Tuning · BMW M135i (F20 / F21)
M135i
N55
The N55 hot-hatch sleeper in F20/F21 form. Hand-calibrated from Stage 1 through to hybrid and big-turbo builds.
Engine
N55
Stock
322 bhp · 450 Nm
Stage 3 ceiling
322 bhp
About this tune
The F20 / F21 M135i (2012-2016) is the pre-LCI 1 Series hot hatch, N55 single-turbo straight-six in the smallest possible body. Stock is 322 bhp / 450 Nm (BMW Performance Power Kit trim), sent rear-wheel via the ZF 8HP. Available as the F20 5-door and F21 3-door, both sharing the identical drivetrain. The N55 predecessor to the B58 M140i, and one of the most popular N55 tuning chassis in the UK.
BMW M135i tuning
Rear-wheel drive in a five-door hatch body is a combination BMW no longer sells, which is exactly why the F20/F21 M135i (2012-2016) has become a cult buy. It looks like the school-run 1 Series, costs sensible used money, and hides M Performance hardware underneath. Owners tune it because the chassis was always capable of far more than the badge suggested, and because no modern rival offers this layout at the price.
From the factory the M135i makes 322 bhp and 450 Nm. Samuel's Stage 1 lifts that to 380 bhp and 500 Nm on completely standard hardware for £400, filling in the mid-range where the factory map holds the car back. Stage 2, with a downpipe, intake or panel filter and an uprated intercooler, moves the hatch on to 420 bhp and 550 Nm — supercar pace in a body the size of a Golf.
The platform runs much deeper than that: with a B58 TU fuel pump the Stage 2+ file reaches 440 bhp and 600 Nm, and hybrid or full-frame turbo conversions take the M135i towards its 800 bhp ceiling. Everything happens remotely — you flash through the OBD port using bootmod3, MHD or MG Flasher, Samuel delivers your calibration within 24 hours, and the original BMW file is kept so the car can go back to stock whenever you want.
Configurator
Build your M135i tune
Choose your stage — Stage 1, Stage 2 or Stage 3 — add the options that fit your car, and send the full build to Samuel for a custom remote remap. He'll quote, schedule, and personally calibrate within 24 hours of confirmation.
Add a stage or add-on
£0
Engine guide
BMW M135i tuning, stages, hardware and what to expect from the F20 N55
The F20 / F21 M135i (2012-2016) is the pre-LCI 1 Series hot hatch, the N55 single-turbocharged 3.0-litre straight-six in the smallest possible body. From the factory, BMW set the M135i at 322 bhp / 450 Nm (BMW Performance Power Kit trim); the hardware ceiling sits considerably higher and is shared with the rest of the N55 family. BMW M135i tuning with Samuel applies the same N55 Stage 1 / Stage 2 / Stage 2+ map family used on the 335i, 435i and M235i, same engine, same MEVD17 DME, same hardware ceiling.
Stage 1
380 bhp · 500 Nm
No hardware required. The MEVD17 DME is flashed via the OBD port. BMW M135i Stage 1 unlocks 380 bhp and 500 Nm from the OEM hardware (up from 322 / 450 stock). The BMW M135i chip tuning starting point and the most cost-effective change you can make to the F20 / F21 N55 hot hatch.
Every M135i tune Samuel produces is calibrated individually for the specific car, fuel grade and installed hardware, not a base map loaded and left. BMW M135i tuning done correctly accounts for the F20 chassis behaviour, the gearbox calibration and UK fuel quality; the map is reviewed against your data logs after the first flash and revised before sign-off.
Compatibility
Platform and hardware compatibility
Bootmod3 (BM3)
Full N55 support across every chassis in the family (M135i, M235i, 335i, 435i, 535i, 135i, X3 / Z4 35i, M2 N55). MEVD17 DME OBD flashing, realtime monitoring via the BM3 app. One of the most mature N55 tuning platforms.
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MHD
Full N55 support, historically the dominant platform on the N55 before BM3 caught up. Suitable for Stage 1, Stage 2 and Stage 2+. Excellent data-logging toolset.
