will 03 STI headers and up pipe fit on 03 WRX if the answer is yes is it worth before i put them on my WRX should i cut them open and and take all the guts out to make them flow better

 

Yes they will if they are same shape impreza. What do you mean by cut them open?

You can get them ported, but it is worth paying someone who knows what they are doing, otherwise there is nothing to else to take out. If you have a bugeye then you will be replacing the cat in the up-pipe which is the main restriction, otherwise propably not much difference between the STI and WRX as standard.

 

i mean cut them open and take any thing out that stop the gases

 

There is nothing so not worth the effort. Like I said, get them ported and the gases will flow better, but apart from that leave them as they come.

BTW, it is a big job to change them, the up-pipe needs the turbo to come off so bank on a day. I've just stripped mine ahead of some ported headers arriving

 

cheers mate

 

up-pipe well worth it as no cat in the sti but headers are the same

 

The STi and WRX headers MY01 to MY05 are exactly the same so there is no performance benefit changing WRX headers for STi headers.
The WRX has a cat in the uppipe and you need an STi uppipe with no cat if you are doing it on the cheap. At that point your WRX will need a CEL fix which is not a lot of money.
Ported headers and matched performance uppipe all DEI wrapped with five new studs are £369 exchange and £75 if we are fitting.

 

what is a CEL fix

 

CEL = Check Engine Light

CEL lights up when a New Age is decatted, so needs a 'fix' to extinguish the annoying light. Can either be sorted in a remap, or there's a cheap bridging resistor mod you can do. The resistor is a few pence from the likes of Maplin, etc. Do a search and all will become clear...