What Is a Blowoff Valve?

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By Isabel Prontes
eHow Contributing Writer

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Blowoff valves are pressure release systems that are inside of turbocharged engines. Blowoff valves function to prevent compressor surge from occurring and to lessen the chances of engine wear. They are one-way valves that open the atmosphere up to above a certain pressure that is already set. This is done in order to relieve buildup in internal pressure. Blowoff valves are sometimes called pressure-relief valves or hooter valves.

Identification

Blowoff valves release air into the atmosphere. In doing this, blowoff valves produce a very identifiable sound that many in turbocharged sports cars experience. Many people appreciate this unusual sound, and some blowoff valves are even sold with trumpet-shaped kits that enhance the hissing sound.

Warning

Many people purchase blowoff valves for the sole reason of hearing the distinctive hissing sound. There are some laws that make it illegal to release "unmuffled" blowoff valve sounds. In the United States, Australia and many parts of Europe, it is absolutely illegal to to have a car with unmuffled blowoff valves.

Considerations

There are also some drawbacks to blowoff valve sounds. In vehicles in which the blowoff valve is placed after the mass airflow sensor, releasing the sounds to the atmosphere can confuse the engine's ECU (engine control unit), which can lead to the engine stalling or hesitating when the throttle is closed. Higher boost pressures can exacerbate this situation and make it worse. This can ruin catalytic converters and foul spark plugs, which can lead unburned fuel to combustion and melt the converter.

Function

Blowoff valves function to stop compressor surge. Compressor surge happens with the lifting the throttle off a turbocharged vehicle that either doesn't have a bypass valve or has one that doesn't work properly. When compressor surge occurs, drivers will notice an unusual fluttering sound.

Vendors

There are a lot of online vendors that sell blowoff valves. Some good places to check on the Internet include 360 Tuners, HKS USA, Super Street Online, Turbonetics Inc., Cox Import, StreetUnit.com, The RPM Store, Race Inspired, Jazz Pro Parts and many others.