Well, I have seen 3 different uppipes on my friend's STi. He had the Helix flex, TurboXS, and Perrin. He made 5 awhp more with the Perrin pipe since it produced the least amount of turbulance going into the turbine. Problem was, it took us damn near 5 hours to put it in. It is completely steel piping, no "flex" like the Helix and therefore is a little harder to mate up to the turbo if your engine has shifted and settled into the frame more. If you are looking for an "easier" install (all up-pipes are complicated intall), go with the helix. If you are looking for a bit more power, look to the Perrin. It really made no difference in spool time but it made his TD05 a bit louder.
- 2004 WRX