The Mach 2 Atmosphere Upgrade Kit allows a GFB Mach 2 valve to be converted from recirculating operation to atmosphere venting.

This kit includes a trumpet outlet, a firmer spring, and a 20mm hose plug.

To correctly vent the Mach 2 valve to atmosphere, the piston must remain fully closed at idle and the recirculation hose must be blocked. The 5920 Atmosphere Conversion Kit supplies a 20mm hose plug to seal the recirc hose, along with a trumpet that replaces the standard hose outlet on the Mach 2. While the trumpet is not required for correct operation, it increases the venting sound. The kit also includes the firmer spring (part #6115).

Mach 2 valves are supplied as standard with a softer spring (part #6116), which is suitable for recirculation setups or engines with an idle vacuum of 18 inHg or less. If the piston remains closed at idle with the existing spring installed, there is no need to replace it.

If the piston sits partially open at idle even with maximum spring pre-load applied, the firmer spring included in this kit should be installed. This helps prevent drivability issues such as stalling or backfiring when converting the valve to atmosphere venting.