I'd like to add to that . Over the last few seasons of racing ive sen 3 T3 Turbo failures and a T4 with all the same symptom , they smash the exhaust housing around the ring of bolts that secure the 3 sections together, none of these cars,An Escort Cos, 2 sierras and a Mk 1 escort turbo were using dump valves . I reckon a dump valve may have no performance advantages but safeguards the build up of stress behind the compressor. I now always use one , its not for the noise, i cant hear anything over the row the rest of the car makes anyway !!