Turbocharger Blow Off Valve

What Is a Turbocharger Blow Off Valve?

A turbocharger blow off valve (BOV) — also called a pressure relief valve or diverter valve — is one of the most important components in any forced-induction system. When you lift off the throttle at high boost, pressure builds rapidly between the turbocharger's compressor outlet and the closed throttle body. Without a way to release that pressure, the compressed air has nowhere to go and slams back into the compressor wheel — a damaging condition known as compressor surge. A blow off valve opens under these conditions, venting that excess pressure either back into the intake tract (recirculation) or out to the atmosphere, protecting the turbocharger and preserving its longevity.

Why a Quality BOV Matters

Not all blow off valves are created equal. A boost leak from a factory diverter valve can cause the ECU to drive the turbo harder to compensate for the loss, resulting in higher turbo RPM, more exhaust backpressure, and hotter compressor outlet temperatures — meaning the turbo is more stressed and the engine makes less power. Upgrading to a high-quality aftermarket BOV addresses these issues directly, improving sealing, throttle response, and overall reliability under high-boost conditions. Beyond performance, a well-chosen BOV delivers that iconic "whoosh" or atmospheric dump sound that turbo enthusiasts love — all without sacrificing drivability.

Types of Blow Off Valves

• Recirculating (Plumb-Back) BOV: Vents compressed air back into the intake system before the turbo inlet. Keeps the system quiet and avoids fueling issues on MAF-based engines.
• Atmospheric (Vent-to-Atmosphere) BOV: Vents pressure directly to the atmosphere for the classic "pssh" sound. Best suited for speed-density or properly tuned MAF setups.
• Dual-Port BOV: Combines both outlets in one valve, allowing adjustment between full recirculation and full atmosphere venting — or anything in between. GFB's venting bias adjustment system, for example, allows the driver to precisely control how much air vents from each of the two outlets — from 100% recirculation for silent factory operation to 100% atmosphere for maximum noise.

Key Considerations When Shopping

When choosing a blow off valve, consider your engine management system (MAF vs. speed-density), your boost targets, and whether you want sound. Factory-location bolt-on kits are the easiest to install, while universal valves offer more flexibility but may require custom plumbing. Spring rate and adjustability are also important — especially at elevated boost levels where a valve that opens too early or too late can hurt performance.

Top Blow Off Valve Brands

GFB – Go Fast Bits is the category leader, and for good reason. GFB pioneered the two-way blow off valve back in 1999 — a design that has since been copied by many other manufacturers — and in 2001 patented an adjustable blow off system that allows the blow off pressure to be continuously varied through one of two outlets. All GFB blow off and diverter valves are equipped with Turbo Management System (TMS) technology, which regulates air flow through the valve to help maintain boost pressure when the throttle is closed during a downshift, keeping the turbo spinning and reducing turbo lag.

Turbosmart is an Australian performance brand with decades of experience in turbo technology, offering a comprehensive lineup of BOVs ranging from entry-level replacements to race-proven valve configurations. Their products are a favorite among Subaru, Mitsubishi, and Nissan enthusiasts for their robust construction and broad fitment coverage.

HKS brings Japanese engineering precision to the BOV market. Known for their Super Sequential Blow Off Valve (SSQV) series, HKS valves are iconic in the tuner community for their distinctive sound signature and high-quality billet aluminum construction, with a long history of use in motorsport applications.

Torque Solution focuses on direct-fit, OEM-style replacement BOVs that are engineered to address the known weaknesses of factory diverter valves. Their offerings are particularly popular as a straightforward, no-tune-required upgrade for turbocharged enthusiasts who want better reliability without complicated installation.