BMW S58 Spool Auxiliary Split Fuel System

The Spool S58 auxiliary fuel system gives BMW M2, M3 and M4 owners a properly split DI and PI fuel supply for stable fueling past the limits of the factory system.

Why you need it

When direct injection and port injection share one feed, DI pulses disturb PI fuel flow and it gets harder to hold boost-referenced pressure at high load. Splitting the supply lets each system run as intended for smoother, more consistent fueling as power climbs. The OEM top hat is retained with machined aluminum fittings, so no repinning or factory wiring changes are needed.

Fits

• BMW M3 (G80, 2021+)
• BMW M3 Touring (G81, 2023+)
• BMW M4 (G82 / G83, 2021+)
• BMW M2 (G87, 2023+)

Features

• Separate DI and PI fuel supply
• Retains the OEM top hat with precision aluminum fittings
• Plug-and-play harness for the Reflex controller
• Dual Walbro 450 pumps, or Walbro 525 upgrade
• Triple-layer PTFE / stainless / nylon fuel lines
• Boost-referenced Radium Engineering fuel pressure regulator

Good to know

Choose dual Walbro 450 pumps, or Walbro 525 pumps for higher power goals; both come with check valves. A solid-state relay for full PWM pump control is sold separately, and the kit needs two activation harnesses. A tune with port injection control is required. Professional installation is recommended.