3" SV if you don't have it yet. Just add the .63 housing (real easy). If you were starting out it would be more worth it. But for the money to change from a working setup it isn't worth it for a little more spool up. Actually if you have the header it may spool too quikly and just make you slower with wheel spin. If you bought the FWD hogged out 2 piece they ran the lower half to the gasket at the plenum. Thats bad to do if you keep the upper half. BUT its perfect for adding a plenum to the lower half and making more power. You already have enough parts for 400 HP+ or 350 at the tires. With a plenum and a S50 you would need 72lb injectors to make 500 HP or 400 WHP. Also the TU header is the size of a T4 turbine at the hole. When you get the .63 housing port it to match the TU housing, just doing this as bad as it is may make the .63 spool the same as a .48. So your really going to be in the 400 HP range and still be good on the street. With the TU header I find they need the turbine matching to the header and a short turn added to the turbine when it gets cut. Then the header need a little match porting at the head, and off to get hot tanked. Mine came with a small pile of metal shavings in it. All should be worth the trouble though. BTW you better port the wastegate hole in the turbine too, the new header will over flow the wastegate and make the boost creep. Tomarrow night I plan to port everything to match and will have pictures up soon on TD.