by Malcolm » Thu Jul 28, 2005 3:36 pm
I had the compressor housing rotated on my ct26 in my gt4. It's fairly easy to do, you just either remove the locating pin in the compressor housing, or you file a new keyway for it on the edge of the compressor backing plate on the center section (this is what I did).
Making the new bracket for the actuator is a tiny bit tricky as you have to make sure it doesn't interfere with the coolant lines, and that it puts enough tension on the wastegate that it doesn't leak!
On the gt4 there was only a small spot for the compressor outlet to point to, between the fan and the engine mount, so it would definitely be wise to decide on the position with the turbo still on the car, rather than just approximating.
2.5" might be a bit laggy, I don't really want to get into the argument of how much difference the volume of the piping makes, but I know that on a gt4 with a massive front mount (600x300x75) and 2.5" piping that I had a ride in, the guy reckoned there was hardly any lag but to me it felt like boost built very slowly, with no real kick as it came in, and probably didn't seem to reach full boost until well over 4K (on stock turbo). In comparision mine, with 2" piping and a much smaller vr4 intercooler hit full boost around 3,500 with a big kick, and that was on an upgraded ct26.
As far as material goes, stainless would be the best, as it wont rust, provided you use a low carbon content steel (ie 304L), as normal austenitic stainless steel will suffer from "weld decay" around welded joints and rust. Mild steel is the cheapest but you'd probably want to get it ceramic coated or similar to prevent rust (all mine + intake piping cost $130 to be ceramic + powder coated). Aluminium will never rust but it will more readily conduct hot air from the engine bay into the intake air and could fail due to fatigue if it is loaded frequently due to lack of joiners, hitting chassis etc under engine movement etc, will also probably cost the most to make