Motorsport Blow-Off Valves (BOV)

The choice depends on the sensor your car has

A recirculating valve sends the air back into the intake, ahead of the compressor. It is the mandatory version on cars with an airflow meter: if you dump already measured air to atmosphere, the ECU injects fuel for air that is no longer there and the car bogs on every gearchange. The version that vents outside, with the noise everyone knows, only works cleanly on cars with a manifold pressure sensor.

The adjustment springs

The pressure at which the valve opens is changed with the spring. A stiffer one holds the valve shut to a higher pressure, which is what you need when you raise boost. Too stiff, and the valve no longer opens at all, which puts you back where you started. Each spring has the percentage above standard written into its name.

Adaptors and blanking plates

Adaptors and spacers let you fit a valve to an engine it is not made for directly. Blanking plates do the opposite: they close off the standard valve outlet, when you move to another system or when you want to remove it altogether.

What it does not do

The valve does not bring power. It brings better response between shifts and it protects the turbo. The power comes from the rest of the kit and from the mapping.