Tuning · BMW M340i (G20 / G21)
M340i
B58 Gen 2
The Gen 2 B58 in saloon and Touring form. Hand-calibrated from Stage 1 to a fully bespoke big-turbo build. Choose your package, send your build to Samuel, and get a tune that fits the way you actually drive.
Engine
B58 Gen 2
Stock
374 bhp · 500 Nm
Stage 3 ceiling
374 bhp
About this tune
The G20 / G21 M340i (2019-present) is the M-Performance variant of the 3 Series with the B58 Gen 2, the revised, smoother, more efficient version of BMW's single-turbo straight-six. Stock is 374 bhp / 500 Nm, sent through the ZF 8HP with xDrive standard in most markets. Available as the G20 saloon and G21 Touring; both share the identical drivetrain and respond to the same Stage 1 / Stage 2 map. The M340i is one of the most popular B58 Gen 2 chassis worldwide and the closest thing to an M3 you can buy without paying M-car money.
BMW M340i tuning
For most owners the M340i is the sensible M3 alternative: a G20 saloon or G21 Touring that does school runs and motorways all week, with an M-lite badge rather than a full M budget. Tuning is what closes the gap. The chassis, brakes and cooling were engineered with far more in reserve than the factory calibration uses, so a remap is the single most cost-effective change you can make to the car.
Both bodies leave the factory at 374 bhp and 500 Nm. Samuel's Stage 1 file raises that to 440 bhp and 680 Nm on completely standard hardware, and because the saloon and Touring share an identical drivetrain the calibration carries across both without compromise. Stage 2, with a downpipe and intake fitted, targets 480 bhp and 700 Nm, enough to put a family 3 Series firmly into genuine M-car territory.
Owners chasing more can keep going: hybrid and big-turbo conversions stretch the platform to around 1,000 bhp with proper fuelling behind them. The process is entirely remote. Samuel hand-builds the map for your exact car and fuel, loads it to your flashing platform of choice, bootmod3, MHD or MG Flasher, inside 24 hours, and the stock file travels with it so reverting to factory takes one flash.
Configurator
Build your M340i tune
Choose your stage — Stage 1, Stage 2 or Stage 3 — add the options that fit your car, and send the full build to Samuel for a custom remote remap. He'll quote, schedule, and personally calibrate within 24 hours of confirmation.
Add a stage or add-on
£0
Engine guide
BMW M340i tuning, stages, hardware and what to expect from the G20 B58 Gen 2
The M340i runs the B58 Gen 2, BMW's revised 3.0-litre single-turbocharged inline-six fitted to the G20 saloon, G21 Touring, M440i, M240i G42, Z4 M40i, X3 / X4 M40i and the Toyota Supra 3.0. From the factory, BMW set the M340i at 374 bhp / 500 Nm; the hardware ceiling sits considerably higher. BMW M340i tuning with Samuel targets that headroom with a calibration matched to the G20 / G21 chassis behaviour and 8HP gearbox. BMW M340i G20 tuning and BMW M340i G21 tuning use the same map; only the Touring exhaust geometry differs slightly further back.
Stage 1
440 bhp · 680 Nm
No hardware required. The MG1CS003 DME is flashed via the OBD port, boost, ignition timing, fuel delivery and torque limiters all revised. BMW M340i Stage 1 unlocks 440 bhp and 680 Nm from the OEM hardware (up from 374 / 500 stock). The BMW M340i chip tuning starting point and by far the most popular single modification on the G20 / G21 platform, the most cost-effective change you can make.
Every M340i tune Samuel produces is calibrated individually for the specific car, fuel grade and installed hardware, not a base map loaded and left. BMW M340i tuning done correctly accounts for the G20 chassis behaviour, the 8HP gearbox calibration and UK fuel quality; the map is reviewed against your data logs after the first flash and revised before sign-off.
