The BMW G01 X3 M40i and G02 X4 M40i sit in a brilliant sweet spot – practical, refined, and powered by BMW’s hugely capable B58 engine. From the factory, they already deliver strong performance, but the real appeal lies in just how much additional power and character can be unlocked with the right upgrades.
At R44 Performance, we’ve tuned, supplied parts for, and worked on countless G-Series B58 cars over the years, so this guide is designed to give you a clear, honest overview of the tuning stages available, what’s involved at each step, and what sort of results you can realistically expect.
Stage 1 – Software-Only Performance Gains
Stage 1 tuning is the simplest and most accessible way to extract extra performance from your G01 X3 or G02 X4 M40i. This stage focuses entirely on software, with no hardware changes required.
Most owners choose either:
- An ECU remap via platforms such as MHD, or
- A custom calibration from a professional tuning company
Both approaches optimise boost pressure, ignition timing, and fuelling to safely unlock additional power and torque from the stock B58 setup.
If you’re looking for an alternative to a traditional remap, a piggyback system such as RaceChip is also a popular option. These modules can deliver gains of 75+ bhp, 77+ Nm of torque, and in some cases up to 15% better fuel economy, while remaining fully reversible.
Who Stage 1 is for:
Drivers wanting a noticeable increase in performance with minimal cost, zero hardware changes, and excellent day-to-day drivability.
Stage 2 – Hardware Upgrades for Serious Gains
Stage 2 builds on the software improvements of Stage 1 by adding key bolt-on hardware that allows the B58 engine to breathe more efficiently and run higher power levels safely.
Our Recommended Stage 2 Hardware
At R44 Performance, we consistently recommend the following combination for outstanding value and results:
- K&N high-flow panel filter
- DCE 5.2 inch catless downpipe with heat shield
- DCE resonator / OPF delete midpipe
Together, these upgrades significantly reduce exhaust back pressure, improve airflow, and allow your tuner to safely extract more power from the B58.
Full exhaust systems are also available if you're looking for both maximum sound & maximum weight saving. A popular option is this cat-back system from Valvetronic Designs. However, a midpipe is the best-value option to achieve the power gains you're after.
With the correct Stage 2 calibration, this setup will comfortably achieve over 500 bhp at the crank, transforming how the car accelerates while retaining everyday usability.
Optional Intake Upgrades – Worth It?
A full intake system isn’t strictly necessary for strong Stage 2 power figures, but some owners choose one for sound and visual impact.
- Eventuri carbon intake system: Visually stunning, beautifully engineered, and produces an addictive intake sound. It is, however, a premium option and not essential for excellent power gains.
- MST intake system: A much more affordable alternative, offering great sound and solid performance benefits. It’s important to note that this option is pre-LCI only, so facelift models are not compatible.
R44 Performance Stage 2 Kit
We also offer a Stage 2 hardware kit that bundles the three core upgrades:
- K&N high-flow panel filter
- DCE 5.2 inch catless downpipe with heat shield
- DCE resonator / OPF delete midpipe
This package is designed as a cost-effective, proven solution for customers who want a straightforward route to Stage 2 power levels without mixing and matching parts. Shop now
Stage 3 – Turbo Upgrades & Big Power
Stage 3 is where things start to get very serious. At this level, the factory turbocharger becomes the limiting factor. While the stock unit is excellent, it simply can’t safely sustain much beyond the 500 bhp mark.
Turbo Upgrade Recommendation
Our go-to solution is the Pure Turbos PURE 800 turbocharger.
We’ve supplied and installed these on a wide range of G-Series B58 vehicles for many years, and the results speak for themselves.
Key benefits include:
- Fast spool characteristics
- Exceptional build quality
- Proven reliability at high power levels
With the PURE 800 fitted:
- Up to 700 horsepower at the wheels is achievable on suitable fuels & with forged engine components
- On pump fuel, most setups sit comfortably around 550 horsepower at the wheels
Cooling & Supporting Upgrades
At Stage 3, managing heat becomes critical.
- CSF B58 Gen2 front mount heat exchanger: This features a much larger core, increased cooling capacity, and an integrated rock guard for protection. Unlike the OEM unit, it’s constructed from aluminium rather than brittle plastic, greatly improving durability.
- Motul coolant: We typically recommend Motul over OEM coolant for improved thermal stability under higher load conditions.
Stage 3+ – Fuel System & Ethanol Power
The G-Series B58 uses the B58TU engine, which benefits from an upgraded high-pressure fuel pump from the factory. This gives it impressive headroom, but once you’re chasing even higher outputs, further upgrades are required.
Flex Fuel & Power Limits
Rather than immediately upgrading fuel pumps, we typically recommend:
- Adding flex fuel capability
- Running an ethanol blend
This approach allows you to safely achieve 600+ horsepower at the wheels. Beyond this point, engine reliability becomes a concern, and pushing further would require forged internal components and a fully built engine.
Reliability Upgrade – Charge Pipe
Regardless of tuning stage, one upgrade we always recommend is a metal charge pipe.
The OEM charge pipes are plastic and prone to splitting under increased boost. We see failures far too often.
Our preferred solution is the FTP Motorsport charge pipe – an affordable, well-made upgrade that significantly improves reliability and peace of mind.
Speak to R44 Performance
Every build is different, and the “right” setup depends on your goals, budget, and how you use your car. If you’d like tailored advice, help selecting parts, or to discuss workshop installation and tuning, our experienced sales team is always happy to help.
Get in touch with us to plan your BMW G01 X3 or G02 X4 M40i build properly – whether you’re starting with Stage 1 or aiming for serious Stage 3 power.
