BMW B58 Gen2 Auxiliary Split Fuel System
Spool Performance B58 Gen 2 Auxiliary Fuel System
The Spool Performance B58 Gen 2 Auxiliary Fuel System is designed for B58 Gen 2 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 start, our focus was on correct fuel architecture and real-world usability. Every component and layout choice was made to deliver stable, predictable fueling at higher power levels while keeping installation clean and OEM-friendly.
Why a Properly Designed DI + PI Fuel System Matters
As power levels increase on the B58 Gen 2 platform, fueling challenges typically arise when direct injection (DI) and port injection (PI) are supplied from the same fuel feed.
When DI and PI share a feed:
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The pulsed nature of DI can introduce pressure fluctuations that disrupt fuel flow to the PI injectors
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Port injection requires boost-referenced fuel pressure to maintain consistent injector differential under load
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At higher boost and airflow, maintaining precise and repeatable fueling becomes more difficult
By separating the DI and PI supply, each system is able to operate independently and exactly as intended. The result is smoother fuel delivery, improved consistency, and greater confidence as power increases.
Designed to Install Cleanly
A significant amount of development time went into making this system straightforward to install without unnecessary modifications.
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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
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Optional billet top hats are available separately for those who prefer them
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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.
Scalable Pump and Control Options
The system is built to grow with your setup:
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Dual Walbro 450 fuel pumps included standard
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Optional Walbro 525 upgrades available for higher horsepower goals
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Choice of:
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Standard relay configuration
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Solid-state relay option for full PWM pump control
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This flexibility allows you to match the fuel system to your current build while leaving room to expand.
High-Quality Fuel Plumbing
All fuel lines included in the kit feature triple-layer PTFE construction:
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Inner PTFE core for full fuel and ethanol compatibility
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Middle stainless steel reinforcement for pressure strength
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Outer nylon protective layer for abrasion resistance and durability
This ensures long-term reliability in high-heat, high-vibration environments.
Compact, Purpose-Built Fuel Pressure Regulation
The system includes Spool Performance’s in-house designed compact fuel pressure regulator, developed specifically for auxiliary fuel applications:
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Boost-referenced for accurate pressure control under load
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Stable regulation at high flow rates
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Compact design for clean engine bay packaging
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Built to withstand demanding conditions
Built to Support Serious B58 Gen 2 Builds
Whether you’re building a strong street car or planning a higher-power setup, the Spool Performance B58 Gen 2 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 Gen 2 fueling with a system that’s thoughtfully engineered and genuinely easy to live with, this is the solution built to get you there.
Fitment
This auxiliary fuel system is designed for BMW vehicles equipped with the B58 Gen 2 engine, including:
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BMW M340i / BMW M340i xDrive – 2020+
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BMW M440i / BMW M440i xDrive – 2021+
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BMW X3 M40i – 2020+
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BMW X4 M40i – 2020+
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BMW B58 Gen2 Auxiliary Split Fuel System
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FAQs
Please read our FAQs page to find out more.
Are OEM products more expensive than aftermarket alternatives?
OEM products might have a higher upfront cost compared to aftermarket parts, but their superior quality and durability often make them a more cost-effective choice over time. Investing in OEM ensures you’re getting parts specifically designed for your vehicle, which can lead to better performance and longevity.
Can I purchase OEM parts online or do I need to visit a dealership?
You don’t need to visit a dealership to get OEM parts. You can conveniently purchase genuine OEM components from authorized distributors and reputable online retailers like Turbo Tech Performance. Our online store provides a wide selection of high-quality parts delivered straight to your door.
Are parts from brands like Mopar, ACDelco, and Motorcraft interchangeable between different vehicle brands?
No, parts from Mopar, ACDelco, and Motorcraft are typically designed for specific vehicle brands. It’s crucial to ensure compatibility with your vehicle’s make and model by checking part numbers and consulting with a knowledgeable expert.
Can I install OEM parts myself, or is it better to have a professional handle it?
While some OEM parts can be installed by DIY enthusiasts, the complexity of installation can vary. For the best results and to ensure proper fitment and performance, we recommend having a trained mechanic install the parts, especially if you’re unfamiliar with automotive repairs.
Do OEM parts come with a warranty?
Yes, many OEM auto parts come with a manufacturer’s warranty that covers defects or issues. Be sure to check the warranty details for each part at the time of purchase, and keep your receipt for any potential warranty claims.