Quote: Originally posted by S600HBY on 11 March 2003
All turbo cars have dump valves, standard dump valves recirculate air back into the inlet where as atmospheric dump valves dump it into the air hence the whoosh sound on lift off. Not a real performance gain just sounds good if you like that sort of thing.
Not true I dont think. Not all turbo cars have dump valves. Modern ones, yes, but older models didnt get them from the factory.
They have a more useful function than just sounding good! They release pressure from the turbo upon lift off of the throttle (whether it be to the atmosphere with a whoosh or back into the system). All the air rushing through the turbo on acceleration all of a sudden has nowhere to go when you let off. If a dump valve wasnt there to release it, it goes back through the turbo. This has two main effects, one immediate and one long term.
Immediately this can cause the turbo to "stall" and can cause turbo lag when going back on the accelerator as it has to spin up again. A dump valve lessens this effect somewhat and is why people say they "help" with performance - keeps the turbo spinning and therefore hopefully boosting sooner when going back on throttle.
More importantly, if the pressure goes back through the system, it is a hell of lot of pressure on the turbo fins. Over time this can weaken them and cause failure. Therefore dump valves help with the longevity of your turbo.