What is a blow off valve and what does it do?

Have you heard a turbocharged car make that hissing noise when the gear is shifted? That’s the blow off valve doing its thing!

A blow off valve (or dump valve as it's sometimes called) is a pressure release system used in most turbocharged cars. While most modern turbocharged cars come with a factory-installed blow off valve, it started as a popular upgrade for car enthusiasts long before they became standard.

Let’s take a look at what a blow off valve does and who actually needs (or can have) one.

What does a blow off valve do?

To put it simply, a blow off valve helps relieve pressure in the intake. With the power generated in a turbocharged engine, all that pressure can cause significant damage and potentially be dangerous if not released properly.

How does a turbo blow off valve work?

How it works is a little more complex. A turbo blow off valve is located between the air take and the throttle body. When the throttle is closed, the pressure in the intake manifold increases, which triggers the blow off valve to open and release pressure.

Then when you accelerate, your throttle opens, allowing more air pressure to build and give you more power.

Are blow off valves bad for the engine?

Blow off valves are not bad for the engine. In fact, they serve an important purpose in turbocharged cars by preventing excessive pressure buildup. However, improper installation or using a blow off valve not designed for your specific engine can cause issues.

Does a blow off valve increase horsepower?

Blow off valves themselves do not directly increase horsepower. Instead, they contribute to maintaining the engine's efficiency and prolonging its lifespan in turbocharged cars. By relieving excess pressure during gear shifts or throttle release, blow off valves prevent damage and maintain consistent boost levels, allowing the engine to operate optimally. This, in turn, helps preserve horsepower and ensures a smoother driving experience.

Can you install a blow off valve without turbo?

The short of it is—no. If your car has no turbo, there is no pressure build-up, so a blow off valve isn’t required—the engine sucks up the air instead.

If you like the hissing sound the blow off valve makes, you would need to turbocharge your engine and install a blow off valve.

Common blow off valve problems

The blow off valve handles a lot of pressure, so problems can occur. There are three common problems people notice when their blow off valve is not working,

There are many reasons these problems could occur, including split or loose hoses, problems with the pistons and the leak test not being performed correctly. This is why visiting an experienced mechanic can help you get to the problem quickly and effectively.

Can you put a blow off valve on a diesel?

We’ve mentioned petrol dump valves a lot. So, what about a diesel blow off valve?

The problem with installing a blow off valve for diesel is that diesel cars don’t have a throttle body. Without the throttle body, the dump valve can’t work. However, a diesel dump valve is still possible!

A diesel blow off valve kit will use an electronic controller to signal the change in throttle position, then using a solenoid (a type of wire coil) to open the valve when it’s needed. So yes—you can put a blow off valve on a diesel car, ensuring you use the right fit.

Need a hand?

Blow off valves can be quite complicated little parts. With the risks involved in dealing with air pressure in your car, if you’re in doubt, give a mechanic a shout!

Our mechanics at mycar can help with answering your blow off valve questions, as well as installing and repairing dump valves. With hundreds of mycar stores Australia-wide, you’ll always have an experienced mechanic close by.

Keen to learn more about car valves? Check out our blog about what your car’s PCV valve is and how it works to help you get the most from your car.