BMW B58 Gen2 Auxiliary Split Fuel System

BMW B58 Gen2 Auxiliary Split Fuel System

The Spool B58 Gen 2 auxiliary fuel system is intended for builds that have moved beyond the capacity of the factory system. Its key design feature is separating the direct-injection (DI) and port-injection (PI) fuel supplies instead of feeding both from one line.

The split layout isolates the PI rail from DI pressure pulsations and allows boost-referenced fuel pressure to maintain a consistent injector differential under load. The result is more stable, predictable fuel delivery at higher power levels.

System highlights

• Separate DI and PI feeds
• Dual Walbro 450 pumps in the standard configuration
• Plug-and-play Reflex-compatible harness
• Triple-layer PTFE lines with stainless reinforcement and nylon protection
• Compact boost-referenced Spool fuel-pressure regulator
• Factory pump top retained with model-specific billet fittings

Pump control, pressure regulation, injectors and calibration must be designed as one system. Higher-flow pump and PWM-control options are also available; check the product selections.

Example vehicle fitment

• BMW M340i / BMW M340i xDrive – 2020–
• BMW M440i / BMW M440i xDrive – 2021–
• BMW X3 M40i – 2020–
• BMW X4 M40i – 2020–

Always confirm the engine, chassis, model year and part-specific fitment before ordering. Not every version within a model range necessarily uses the same part.