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MG Flasher
Full N55 support. Clean interface and reliable flash process on the MEVD17 DME. A common alternative to BM3 / MHD for owners who prefer the MG ecosystem.
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xHP Flashtool
Compatible with the ZF 8HP gearbox fitted to F-series N55 cars (M135i, M235i, 335i F30, 435i, 535i, X3 35i F25). Strongly recommended at Stage 2 and above. E-series N55 cars (135i E82, 335i E90 / E92 / E93, Z4 35i E89) use the ZF 6HP automatic or a 6-speed manual, xHP does not cover those gearboxes in the same way.
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ECU: MEVD17.2 DME across most N55 production. Accessible via OBD port for Stage 1, Stage 2 and Stage 2+; bench-flash only required for some Stage 3 hybrid setups.
M135i specs & stage targets
BMW M135i tuning at a glance
- Engine
- N55
- Body styles
- F20 5-door · F21 3-door
- Chassis codes
- F20 / F21
- Production
- 2011–2019
- Drivetrain
- Rear-wheel drive
- Gearbox
- 8-speed ZF automatic
- Stock output
- 322 bhp · 450 Nm
- Tuning ceiling
- ~800 bhp on the right hardware
| Stage | Target |
|---|---|
| Stage 1 | 380 bhp · 500 Nm |
| Stage 2 | 420 bhp · 550 Nm |
| Stage 2+ | 440 bhp · 600 Nm |
| Stage 3, Hybrid Turbo | Up to 800 bhp depending on spec |
| Stage 3, Big Turbo Kit | Up to 800 bhp depending on spec |
FAQ
M135i tuning — frequently asked questions
It moves the F20/F21 from 322 bhp and 450 Nm to 380 bhp and 500 Nm using only the factory hardware, for £400. The gain is felt mostly through the mid-range, where the standard calibration is at its most conservative, and the file is flashed at home through the OBD port on bootmod3, MHD or MG Flasher.
Three things: a downpipe, an intake or upgraded panel filter, and a better intercooler. With those fitted, Samuel's Stage 2 calibration runs the standard turbo to 420 bhp and 550 Nm. The factory fuelling copes at this level; the B58 TU fuel pump only becomes necessary at Stage 2+, where the target rises to 440 bhp and 600 Nm.
Usually, yes — the N55 was built for sustained boost and many tuned examples carry big mileages. Before flashing, make sure the basics are honest: recent spark plugs and coils, no pending fault codes, a healthy cooling system. Samuel keeps torque targets within the hardware's designed limits, so a well-maintained car is not being pushed anywhere unsafe at Stage 1 or Stage 2.
Tell Samuel what you actually fill up with and the calibration is built around it. Super unleaded of 97-99 RON is the sensible choice for the full Stage 1 and Stage 2 figures, because the higher octane lets the N55 hold ignition timing cleanly. If you can only get 95 RON locally, say so — the map is adjusted rather than left marginal.
Few cars match it. Used F20 and F21 prices are modest, the £400 Stage 1 lands 380 bhp, and the engine is the same N55 fitted to the original M2. Insurance, parts and running costs are all 1 Series rather than M car, yet the tuned output sits firmly in modern M territory.
Keep exploring
Keep exploring M135i tuning
Other N55 models we tune: M2 (N55), M235i, 135i, 335i, 335i (E90), 435i.
Engine guide
N55 tuning
Every N55 BMW we calibrate, with the full Stage 1, 2 and 3 breakdown for the engine.
Learn moreStages
Stage 1 & Stage 2 explained
What separates Stage 1 from Stage 2 on the M135i, the real-world gains and the hardware each one needs.
Learn morePricing
How tuning is priced
How the licence, off-the-shelf maps and custom calibration are priced. We quote your exact spec, never a fixed menu.
Learn moreGuide
What is bootmod3?
New to remote flashing? A plain-English explainer on the platform and how a custom map reaches your car.
Learn more