I think this is the tube that connects the turbo to the intake. Is this correct? Whats wrong with the stock part and what will you gain by changing it? <P>Also, are the cats themselves restrictive? If you are going to install cat backs only seems like this with now be the bottleneck in the exhast and will net only a few horsepower. Is it worth it to change just the cat backs without changing the cats or downtubes?