M135i PRE-LCI (F20 & F21)

Most owners start with an aluminium charge pipe, because the factory plastic item on the N55 is prone to splitting once boost is increased. A Stage 1 remap usually follows. On the chassis side, quality coilovers or lowering springs, a front strut brace and a performance alignment make the biggest difference to how the car feels. Many also budget for a limited-slip differential, as the standard open diff struggles to put the power down out of slow corners.

The N55's charge pipe, between the turbo and the intercooler, is plastic and can crack at its seams or joints as it ages and as boost rises. When it fails the car loses boost suddenly and goes into limp mode. An aluminium charge pipe with stronger couplers is a straightforward, inexpensive upgrade and is widely recommended before any remap, but it is also a sensible preventative fix on an older standard car.

The N55 responds well to a remap. Stage 1 software on an otherwise standard M135i is commonly reported at around 360–380bhp, and owners with supporting parts such as an intake, charge pipe and sports-cat downpipe often quote close to 400bhp. Beyond that, the single twin-scroll turbo becomes the limit rather than the cast internals. Results depend on fuel quality, the map and the health of the car, so treat published figures as typical rather than guaranteed.

No. The M135i left the factory with an open rear differential, so under hard acceleration the inside wheel can spin and the electronics intervene. Fitting a limited-slip differential is one of the most popular upgrades on the car. BMW produced an M Performance LSD for the F2x range, and aftermarket plate-type units are also available. An LSD makes the car noticeably more effective on track and in wet or tight corners.

Generally yes. Lowering springs keep the factory adaptive dampers, so the comfort and sport modes still work, though ride quality becomes firmer and damper life can shorten with a large drop. Replacing the adaptive dampers with coilovers is different: the car will show a suspension fault unless a cancellation kit or coding is used. Always check that a spring or coilover kit is listed for adaptive-damper cars before ordering.

Many do. The F20, F21, F22 and F23 share much of their suspension, brakes, steering wheel and interior hardware, so springs, coilovers, braces and paddles are often listed for all four models. Engine parts differ because the M140i and M240i use the B58 rather than the N55, and bumpers, splitters and diffusers differ between pre-LCI and LCI hatchbacks. Each R44 product shows its fitment, and My Garage filters parts to your exact car.