One of the most important additions you can make to a turbocharged engine is the installation of a turbo blow off valve. While many factory turbocharged vehicles will come with a BOV from the factory, they are not commonly included in most low-boost aftermarket turbo kits. While they are not absolutely required in these low boost situations, a BOV is a good idea for any turbocharged application.
A Question of Performance and Durability
Turbochargers can introduce large amounts of pressurized air into your engine. When your throttle plate closes however, this airflow has nowhere else to go but backwards, which sends it back towards the compressor. This pressure wave tries to reverse the rotation of the compressor which at times can be spinning at many tens of thousands of rpms, and the resulting stress can cause failure of the bearings or the turbo itself. What a blow-off valve or recirculation valve does then, is give this pressure wave a place to go, reducing stress on the turbo and improving response. While this compressor surge can be more of an annoyance than a danger in low boost applications, it still can dull boost response. In high boost applications, this compressor surge as it is called, can cause outright failure.
Who Needs One
Everyone with a turbocharger-equipped engine should have some form of relief valve installed for both longevity and improved performance, especially in the case of daily street driven vehicles. There should be some care taken when selecting one however, especially in vehicles with a mass airflow system. Installing a vent-to-atmosphere type of BOV or VTA BOV will cause incorrect air readings and overly rich idle, stumbling and stalling problems. MAF equipped vehicles should always have their BOV properly recirculated back into the intake tract to prevent these problems.
While a BOV may only seem to help response in low boost applications, in reality, a properly installed BOV can vastly improve longevity in low and high boost applications alike. The simple answer to this question then is that all turbocharged vehicles should have a BOV installed for best results.