The iconic vrooom pshhhhh! sound from a blow-off valve that you hear down the street after a car shifts is like music to any car enthusiast’s ears. Many often wonder, does the WRX/Sti have a blow off valve?
Both the Subaru WRX and Sti models do not come standard with a blow off valve (BoV). Instead, they are installed with a recirculating bypass valve. A bypass valve is much quieter and cannot be heard when the car’s engine components are stock or oem.
One of the first modifications that someone does to a Subaru WRX/Sti is installing an aftermarket exhaust, a cold air intake, and an aftermarket blow off valve. What some people don’t understand is that a bypass valve and blow off valve are actually two different pieces. Let’s take a look further at the similarities and differences.
What Does a Bypass Valve Do?
When an engine is fitted with a turbo charger, this will cause increased internal pressure and combustion. Another name for this is forced induction. A Bypass valve or blow-off valve is needed as a way to release the pressurized air when the throttle body is closed.
If there isn’t a way for this excess pressurized air to escape, then the air will end up escaping wherever the least resistance is. This is usually straight through the turbocharger itself.
This can cause a number of issues and can destroy your turbocharger, engine, and other components. The term for air escaping through your turbocharger is called turbo flutter as their will be an audible fluttering sound as the turbocharger chops up the air instead of pushing it through.
A bypass or blow-off valve is a very important piece and will ensure that your turbocharger system is going to perform and work properly.
Do Aftermarket Bypass Valves Need a Tune?
Installing a new or aftermarket bypass valve will not require a tune. A bypass valve is a valve that recirculates air as a way to prevent turbo flutter or compression surge. This means that it is not releasing any excess air, since it is just recirculated back into the system.
If you know about turbocharged engines, then you know how important it is to have a tune when new performance pieces are installed.
Adding more ways for your car to get or release air will usually mean you will need to tune your car for it to be able to utilize the extra air and make more power.
The more air you make your car take in, the more air you will need to expel. The more air that you can force into your engine, the more power your car will make with the proper tuning. This is the general consensus of how a turbo charger increases engine power.
Can You Add a Blow off Valve to a Wrx/Sti?
In order to add a blow-off valve, you will need to remove and replace your car’s bypass valve. All makes and models of the Subaru WRX/Sti come standard with a recirculating bypass valve. If you want to add that cool sound of the pressurized air escaping from your car, adding a blow-off valve will give you that.
Instead of the air recirculating back into your car, a blow-off valve vents the air to the atmosphere. This is why their is a loud and audible hiss sound when the throttle body becomes closed as the air rushes to escape out of the valve.
Most of the time, adding a blow-off valve, is a simple process. Simply locate where your current bypass valve is, remove a few bolts, a hose, and install the new blow-off valve.
There are many aftermarket brands that sell blow-off valves that are compatible for the WRX/Sti.
Each generation of WRX/Sti will have slightly different blow-off valves, so always be sure you are buying a piece that is compatible with your specific year, make, and model.
Best Brands for Blow-Off Valves
Perrin
Perrin Performance is a common aftermarket brand that WRX and STI users use for blow-off valves and more.
HKS
HKS is another great aftermarket brand that sells blow-off valves for the WRX/Sti. Their blow-off valves have very unique sounds that many WRX enthusiasts love.
Boomba Racing
Boomba Racing was most popularly known for their 2015+ WRX recirculating bypass valves, but they also have a wide selection of blow-off valves.
To check the current prices and availability of Wrx/Sti Blowoff Valves, click here to view the selection on Amazon.
What Does a Blow off Valve Do for a WRX/Sti?
In short, a blow-off valve is a piece that helps regulate air pressure in the engine. Unlike a recirculating bypass valve, a blow-off valve allows the air to actually escape to the outside, or the atmosphere. This is what creates the loud iconic whoosh sound that you hear from turbo-charged engines.
A blow-off valve helps release engine pressure and prevents boost creep and compressor surge. Boost creep is when the engine has built up pressure past what the predetermined level has been set to.
Does a WRX/Sti Blow off Valve Need a Tune?
If you add a blow-off valve to your WRX/Sti, you will definitely need to get a custom tune. Your car may still run, but it is not recommended to drive your car without a tune as you can damage your engine over time.
The WRX/Sti both come standard with a recirculating bypass valve. This means that the air pressure is recirculated back into the engine and is not released.
However, when adding a blow-off valve, this changes the air to fuel ratio because air will be released from the engine into the atmosphere.
Many blow-off valves also have an adjuster on it on how much air pressure to release. If this is done incorrectly, your car can create either a too rich or too lean condition.
Getting a proper tune from a professional tuner will help alleviate any rich or lean issues you may encounter by installed a blow-off valve.
Frequently Asked Questions
Does No BoV Damage Turbo?
If there is no bypass or blow-off valve installed on your turbocharged car, the accumulated air will be forced to be released through the turbo.
This will cause compressor surge and turbo flutter as the air is sent through the turbo instead of being recirculated or released by a bypass valve.
Over time, this can be detrimental to your turbo which can cause other engine components to fail along with it.
Does Adding a Blow-off Valve Void Warranty?
Adding a blow-off valve will not directly void your warranty.
However, if the dealership deems that your blow-off valve was the reason for an engine component breaking, then your warranty will be voided.
Does BoV Increase Power?
Adding a blow-off valve will not increase the power of your car. A blow-off valve is a way for your cars turbocharged system to release the extra air pressure, or psi, instead of it going back in through your system and damaging it.
The more air pressure your car creates, the more air will have to be expelled. Many high horsepower cars need blow-off valves to release the high amounts of air pressure to prevent damage to their engines.
Final Thoughts
The WRX/Sti does not come standard with your traditional blow-off valve, but instead comes with a recirculating bypass valve. This valve is used to redirect pressure from the turbo so it doesn’t cause turbo flutter or compressor surge.
Adding an aftermarket blow-off valve to your WRX/Sti is definitely possible by purchasing it from a reputable brand like HKS, Perrin Performance, or Boomba Racing
If adding a blow-off valve, be sure to get a tune from a reputable tuner to make sure that your car will run properly and be within parameters when it comes to air/fuel ratios,
