Adaptive ethanol tuning with guided setup, base octane calibration, optional map packs, and performance support add-ons.
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2021–2025 M240i · 2021–2024 M340i · 2021–2024 M440i · 2021–2025 Z4 M40i · 2021–2022 X3 M40i · 2021–2023 X4 M40i
Select the ecosystem you will use to flash and run the CarBahn calibration. Need Help Deciding? Chat with us live or contact us at (866) 558-4314 xt 1 to talk with our high performance sales team.
Leave selected if you need it. Remove anything you already own.
The base calibration includes flex fuel adaptation. Choose the octane level that matches your typical fuel.
Your selected base octane map includes CarBahn Flex Fuel calibration. Add custom calibration if you want this base map tailored to your vehicle, hardware, and power goals.
Your tune can hold four maps: your base tune and up to 3 additional maps for $200 each. Eligible maps can be custom tuned for additional power and build-specific calibration for an additional $200 each.
Smooth and refined calibration focused on everyday drivability with predictable throttle response and OEM-like behavior.
Reduced low-end torque for smoother street drivability and improved traction on imperfect road surfaces.
Street-focused rear-wheel-drive calibration with smoother torque onset and confidence on imperfect surfaces.
Progressive torque delivery designed to improve traction, balance, and confidence during track driving.
Built for extended lapping sessions with controlled torque delivery and repeatable thermal consistency.
Maximum engine response and aggressive torque targeting for competitive acceleration performance.
Rear-wheel-drive focused torque progression for predictable throttle modulation and improved traction control.
Reduced power and speed-limited calibration designed to protect the vehicle when driven by others.
Near-stock drivability intended for dealership visits, inspections, and service appointments.
Off-the-shelf 91 octane calibration for travel or regions where 91 octane is available.
Off-the-shelf 92 octane calibration for regions where 92 octane premium fuel is available.
Off-the-shelf 93 octane calibration for daily driving or travel where 93 octane is available.
Off-the-shelf 94 octane calibration for regions where 94 octane fuel is commonly available.
Off-the-shelf 95 octane calibration for international markets and higher-octane fuel availability.
High-octane calibration designed for race fuel or 100 octane pump gas applications.
Recommended supporting hardware and software for higher performance builds.
Please review and acknowledge the following before submitting your build.
93 octane + E40 · OEM stock versus CarBahn tuned
| Measurement | OEM stock | Tuned |
|---|---|---|
| Calculated flywheel power | 415 HP · 473 lb-ft | 611 HP · 640 lb-ft |
| Measured wheel power | 340 HP · 388 lb-ft | 501 HP · 525 lb-ft |
CarBahn Flex Fuel tuning continuously adapts ignition, fueling, and boost targets based on ethanol content in real time. Whether running premium pump fuel or blending up to E40, the calibration dynamically adjusts to optimize performance while maintaining drivability and refinement.
OEM stock versus CarBahn tuned on 93 octane + E40. Results vary with fuel quality, hardware, conditions, and vehicle configuration.
Gen 2 B58 · OEM stock versus tuned
415 HP
473 lb-ft torque
611 HP
640 lb-ft torque
340 HP
388 lb-ft torque
501 HP
525 lb-ft torque
No. This flex fuel tune is not covered by the CarBahn Factory Matching Warranty or Protection Plan. Review the full tuning acknowledgement in the builder before purchasing.
CarBahn Flex Fuel calibrations dynamically adapt between standard premium fuel and ethanol blends up to approximately E40 with the appropriate supporting hardware.
Yes. Maintaining OEM-like drivability, cold start behavior, and refinement are major priorities during calibration development.
Supporting hardware depends on the vehicle and intended use. The available Gen 2 B58 options include a high flow air filter and a heat exchanger for compatible G2x M240i, M340i, and M440i models.
Flex Fuel tuning can deliver substantial power gains, but reliability depends on choosing the correct map, monitoring ethanol content, staying within recommended torque limits, and using the supporting hardware required for your power level.
For long-term durability, CarBahn does not recommend sustained use above 40% ethanol content on OEM fuel systems. For very high-power use, a blend of approximately 60% 100-octane race gas and 40% E85 is preferred over full E85.
Once power targets increase, the engine, transmission, transfer case, cooling system, and fuel system all become part of the reliability equation.
| Engine Level | Max Recommended Torque | Recommended Hardware |
|---|---|---|
| OEM | 625 lb-ft | Transmission software, CarBahn heat exchanger |
| OEM+ / Street Stage 1 | 700 lb-ft | Transmission software, CarBahn heat exchanger |
| Street Stage 2 | 800 lb-ft | Transmission software, heat exchanger, transmission cooler, engine oil cooler, supplementary radiator |
| Street Stage 3 | 800 lb-ft | Transmission software, heat exchanger, transmission cooler, engine oil cooler, supplementary radiator |
| Race Stage 1 | 1,000 lb-ft | Transmission software, heat exchanger, transmission cooler, high-performance transmission, transfer case, engine oil cooler, supplementary radiator |
| Race Stage 2 | 1,000 lb-ft | Transmission software, heat exchanger, transmission cooler, high-performance transmission, transfer case, engine oil cooler, supplementary radiator |
| Race Stage 3 | 1,000 lb-ft | Transmission software, heat exchanger, transmission cooler, high-performance transmission, transfer case, engine oil cooler, supplementary radiator |
OEM: 525 lb-ft
OEM+: 600 lb-ft
Street Stage 2: 750 lb-ft
Race Stage 1/2: 1,000 lb-ft
OEM: 700 lb-ft
Street Stage 2: 800 lb-ft
Race Stage 2: 900 lb-ft
OEM: 700 lb-ft
Street Stage 2: 800 lb-ft
Race Stage 2: 1,000 lb-ft
OEM: 850 lb-ft
OEM+: 950 lb-ft
Street Stage 2: 1,050 lb-ft
Race Stage 2: 1,150 lb-ft
