340i (F30/F31/F34)

A remap gives the biggest change per pound on the B58, typically adding a substantial increase in mid-range torque on stock hardware. Owners commonly pair it with an upgraded heat exchanger to control intake temperatures, then add a sports-cat downpipe and intake for higher-stage software. On the chassis side, coilovers or lowering springs and uprated brake pads are the usual first upgrades. Keep spark plugs fresh, as tuned B58s are sensitive to worn plugs.

Yes. A sports-cat downpipe changes exhaust flow and boost behaviour, so it should be paired with a Stage 2 map written for it. Running a Stage 1 map with an upgraded downpipe can cause overboost, and the wrong combination often triggers fault codes. Choose a quality sports-cat design for a UK road car, as the car must still meet MOT emissions requirements. Your tuner's map notes will specify which hardware each stage expects.

The first-generation B58 in the 340i uses a plastic charge pipe. Failures are less common than on the N55, because the B58's intercooler sits in the intake manifold and the pipe moves with the engine, but it can crack at higher boost. Many owners fit an aluminium pipe as inexpensive insurance before Stage 2 tuning, and it is essential if you add methanol injection, as the factory pipe has no injection port.

The 340i uses the first-generation B58, which runs around 200 bar injection pressure, while the later B58TU in the G20 M340i uses 350 bar injection and other revisions. In practice, the earlier engine's high-pressure fuel pump limits ethanol blends sooner, so higher E-content maps on a 340i usually need a fuel pump upgrade. Engine-specific parts such as charge pipes, downpipes and heat exchangers are generally not interchangeable between the two generations.

Yes. Lowering springs work with BMW's adaptive (VDC) dampers, which only adjust damping electronically, and owners commonly keep the adaptive function after lowering. Coilovers replace the adaptive dampers, so a cancellation module is needed to prevent warning lights; KW provides specific kits for this. Springs and coilovers differ between Saloon, Touring and xDrive models, so check the fitment details on each R44 product or save your 340i to My Garage.

The eight-speed ZF automatic in the 340i is widely regarded as strong and handles typical Stage 1 and Stage 2 torque levels well when it is in good health. A gearbox service with fresh fluid is sensible on higher-mileage cars before tuning, and transmission software can improve shift speed and torque handling on bigger builds. If you are planning an upgraded turbo, discuss the gearbox and torque limits with your tuner as part of the plan.