BMW G42 M240i — The Complete Upgrade Guide

The BMW G42 M240i is one of the most underrated performance cars in the current BMW lineup. In a range dominated by conversation about the M2, M3, and M4, the M240i quietly delivers one of the most complete everyday performance car experiences available — a 374bhp B58 straight-six, xDrive all-wheel drive, a compact two-door coupe body, and a level of daily usability that the harder-edged M cars above it cannot match.

The M240i's relationship to the G82 M4 is similar to the M340i's relationship to the G80 M3 — it shares the same basic platform, the same basic body architecture, and a version of the same straight-six engine family in a less extreme state of tune. And like the M340i, it responds to the right upgrades with a transformation that brings it significantly closer to the M car above it in performance and visual character at a fraction of the total cost.

This guide covers the complete upgrade path for the BMW G42 M240i — every modification category in the right order, with the detail needed to make informed decisions at each stage.

Understanding the G42 M240i as a Platform

The G42 M240i sits on BMW's CLAR platform — shared with the G80 M3, G82 M4, G20 3 Series, and G22 4 Series. This platform sharing has direct implications for the M240i's upgrade path — coilover manufacturers, exhaust developers, and aero part producers who have developed products for other CLAR platform cars have a deep understanding of the architecture the G42 shares.

The B58 engine in the M240i is a detuned version of the same basic engine family used across the G-series BMW range. In M240i specification it produces 374bhp and 500Nm — significantly less than the S58 in the M2, M3, and M4, but a figure that places it comfortably ahead of most of its direct competition. The B58 is one of the most thoroughly validated tuning platforms in the current performance car market — its response to exhaust, intake, and ECU modification is well-documented and the power gains available are meaningful.

The M240i's xDrive all-wheel drive system is standard across all markets — unlike the M2 which is rear-wheel drive only, the M240i's all-wheel drive creates a different dynamic character that suits everyday performance driving and adverse weather conditions particularly well.

Carbon Fiber Front Splitter

The G42 M240i's front end is one of its strongest visual angles — the M Sport bumper's wide lower section, the prominent front intakes, and the car's compact two-door proportions create a front profile that looks appropriately sporty without the overt aggression of the full M cars. A carbon fiber front splitter extends this character further, adding visual mass to the lower bumper and giving the M240i a more planted, performance-oriented front end appearance.

The G42 M240i's M Sport front bumper is specific to this model — it differs from the G22 4 Series M Sport bumper in its lower section geometry, which means splitter options must be verified for G42-specific fitment rather than assumed to be compatible with the broader 2 Series or 4 Series range. Always confirm chassis code specific fitment when ordering front splitter components for the M240i.

For M240i owners building toward a more M2-inspired visual direction, a more aggressive front splitter with integrated canards creates a front end treatment that references the M2's harder-edged aero philosophy while remaining appropriate for a car that sees daily use.

Exhaust Upgrades — The B58 Deserves to Be Heard

The B58 in the G42 M240i is acoustically impressive for a road car but significantly restricted by the factory exhaust's noise regulation compromises. A quality valved cat-back exhaust system is the most impactful single upgrade available for the M240i's character — transforming the straight-six's sound from refined and muted to something considerably more involving.

In closed mode a quality valved system remains completely civilised — appropriate for early morning departures from residential areas and urban driving where noise is a consideration. In open mode the B58 reveals a linear, sophisticated straight-six character that builds progressively from a deep idle note to an intense top-end roar that is genuinely impressive and entirely disproportionate to the M240i's relatively modest market positioning.

High-flow sports cat downpipes for the B58 in the G42 deliver meaningful performance gains when combined with a supporting ECU remap. The B58's response to downpipes and a quality tune is well-documented across multiple G-series platforms — power gains of 80–100bhp over standard are achievable on a comprehensive tune, transforming the M240i from a refined everyday performance car into something that genuinely challenges cars positioned significantly above it in the market.

The combination of a fully tuned B58 M240i — downpipes, intake, and a quality remap — with a comprehensive carbon aero package creates a car that competes with or exceeds the previous generation M2 in both visual presence and driving performance. This is the most compelling case for the G42 M240i as a build platform — the total investment required to reach this level is dramatically lower than the equivalent M2 purchase price.

Suspension Upgrades

The G42 M240i's factory suspension is well-sorted for a compact everyday performance car — its adaptive dampers provide a reasonable spread between comfort and sport settings, and the M Sport suspension tuning gives it a more purposeful baseline than the standard 2 Series variants.

