Dump valve

I have limited experience of turbo engines (but its exciting finding out how cheap and easy it is to get major power hikes )......what will a dump valve do for my GTA turbo, is it worth buying and will it improve acceleration, power or what????

The GTA has got a closed loop dump valve as standard, meaning it 'dumps' back into the intake system, so you cant hear it. It wont improve performance unless (a) the original one is leaking, or (b) your running say 14psi and the original one cant hold the pressure. Don't go for a normal diaphragm dumpvalve, go for a piston type..more reliable and better made. Normally £60-110 depending on brand. The Bailey one at £85 is the best, fully polished alloy and will dump into the atmosphere and make the great 'tissssshhh' sound. For £110 you can buy a Bailey Closed loop dumpvalve like the original...no sound but more reliable.

Bear in mind that a dump valve doesnt actually increase power tho'.

All it does is prevent the build up of gases occuring in the intercooler/plenum area (which has the effect of slowing up the turbo spin rate) when the throttle is shut during a gear change.... thus keeping the turbo spinning. The idea is that it then ensures that there is immediate boost pressure when you open the throttle again...

Does that make sense?

Theres an age old dispute about to have a dumpvalve or not. In some ways Ruperts' right in that the turbo keeps spinning, so all your excess boost goes straight out the dump valve. If you dont have a dumpvalve the only way the boost can go is backwards through the turbo, slowing it down, but...it takes time to release meaning there is actually still some pressure in the system, instead of it being dumped straight off. So which is better for lag?! Manufacturers fitted them because they were wary of compressor shatter, where the boost goes back through and shatters the blades, but this can only happen on really high boost applications. On the GTA's, if you plug up the dump valve outlet, you get a lovely 'flutter' note on back off.

Ah well....I'm reliving old posts due to boredom....and drink!!! My dunp valve ot the minute, which appears to be the standard plastic bosch item makes a lovely flutter oin lift off (I actually lift off more often because of it!!!), is there something wrong with it??? If it is long in the tooth, am I losing power because of it?

If you get a flutter from your turbo when you let off, its normally due to a very stiff spring in a dump valve. Instead of the boost releasing through the dumpvalve, its going backwards through the compressor wheel, and the noise your hearing is the turbulence of the compressor wheel spinning in the opposite direction of the boost. Seeing as you have a standard dumpvalve which arent stiff at all, it could be sticking. The plastic plunger inside doesnt have a very linear up and down motion and can move and get stuck against the inner wall of the casing, so in the best case it could be sticking closed and not losing boost, and in the worst case sometimes sticking open and letting it all leak out!

I'm getting a fluttering noise also (which I had assumed was normal until I read this post) - is it possible to sort the dump valve or are we talking about a replacement item?

I can't guarantee that your fluttering dumpvalve could be faulty, but it is an over 10 year old piece of plastic crap. The diagphragm inside has no real linerarity and the springs can fail.