I have seen the std. Dump pipe that simply has one pipe for both the wastegate and the turbo.

Is it worth me going the dump pipe with the seperate wastegate pipe that later joins back in to the exahust say 6cm's down?
This is supposed to minimise turbulence at the back of the exhaust wheel when on full boost???

Or does it make bugger all difference..

Also should I go a 3 1/2" or a 3"..

I've decided to go with D&T Performance Exhaust as they are the only people that can guarantee that it wont drone in the car.

The mufflers they use are huge straight through mufflers, he said they would also fit a resonator to it. He said that usually with a full exahust I will be looking at around a 18rwkw increase.

They also dyno the car before and after the exhaust so that you can see the difference.

I would like to know the same thing. Apparently the isolated wastegate type dump pipe reduces backpressure at the turbocharger discharge but at such a high velocity that these gases travel I would have thought that backpressure would be negligible... I could be wrong though.
Anyone with an explanation ?

True... but can you or should you fit a dump pipe to a std wastegate? I got told you couldnt or shouldnt cant quite remember which... i always thought that only external wastegates could be fitted with a dump pipe.
Or are you both running external wastegates?

The standard set-up (Garrett) runs an internal wastegate with a dump pipe attached to the turbo housing, but there is no barrier between the wastegate & turbo outlet.
What we are trying to work out here is that if we isolate the wastegate from the turbo oulet would we get large enough power gains to justify the cost of one of these modified dump pipes ? I believe the HKS dump pipes are around $1000.....

Ahhh i get ya now... well im sure you could have someone make a dump pipe for cheaper than that!! I know a guy here in nz that offered to make one for me if i could find out how to put one on the standard wastegate.. and that one was only $200 fitted... admitidly its not an HKS one but surely the differance would be minimal..