A quality coilover kit dropping the M240i 15–20mm transforms the compact coupe's visual stance dramatically. The G42's proportions — shorter than the G22 4 Series and significantly shorter than the G80 M3 — mean that the arch gap reduction from lowering is proportionally very visible. A correctly set up G42 on quality coilovers sits exactly as a compact performance coupe should — close to the arches, level, and purposeful from every angle.

The G42's adaptive damper system requires coilover kits that specifically account for the electronic integration — always verify adaptive damper compatibility when ordering suspension upgrades for the M240i. Kits that don't address this create warning lights and system faults after installation that are irritating and potentially expensive to resolve.

Geometry setup after coilover installation is essential — additional front negative camber on the G42 transforms the car's turn-in response and cornering grip in a way that is immediately apparent from the driver's seat. The compact body means geometry changes have a direct and responsive effect on the car's dynamic character — a properly set-up G42 on quality coilovers with correct geometry is one of the most rewarding everyday performance cars available at any price point.

Carbon Fiber Side Skirts and Rear Aero

The G42 M240i's compact coupe body creates a tight, well-proportioned canvas for carbon fiber side skirt extensions and rear aero additions. Carbon side skirts following the factory M Sport sill line add visual depth to the M240i's flanks and connect the front and rear aero elements cohesively — creating a complete lower body package that transforms the car's profile from compact sports coupe to something with a much more purposeful, performance-oriented character.

A carbon fiber rear diffuser completes the lower body package. The M240i's twin exhaust arrangement creates a visual focal point for diffuser designs, and a carbon replacement adds depth and race-derived detailing to the rear bumper that better reflects the car's modified performance specification. Combined with a quality exhaust tip upgrade or a full aftermarket exhaust system, the G42's rear end can be transformed from understated to properly aggressive.

A carbon fiber boot lid spoiler sits naturally on the G42's short coupe boot section. The compact body means a spoiler has a proportionally large visual impact on the M240i — a well-chosen lip spoiler or blade spoiler completes the rear visual package and gives the car a finished, cohesive appearance that the unmodified boot lid cannot achieve alongside aggressive front and side aero.

Wheel Upgrades

The G42 M240i uses the 5x112 bolt pattern shared across modern BMW's lineup — giving access to the same enormous range of compatible aftermarket wheel options as the G20, G22, G80, and G82. For M240i builds targeting a more M2-inspired appearance, M2-specification wheel sizes in appropriate offsets create a stance that references the more aggressive M car directly.

The G42's compact body means wheel choice has a proportionally large visual impact — on a shorter car the wheel-to-body ratio is higher, making the wheel selection one of the most visually significant decisions in the build. A wheel that is slightly too small looks immediately wrong on the G42's compact body. A wheel that fills the arch correctly — close to the fender lip with appropriate offset — looks aggressive and purposeful in a way that suits the car's compact proportions perfectly.

Carbon Fiber Mirror Caps and Detail Upgrades

Carbon fiber mirror caps are among the most immediately impactful detail upgrades available for the G42 M240i and one of the most accessible entry points into the car's upgrade path. The M240i's compact body makes the mirror caps proportionally prominent — the upgrade is correspondingly visible and impactful, particularly on lighter body colours where the carbon contrast is striking.

Carbon fiber interior trim — dashboard inserts, centre console panels, door card accents, and gear selector surrounds — brings the G42's cabin visual language closer to the M2's more extensively trimmed interior. For M240i owners who spend significant time in the car, interior carbon upgrades transform the daily driving environment and create a more engaging, performance-oriented cabin character that the standard interior's more conservative trim cannot match.

The M240i vs M2 — The Build That Makes the Argument

The G42 M240i's most compelling case as a build platform is the comparison to the G87 M2. Both cars share the same basic body architecture and CLAR platform. The M2 has the S58 engine, rear-wheel drive, and a harder-edged suspension setup. The M240i has the B58, xDrive, and a more everyday-focused character.

A fully built M240i — tuned B58 with downpipes delivering 450–470bhp, quality coilovers with correct geometry, comprehensive carbon aero package, and appropriate wheels — creates a car whose performance and visual presence genuinely challenges the M2 at a total project cost that is significantly lower than an equivalent M2 build. The M240i's xDrive provides better all-weather capability than the M2's rear-wheel drive, and its B58 engine's tuning headroom — while less than the S58's — is more than sufficient for a genuinely fast everyday car.

For buyers who want to maximise the performance and visual result relative to the total investment, the G42 M240i build path is one of the most compelling value propositions in the current performance car market.

At Velocity Car Parts all BMW G42 M240i parts are verified for G42-specific fitment and backed by our fitment guarantee. Browse the full BMW G42 collection and build your M240i the right way.