Blow off valves are essential for turbocharged applications. If you’re planning to add a BOV to your setup, we’ll give you all the tips you need to know so you can choose the blow off valve that’s right for you. Watch the video or continue reading below to learn more.
What are Blow Off Valves?
Blow off valves are parts that disperse boost pressure that has been processed by the intercooler on its way to the throttle body. There are three kinds of blow off valves that have different ways of distributing that pressure.
Recirculating: these valves send the pressure back to the intake, then being recycled through the turbocharger. This prevents air-fuel ratios from becoming too rich with fuel and prevents turbo drag.
Atmospheric: As you might guess, this valve diffuses pressure into the atmosphere. Because of this pressure being released, it makes a high-pitched “pssh” noise that car enthusiasts love.
Dual Port: the dual port valves recirculate air into the intake piping and expel pressure into the atmosphere to reduce turbo lag but keep that fan-favorite sound.
How Do Blow Off Valves Work?
To give you a deeper look at how blow off valves work, we’ll start with how air pressure moves from the intake to the exhaust system.
Cold air moves from the intake to the turbocharger, which heats up the air, then the intercooler cools the air again before reaching the throttle body. Once the throttle body is hit with enough pressure, it will close. This causes a build up of pressurized air that has to go somewhere. That’s where the blog off valve comes in.
The blow off valve redirects the air away from the throttle body, either back to the intake piping or into the atmosphere. The rest of the pressurized air that isn’t dispersed by the blow off valve runs through the engine, releasing exhaust gases, and escaping out of the exhaust.
Sizing
As far as sizing goes, whatever suits your application is best. Most turbocharged vehicles will be well-suited for a 38mm. If you’re looking at a turbo smart application, a 52mm would be a better option. If you wanted something for a drag racing application where you’re running two turbos, you’ll need two blow off valves and the size will be dependent on the power you’re running.
Spring Pressure
The last thing you’ll need to look at for your blow off valves is the spring pressure. The reason spring pressure is important is if the blow off valve is held open, you will have some boost leak.
There are a number of tests you can do to make sure your BOV is running properly and the spring pressure is operating correctly.
When at idle, your BOV should be closed. If your valve is fully open or half open, you’re going to have some boost leak. If when driving the car, you hear a “stu, stu, stu” noise, there’s a problem with your blow off valve.
A blow off valve with reliable, responsive spring pressure is going to minimize boost leak, reduce wear and tear on your vehicle, and help you enjoy that enhanced driving experience for longer.
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