BMW B58 Gen 2 Spool Auxiliary Split Fuel System

The Spool B58 Gen 2 auxiliary fuel system gives your port injection its own fuel feed, separate from direct injection, for stable fueling as power climbs.

Why you need it

When DI and port injection share one feed, the pulsing of the DI pump can upset fuel delivery to the port injectors, and port injection needs boost-referenced pressure to stay consistent under load. Splitting the two supplies lets each run exactly as intended, so fueling stays smooth and repeatable at higher boost.

Fits

• BMW M240i (B58 Gen 2)
• BMW M340i (B58 Gen 2)
• BMW M440i (B58 Gen 2)
• BMW 540i (B58 Gen 2)
• BMW X3 M40i and X4 M40i (needs a different in-tank bracket)

Features

• Separate DI and port injection fuel supply
• Dual Walbro 450 pumps standard, Walbro 525 upgrade available
• Retains the OEM top hat using machined aluminum fittings, no repinning
• Plug-and-play harness for the Reflex controller
• Triple-layer PTFE, stainless and nylon fuel lines
• Radium Engineering boost-referenced fuel pressure regulator

Good to know

Choose Walbro 450 or Walbro 525 pumps, both with check valves, at checkout. The 525 suits higher power goals. A solid-state relay option for full PWM pump control is sold separately and needs two harnesses per kit. The system is designed around a Reflex controller and needs a supporting tune. X3 M40i and X4 M40i need a different in-tank bracket, so confirm before ordering. Professional installation is recommended.