08/17/2026
Spool Performance BMW Auxiliary Fuel System
When adding port injection to a high-power BMW, the low-pressure fuel system needs to be designed correctly. Running the factory direct injection and port injection systems from the same fuel supply can create pressure fluctuations and fuel starvation as demand increases.
Most upgraded low-pressure systems operate at static pressure. As boost rises, the effective pressure differential across the port injectors decreases, forcing the calibration to rely heavily on injector compensation tables. The higher the boost, the larger the potential error becomes.
The Spool Auxiliary Fuel System gives the port injection system its own dedicated feed, return and boost-referenced regulator. Fuel pressure rises 1 psi for every 1 psi of boost, maintaining consistent pressure differential across the port injectors. This provides more predictable injector flow and accurate fuel delivery under load.
Separating the DI and PI fuel supplies is especially important at higher power levels. When both systems compete for the same fuel source, pressure instability can affect the factory high-pressure system and contribute to damaged DI injectors. Our system allows the factory direct injection system and supplemental port injection system to operate independently.
What’s Included
* 2 genuine Walbro fuel pumps
* 2 genuine Walbro fuel filters
* Spool platform-specific dual-pump bracket
* Spool high-flow 10-micron stainless-steel fuel filter assembly
* Dedicated PTFE crimped feed and return lines from the fuel tank to the fuel rail and regulator
* 2 ground-activation wiring harnesses for pump control
* Genuine low-profile Radium DMR boost-referenced fuel-pressure regulator
* Injection-molded plastic fuel-pump top hat manufactured to the same design as the OEM unit for simple plug-and-play installation and proper sealing
The Spool Auxiliary Fuel System is a complete, cost-effective fueling solution built with genuine components from brands you already know and trust. No questionable pumps, generic regulators or leak-prone aftermarket top hats—just proven parts, proper fuel-system architecture and everything required for a clean installation.
