This guide explores Blow Off Valves (BOVs) used in Subaru turbocharged cars. We'll clear up confusion around terminology and delve into the purpose, benefits, and drawbacks of aftermarket BOVs.

Understanding BOV Terminology

• BOV vs. BPV: "Blow Off Valve" (BOV) is a general term, but Subaru uses a Bypass Valve (BPV). Both release pressure from the intake system when the throttle closes, but a BPV recirculates the air, while a BOV vents it to the atmosphere (with a whoosh sound!).

Why Do We Need BOVs/BPVs?

When you lift off the gas in a turbocharged car, the spinning turbo creates pressure. Without a BOV/BPV, this pressure can surge back towards the turbo, damaging it. The BOV/BPV releases this pressure, protecting the turbo.

Do You Need an Aftermarket BOV for Your Subaru?

• Stock BPV is sufficient for most: The stock BPV on your Subaru WRX or STI is good for up to 20 psi of boost. Upgrading is only necessary for higher boost levels.
• Aftermarket BOVs might not be all sunshine and rainbows: While the "whoosh" sound is popular, aftermarket BOVs can have downsides:
• Rich running: Venting air to the atmosphere disrupts air metering, causing the engine to run rich for a short time. This can harm spark plugs and the catalytic converter in the long run.
• Potential leaks: Even high-quality aftermarket BOVs can leak, reducing boost pressure and engine performance.
• Tuning might be needed: To minimize rich running, proper tuning might be necessary, adding extra cost.

Sticking with the Stock BPV?

Here's good news:

• The stock BPV is well-suited for most Subaru turbos.
• Upgrading is unnecessary for most drivers.
• You avoid potential downsides of aftermarket BOVs.

Considering an Aftermarket BOV?

Here's what to know:

• Upgrade only if exceeding 20 psi of boost.
• Understand the potential drawbacks (rich running, leaks).
• Choose a reputable brand and install it correctly.
• Proper tuning might be needed to minimize rich running.

The Final Blow (Off Valve pun intended)

The decision to upgrade your BOV boils down to your goals. If you're staying within the stock boost range, the reliable stock BPV is a good choice. But if you're pushing higher boost levels, a well-researched and properly installed aftermarket BOV might be necessary. Remember, careful consideration and potential tuning costs are essential before making the switch.