M135i X Drive / M-Sport (F40)

Most owners start with sound and feel. A GPF-back exhaust, such as Scorpion's system for the F40, gives the B48 a far more characterful note while keeping the factory particulate filter. An induction upgrade, aluminium paddle shifters and lowering springs are also popular early changes. If you drive quickly or plan track days, uprated brake pads and fresh high-temperature fluid are worth doing before adding power.

Generally no. A GPF-back system replaces the exhaust after the factory particulate filter, so the engine's emissions hardware and sensors are left in place and the car runs on standard software. The main gains are sound and a small weight saving rather than significant power. Changes further upstream, such as sports-cat downpipes, normally need a matching calibration to run properly and should be discussed with a tuner first.

Stage 1 software on the F40 M135i is widely documented at around 350PS and 530Nm, up from the standard 306PS and 450Nm, though results vary with fuel quality, tuner and conditions. The strengthened B48 copes well at this level, but the eight-speed automatic and front Torsen differential are the parts to respect, so choose a calibration from a reputable tuner that manages torque sensibly in the lower gears.

Yes, provided you choose springs designed for it. MMX lowering springs for the F40 M135i drop the car by around 25mm at the front and 20mm at the rear and are made to work with both the standard and adaptive M suspension. Have the alignment checked after fitting. For full control over ride height and damping, a coilover from KW or BC Racing is the alternative.

Many do. The F40 M135i and F44 M235i Gran Coupe share the same platform, B48 engine, eight-speed gearbox and xDrive system, so engine, brake, suspension and interior parts are often common to both. Body-specific items such as splitters, side skirts, diffusers and exhausts usually differ because the bodywork is not the same. Check the fitment listed on each product, or save your car to My Garage to filter compatible parts.

In the UK, fitting aftermarket parts does not automatically void a manufacturer warranty, but a dealer can refuse a claim for a failure it links to the modification, and engine software is often detectable. Bolt-on parts such as brakes, springs and exhausts are usually less of a concern than remaps. Always declare modifications to your insurer, as undeclared changes can invalidate a policy.