yea somebody said if i change the spring in the waste gate my turbo will respond fasternot too sure bout that

 

Increasing the wastegate psi spring will keep the wastegate shut longer and spool will increase. Pointless unless you are running a much larger turbo like a 2871r or larger. Running a mbc will have the same effect since it delays the signal to the wastegate also.

 

On your B6 A4 there is not a "spring" per say in your wastegate. The wastegate actuator is a diaphram that works on vaccum to open the wastegate. It is what it is and you can't change it. but you can do what cincyTT says with an MBC or even running and N75H valve that hold higher boost levels. But those are items that are not part of the wastegate; they just control when it opens.
Many running an N75H with no ECU upgrades get overboost CEL's though. Like an MBC with stock ECU, it shouldn't work very well unless your ECU has a chip. But cincyTT says his works, so I'll go with that.
Needless to say, though, there is nothing in the wastegate or wastgate actuator that you can change on our B6 cars.
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for a stock actuator you have to tighten the wastegate (not recomemnded) with the nut on the wastegate arm. You do that and the turbo will get out of it effenciency range and burn up really quickly, thats why its not recomended.