spark Plugs and an MMR panel filter. 


We also thought it was only right to sharpen up the gearbox to match the engine, that's why we've included XHP STG3 gearbox tuning as part of the Package! 

( you can also opt for XHP STG1 or STG2 if you prefer) 


As manual cars don't require gearbox tuning the package price is reduced to £1350. 


We’ve been tuning BMW engines for nearly 10 years now, and it’s no surprise we’ve become rather good at it. Everything is created completely in-house and custom tailored to the car and driver's requirements.

Our goal when tuning the N55 M135i/235i was to give the N55 that much-needed performance and excitement of a true M engine, without sacrificing any drivability or reliability you’d expect from a BMW. Whether you’re enjoying a B-Road blast on completing lap after lap of your favourite circuit your car is going to perform.



The results are 420BHP and 640NM ( Peak torque dependent on owner wishes), the most impressive aspect is not just the peak numbers but the way the car drives, torque is progressively fed in to help get the power down and get away from the spikey feeling. Peak power climbs to a new peak promoting you to hold onto the RPM long after the stock car plateaued and fizzled out.

This is the most effective way to transform the driving experience of your N55 M135i/235i into something you’d expect from a full-fat M car.


What's included?

- AIRTEC N55 Motorsport Intercooler ( all intercoolers are black with the option of AIRTEC logo) 

- MMR High Flow Panel filter 

- NGK NGK Iridium Spark Plugs 97506 SILZKBR8D8S

- XHP STG3 Gearbox Tuning ( £300 Price reduction for manual cars )

- Labour for Fitting 

- Running on Our In house dyno 

- TRS Custom Engine Tuning 



The total price for the TRS 420 Package comes in at £1650 for automatic cars and £1350 for manual cars. 

BMW M135i/235i TRS 420 Package

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