Why Subaru Designed Their BPV to Leak – What You Need to Know About Your Car’s Blow-Off Valve

As a car enthusiast, you might have heard about Subaru’s unusual decision to design a blow-off valve that leaks. The concept might seem counterintuitive – after all, shouldn’t car components be designed to operate flawlessly? However, there is actual reasoning behind this unconventional choice. In this article, we’ll dive into the technical aspects of Subaru’s BPV design and answer some frequently asked questions about this topic.

Blow-Off Valves Explained

First, let’s go over what a blow-off valve does. A blow-off valve, or BPV, is a valve that releases pressure from the turbocharger’s intake pipe to prevent compressor surge. Compressor surge is a phenomenon that occurs when the throttle plate suddenly closes, causing the turbocharger’s impeller to stall and produce undesired pressure waves. These pressure waves can harm the turbocharger and engine, leading to decreased performance and engine damage.

A BPV serves a crucial role in preventing compressor surge by diverting the pressure back into the intake system. There are two types of BPVs – recirculating and atmospheric. Recirculating BPVs release the compressed air back into the intake system, while atmospheric BPVs release the air into the atmosphere through a vented sound. Subaru’s BPV falls under the atmospheric category.

Why Does Subaru’s BPV Leak?

Subaru’s decision to design a BPV that leaks is due to the composition of their turbocharger system. The design of the Subaru turbocharger system features a ring-shaped assembly, known as a compressor cover, that is bolted onto the compressor housing. The BPV is mounted onto the compressor cover, and when the valve is opened, it leaks a small amount of air into the atmosphere.

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This design choice is intentional and is known as a "hybrid" setup. The hybrid turbocharger system allows for faster throttle response and increased turbocharger longevity. It accomplishes this by reducing the amount of pressure build-up in the turbocharger system during gear changes. The leaking of air from the BPV aids in the reduction of pressure, leading to an overall smoother operation.

Subaru designed their hybrid turbocharger system with performance in mind, and the trade-off of a small air leak was deemed acceptable for the increased performance benefits.

Identifying a Leaking BPV

It’s essential to recognize the signs of a leaking BPV to avoid potential damages to your engine. Signs of a leaking valve include a hissing sound during gear shifts or idle, a decrease in turbocharger performance, and black smoke coming from the tailpipe. If you suspect that your BPV is leaking, you should take it to a trusted mechanic to diagnose and resolve the issue.

Potential Solutions

If you’re a Subaru owner and unhappy with the design of the BPV that leaks, you might be wondering if there are any potential solutions to this issue. One solution could be installing an aftermarket recirculating valve that will recirculate the leaked air back into the intake system. However, this will require a modification of your vehicle and could potentially void your warranty.

Another solution could be to upgrade your turbocharger system altogether. If increased performance and reliability are your top priorities, investing in a higher-performing turbocharger system might be the best choice for you.


Q: Will a leaking BPV cause any damage to my Subaru?
A: While a leaking BPV won’t damage your engine, it can lead to decreased turbocharger performance and decreased fuel efficiency.

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Q: Can I replace my Subaru BPV with an aftermarket valve?
A: Yes, you can replace your BPV with an aftermarket valve. However, this will require a modification of your vehicle and potential warranty voiding.

Q: Will upgrading my turbocharger system fix the leaking BPV issue?
A: Upgrading the turbocharger system won’t directly fix the leaking BPV issue, as this is an intentional design choice from Subaru.

In conclusion, Subaru’s choice to design a BPV that leaks might seem unconventional, but it serves a critical role in their hybrid turbocharger system. Understanding the technical aspects and potential solutions of this issue will help you make informed decisions as a Subaru owner.

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Joseph Weaver

With a background in engineering and a passion for cars, Joseph brings a unique perspective to our blog. He's particularly interested in the technology and innovation behind Subaru's advanced safety features, and his articles on this topic are always insightful and informative. When he's not writing, he enjoys playing video games and spending time with his family.

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