What does a fuel rail plug do?

Fuel rail plugs help prevent fuel from being returned from the pressure relief valve. This also eliminates low fuel pressure rail diagnostic trouble codes (DTC). Fuel rail plugs maintain available fuel pressure during full-throttle driving.

What does a race valve do?

The Race Fuel Valve (heat-treated stainless steel construction) replaces stock or a shimmed pressure relief valve. This valve helps maintain fuel rail pressure during high engine load conditions by completely blocking the pressure relief port (effectively eliminating fuel return to the fuel tank).