Subaru Archives - Automotive Nerd

A blow off valve can be bad for your WRX/Sti. Without a tune, running a blow off valve can cause your car to either run too rich or too lean depending on the settings of the blow off valve. A car that is running too lean can be very dangerous and detrimental to its engine. When fuel ratios are too lean, a car is more prone to knocking and engine detonation which is one of the biggest concerns for turbo charged cars. The WRX/Sti come standard with a recirculating bypass valve. This valve recirculates the air pressure inside the engine instead of releasing it like a blow off valve does and does not alter the cars fuel trims. What Is a Blow off Valve? Click Image for More Info The main purpose of a blow off valve is to release internal pressure in a turbo charged engine. There is also a loud unique sound when a car's throttle body closes. You will hear a loud pshhhh sound as the air quickly escapes from the blow off valve. If you're a car enthusiast, then this sound will literally be music to your ears. However, a blow off valve isn't used to just make your car sound cool. A Blow off valve helps protect the turbo and engine from extreme pressure which can cause compressor surge and turbo flutter. Compressor surge is when air pressure escape through the turbo, and turbo flutter is the sound that is made when it is being chopped through the turbo. To check the current prices and availability of Wrx/Sti Blowoff Valves, click here to view the selection on Amazon. Does a WRX Blow off Valve Need a Tune? It is highly recommended to tune your WRX/Sti if you are adding a blow off valve. A custom tune will allow your car to run at peak efficiency and performance without issues to your car's air to fuel ratio. A perfect air to fuel ratio is 14.7:1. This is when all fuel burns with no excess air. A tune is required due to the fact that these cars come standard with a recirculating bypass valve. A bypass valve keeps all the air inside the engine and recirculates it. A blow off valve actually releases or vents this air pressure to the atmosphere. The pressure that leaves your car was accounted for by your car before it ever left the engine. This can trick your engines computer into running too lean or too rich as it will have to modify the fuel trims for the loss of air. A car that is running too lean is more dangerous than a car that is running too rich. Both of these fuel states in your car has its pros and cons. Can a Blow off Valve Damage Your Engine? Over time, a blow off valve can damage your engine. The issue with a blow off valve starts with the air being released out into the atmosphere. The air that is being dumped out has already been measured by the MAF sensor/ECU and your car's ECU is responsible for maintaining the correct fuel to air ratio. This can cause your car's ECU to add fuel for air that is no longer there which can create symptoms of running too lean or too rich depending on the other modifications that your car has. Symptoms of a Car Running Too Lean Some signs that your car may be running too rich can include things like worsening gas mileage, car backfiring, spark plugs fouling, premature wear of the emission systems, foul smells, or black smoke coming from the exhaust. Symptoms of a Car Running Too Rich One of the main symptoms of a car running too lean is knock. Engine knock occurs when fuel ignites before it reaches the right moment. Knocking can damage the piston, cylinder walls, and even the crankshaft bearings. A few other symptoms can include clean or white spark plugs, engine not starting, and poor performance. What Does a Blow off Valve Do? A blow off valve simply releases air pressure that accumulates from your car's turbocharger. This is to help prevent any type of compressor surge or turbo flutter. A blow off valve being added to a turbocharged car must be dyno tuned so that the proper air to fuel ratios are properly accounted for. Does Installing a Blow off Valve Void Your Warranty? When it comes to warranties in the world of cars, there are a lot of loop holes. A warranty is usually only valid if the car has not been modified, but in most cases the modified part or piece has to have caused the failure in order for it to void your warranty. For example, if your car's starter goes out within a certain amount of time, it may be covered under warranty. If you have a blow off valve installed, this won't directly interfere with getting a new starter since a blow off valve would not likely affect your car starting or the starter. What Are the Cons of a Blow off Valve? A few bad things about a blow off valve are premature engine and component wear due to your car running too rich or too lean without a proper tune. A blow off valve may void your car's warranty if it were to go bad and somehow affect other engine components like your turbocharger. If you don't know how to install a blow off valve, you will need to pay someone for the labor. Are Blow off Valves Worth It? A blow off valve being worth it based on personal preference. Many car enthusiasts will say they love the added sound of the air being released by the blow off valve, which is strictly for vanity reasons. Others may actually need a blow off valve because they have a highly modified WRX/Sti that needs the air dumped to the atmosphere to prevent turbo and engine damage. However, if you are planning on adding a blow off valve to stock car to improve performance, steer clear. Adding a blow off valve will not add any additional horsepower to your car. Final Thoughts A blow off valve can be bad for your WRX/Sti if the proper safety precautions aren't met. Be sure that the blow off valve is installed properly so there are no boost leaks, and also be sure to get a tune to make sure your car operates correctly. It is very important for your car to be running with the proper air to fuel ratio to prevent a state of either running too lean or too rich. Overall, if your car is stock, a blow off valve is not worth it. It can cause more harm than good if it is not properly installed and accounted for with a tune.