dump valves

[cm1179]

are these purely a novelty factor or do they give a true efficiency gain on the turbo?

the bloke i saw doing donuts in the snow in his punto gt in the tesco car park earlier seemed to enjoy the sound

 

[cm1179]

i remember about 10 years ago, an evo flying past me and changing gear and the dump valve was more like a very quick,short, screech not more of the typical woosh sound, sounded awesome and did make me jump, kicked out a lot of black smoke though lol