BMW B58 Gen1 Auxiliary Split Fuel System
The Spool Performance BMW B58 Gen 1 Auxiliary Fuel System is designed for B58 owners pushing beyond the limits of the factory fuel system who want a solution that’s properly engineered, easy to install, and built for long-term reliability.
From the beginning, our focus was on correct fuel architecture and real-world usability. Every component and layout choice was made to deliver stable, predictable fueling as power levels increase, while keeping installation clean and OEM-friendly.
As power levels rise on the B58 platform, fueling challenges most commonly come from supplying direct injection (DI) and port injection (PI) from the same fuel feed.
When DI and PI share a feed:
The pulsed nature of DI can introduce pressure fluctuations that disrupt fuel flow to the PI injectors
Port injection requires boost-referenced fuel pressure to maintain a consistent injector differential under load
At higher boost and airflow, maintaining precise and repeatable fueling becomes more difficult
By separating the DI and PI supply, each system operates independently and exactly as intended. The result is smoother fuel delivery, improved consistency, and greater confidence as power increases.
A significant amount of development time went into making this system straightforward to install without unnecessary modifications.
The OEM fuel pump top hat is retained using additional precision-machined aluminum fuel fittings that integrate directly into the factory top hat, eliminating the need for repinning or modifying factory wiring
Optional billet top hats are available separately for those who prefer them
A plug-and-play wiring harness is supplied for direct compatibility with the Reflex controller, simplifying installation and control
These design choices keep the install clean, reduce complexity, and maintain a factory-like fit and finish.
The system is built to grow with your setup:
Dual Walbro 450 fuel pumps included standard
Optional Walbro 525 upgrades available for higher horsepower goals
Choice of:
Standard relay configuration
Solid-state relay option for full PWM pump control
This flexibility allows you to match the fuel system to your current build while leaving room to expand.
All fuel lines included in the kit feature triple-layer PTFE construction:
Inner PTFE core for full fuel and ethanol compatibility
Middle stainless steel reinforcement for pressure strength
Outer nylon protective layer for abrasion resistance and durability
This ensures long-term reliability in high-heat, high-vibration environments and with aggressive fuel blends.
The system includes Spool Performance’s in-house designed compact fuel pressure regulator, developed specifically for auxiliary fuel applications:
Boost-referenced for accurate pressure control under load
Stable regulation at high flow rates
Compact design for clean engine bay packaging
Built to withstand demanding conditions
Whether you’re building a strong street car or planning a higher-power setup, the Spool Performance BMW B58 Gen 1 Auxiliary Fuel System delivers the fueling control and capacity needed to push the platform with confidence.
With properly separated DI and PI supply, OEM-friendly integration using precision aluminum fittings, Reflex compatibility, high-quality plumbing, and scalable pump options, this system is designed to perform reliably as your build evolves.
If you’re ready to upgrade your B58 fueling with a system that’s thoughtfully engineered and genuinely easy to live with, this is the solution built to get you there.
Fits all BMW vehicles equipped with the B58B30 engine (Gen 1), including but not limited to:
BMW 340i / 340i xDrive (F30 / F31 / F34) – 2016–2018
BMW 440i / 440i xDrive (F32 / F33 / F36) – 2016–2018
Note: Designed specifically for B58 Gen 1 (B58B30) platforms. Not compatible with B58 Gen 2 / B58TU systems unless otherwise specified.
-28%
$1,299.00
$1,799.00
-28%
$1,299.00
$1,799.00
-28%
$1,299.00
$1,799.00
$132.00