Modified BMW M135i for Sale in the UK
The BMW M135i remains a cult favourite among UK enthusiasts. Featuring BMW's N55 turbocharged straight-six engine producing 316bhp in standard form, the M135i offers serious tuning potential inside a compact and practical hatchback. Its combination of RWD dynamics, strong engine, and available xDrive all-wheel drive has earned it an enthusiastic following in the modified car community.
Modified BMW M135i models for sale often produce 380–450bhp through a combination of ECU remapping, hybrid turbo upgrades, chargepipe replacements and supporting bolt-on modifications. Rear-wheel drive F20 examples are particularly desirable for their balanced handling characteristics, while xDrive-equipped models offer traction advantages for high-power street builds.
On Madlows, you'll find UK-listed modified M135i models from private sellers and specialist dealers, each with detailed modification descriptions. Whether you're looking for a clean, tastefully modified daily driver or a full track build, browse live M135i listings and contact sellers directly through the platform.
The M135i's combination of practicality, tuning potential, and relative affordability in the used market makes it an intelligent choice for enthusiasts who want genuine performance without the insurance premiums of a full M car. The N55 engine is well-understood by tuners across the UK, and the aftermarket support is extensive — from off-the-shelf stage 1 tunes to bespoke hybrid turbo builds with custom mapping.
Modified BMW M135i Listings
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List your M135i todayPopular BMW M135i Modifications
The N55 engine and ZF gearbox combination supports a wide range of modifications. Below are the most common upgrades seen on modified M135i models sold in the UK.
Engine & Tuning
- • Stage 1 & Stage 2 ECU remaps (360–420bhp)
- • Hybrid turbo upgrades (EFR, GTX range)
- • Upgraded chargepipe (known weak point)
- • High-flow intercoolers
- • Catless downpipes
- • Performance exhaust systems
Handling & Styling
- • LSD retrofits for RWD examples
- • Coilover suspension (KW, Bilstein)
- • Suspension lowering springs
- • M Performance body styling
- • Upgraded braking systems
- • Aftermarket alloy wheels
BMW M135i Buyer's Guide
When evaluating a used modified M135i, there are several specific checks to carry out beyond the standard used car inspection.
Rod Bearing Health
The N55 engine's rod bearings can wear on high-mileage units, particularly where oil changes have been neglected. Listen for any knocking or rattling from the engine at idle and under load. Ask for evidence of rod bearing replacement or inspection — this is a critical check on any N55 with over 70,000 miles.
Turbo Condition
Check for turbo shaft play and signs of oil leaks around the turbo housing. On hybrid turbo-equipped cars, ask who carried out the installation and whether the oil feed lines were upgraded. Proper oil supply is critical for turbo longevity on modified N55 engines.
Chargepipe Integrity
The factory chargepipe on the N55 M135i is a known weak point and prone to splitting on higher-boost applications. Check whether the car has an aftermarket chargepipe upgrade — this is a common and recommended modification for any tuned M135i. Inspect for any signs of boost leaks under the bonnet.
Cooling System
Higher-power M135i builds generate more heat and place greater demand on the cooling system. Verify that the coolant has been changed on schedule, the thermostat is functioning correctly, and check for any signs of coolant leaks around the expansion tank and hoses — common wear items on older N55 engines.
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Frequently Asked Questions — Modified BMW M135i
Is the N55 engine reliable when tuned?
The BMW N55 is a well-built turbocharged straight-six and responds well to tuning when maintained correctly. Key areas to monitor include rod bearings, which can wear prematurely on high-mileage engines, and the cooling system, which benefits from an upgraded thermostat and radiator on higher-power builds. A properly tuned N55 with regular oil changes and supporting modifications is generally reliable up to around 400–420bhp.
What is the average power of a modified M135i?
A stage 1 ECU remap on the N55-powered M135i typically raises output from the standard 316bhp to around 360–380bhp with good torque improvements across the rev range. Stage 2 builds with an upgraded turbo, intercooler and downpipe can achieve 400–430bhp. Full hybrid turbo conversions with supporting fuelling upgrades have been known to push beyond 450bhp on the N55 platform.
Are M135i modifications expensive to insure?
Insuring a modified M135i can be more expensive than a standard car, but specialist insurers such as Adrian Flux, Footman James and Greenlight offer tailored policies for modified vehicles. Costs depend on the extent of modifications, your age, location and no-claims history. Always declare all modifications — undeclared changes can void your policy in the event of a claim.