Compatibility
Platform and hardware compatibility
Bootmod3 (BM3)
Full B58 Gen 2 support on the MG1CS003 DME across every Gen 2 chassis (M340i, M440i, M240i G42, Z4 M40i, X3/X4 M40i, Supra 3.0). OBD-port flashing, realtime monitoring via the BM3 app. The most widely used platform for B58 Gen 2 tuning.
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MHD
Full B58 Gen 2 support. Suitable for Stage 1 and Stage 2. Strong data-logging toolset and active community support.
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MG Flasher
Full B58 Gen 2 support. Clean interface and reliable flash process. A common alternative to BM3 for owners who prefer the MG ecosystem.
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xHP Flashtool
Compatible with the ZF 8HP gearbox fitted to every B58 Gen 2 chassis. Gearbox calibration matched to the ECU map, strongly recommended at Stage 2 and above where torque jumps significantly. Available as an add-on.
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ECU: MG1CS003 DME across all B58 Gen 2 production. Accessible via OBD for Stage 1 and Stage 2; bench-flash only required for some Stage 3 hybrid setups.
M340i specs & stage targets
BMW M340i tuning at a glance
- Engine
- B58 Gen 2
- Body styles
- G20 Saloon · G21 Touring
- Chassis codes
- G20 / G21
- Production
- 2019–present
- Drivetrain
- xDrive (RWD in some markets)
- Gearbox
- 8-speed ZF automatic
- Stock output
- 374 bhp · 500 Nm
- Tuning ceiling
- ~1000 bhp on the right hardware
| Stage | Target |
|---|---|
| Stage 1 | 440 bhp · 680 Nm |
| Stage 2 | 480 bhp · 700 Nm |
| Stage 3, Hybrid Turbo | 550-1000 bhp depending on spec |
| Stage 3, Big Turbo Kit | 550-1000 bhp depending on spec |
FAQ
M340i tuning — frequently asked questions
Stage 1 takes the M340i from its factory 374 bhp and 500 Nm to 440 bhp and 680 Nm with no parts required. Adding a downpipe and intake for Stage 2 raises the target to 480 bhp and 700 Nm on the original turbo. Both maps are calibrated individually for your car and fuel grade rather than pulled from a generic file.
Yes. The G21 Touring carries exactly the same B58 Gen 2, ZF eight-speed and ECU as the G20 saloon, so the stages, targets and prices are identical. If anything the estate is the sweet spot: the extra practicality changes nothing about how the drivetrain takes the map, and a 480 bhp Touring remains one of the great all-purpose fast cars.
It can. If BMW ties a specific failure to the tune, the related claim may be refused, and dealers can detect flash history. Samuel calibrates against the B58's mechanical limits rather than chasing peak numbers, and the map reverts fully to the supplied stock file, so many owners flash back before scheduled dealer work. Treat warranty risk as real but manageable.
Stage 1 and Stage 2 files are built around the fuel you tell Samuel you use, which in the UK usually means 99 RON super unleaded, letting the calibration hold its targets consistently. The map is written for a stated grade, so stick with it to get the performance you paid for.
You send your build details: model year, gearbox, hardware and fuel. Samuel calibrates the file by hand, it lands in your bootmod3, MHD or MG Flasher account within 24 hours, and you flash it through the OBD port in around fifteen minutes. Datalogs afterwards let Samuel fine-tune the map to your individual car.
Keep exploring
Keep exploring M340i tuning
Other B58 Gen 2 models we tune: M240i, M440i, Z4 M40i, X3 M40i, X4 M40i, Supra 3.0.
Engine guide
B58 Gen 2 tuning
Every B58 Gen 2 BMW we calibrate, with the full Stage 1, 2 and 3 breakdown for the engine.
Learn moreStages
Stage 1 & Stage 2 explained
What separates Stage 1 from Stage 2 on the M340i, the real-world gains and the hardware each one needs.
Learn morePricing
How tuning is priced
How the licence, off-the-shelf maps and custom calibration are priced. We quote your exact spec, never a fixed menu.
Learn moreGuide
What is bootmod3?
New to remote flashing? A plain-English explainer on the platform and how a custom map reaches your car.
Learn more