Advantage of an Up pipe?
 

Car:- Impreza STI 05.
What is there to gain by fitting an Up pipe, are they over looked when replacing an exhaust system?

Reason I'm asking is that I'm having my remapped soon after buying a Prodrive downpipe cat, the rest of the system is decatted,green panel filter fitted, but was wondering about getting the up pipe done, but only if you gain any thing?

Will also be adding a uprated fuel pump, colder plugs too, anything else that would be a worth while upgrade?

Thanks
Daz

No need to change the up-pipe at this level, you'll only slow spool by fitting a larger after market one.

there is a cat in some up pipes
not in the 2.5l 06-07
sorry don't know about the 05
if its a 2l i think it will have
some one will know for shure

Daz, no cat in yours, only reason to change would be if you were going for something like harvey's flow matched headers/uppipe combo.

I am sure its the newage wrx with cat in the uppipe

The 05 STi should not have a CAT in the uppipe.
On its own changing the uppipe (even for a good one) will not make a big difference just a few bhp and similar foot pounds. There are benefits from changing the uppipe over the OE even on your car without a CAT but as 53WRX points out the best gains would come from ported headers and purpose designed/matched uppipe.
Unfortunately, many aftermarket uppipes have not been properly designed or manufactured and the performance of the uppipe is critical to getting a quick spooling responsive engine. The design of the uppipe you require will be determined by the turbo in use and your goals. One or two uppipes cannot cover properly the range of turbos and performance sought by Subaru owners so you cannot just go out and buy anything and cross your fingers hoping it will work. I have three basic two bolt flange uppipes in six actual configurations and two three bolt flange in four configurations. All currently £139 each, DEI heat wrapped with five new Subaru studs.
In short you will get a small but noticable benefit from a correctly selected uppipe only but a very noticable benefit from ported headers and matched uppipe. Quicker spool, greatly improved response, pull harder and further before getting breathless and probably an extra PSI boost on the same duty cycle.

WRX has a Cat in the up pipe, but the STI doesnt, so I believe

Thanks very much for the replies.

Seems like there isn't a lot to gain for the level of tuning I'm looking at.
I'll see what Mocom can sudjest, or maybe stick to what I have listed, should be a good end result.