The original Ford recirculation valve has a diaphragm design that can collapse and cause boost leaks. It is also fitted with a spring only rated for standard boost pressure. Once an engine has been uprated with a higher boost pressure (typically 375bhp+), then the likelihood of the valve failing significantly increases. The following valves are an uprated piston type design to prevent against this. They also remove the annoying whine you get from the standard valve when on light throttle lift off.