Cobb LF Bypass Valve – Subaru WRX 2015-2021 / Forester XT 2014-2018 COBB

EMISSIONS

DESCRIPTION

The COBB LF BPV is a compact and lightweight by-pass valve that is capable of holding very high boost pressure without leaking. Its updated design reduces control volume by 30% allowing for extremely fast venting of boost when actuated. Innovative engineering and precision manufacturing result in a compact package able to fit in the confines of a tight engine bay. Due to the low weight of the components, the moving parts in the LF BPV have less inertia and can respond faster than heavier components in other bypass valves. This updated design uses a Banjo-fitting vacuum port which provides 360 degree adjustability of hose routing. This results in a simpler install and less potential leak points than the NPT ports. This new design also includes a piston o-ring seal that is twice the diameter of the old design allowing more seal compression and reduced wear. Adjustability of the spring seat is no longer needed due to the updated spring and seal design which provides a 60% increase in clamping force at peak boost while maintaining similar operation at idle and transient loads.

Note: This is an updated version of the original 745665 LF BPV that now includes a different internal spring.

Original Spring (uncoated)
Free length: 3.5″
Rate: 7.4 lbf/in
Bench cracking vacuum installed in LF BPV: -5.7 psi

New Spring (yellow)
Free length: 2.25″
Rate: 40.5 lbf/in
Bench cracking vacuum installed in LF BPV: -6.7 psi

WHY?

A compact and very lightweight bypass valve that is loaded with features and reliability holds high levels of boost without leaks.