Just had my Exhaust delivered and wondered how much gain in BHP will i get after fitting?

It is a T304 complete SS exhaust.

The car is 02 STI Type UK Prodrive standard.

 

I would say you are looking at an extra 10bhp at a guess. But does depend on any other mods you have already got installed. I have been told on the classic's exhaust and airfilter with remap or ecu should see a healthy 30 50bhp depending on what type of impreza it is. but unless you have a dino done before and after the mods wouldn't really know.

 

Without a remap, probably not a lot, as the ECU will try and maintain the status quo. You may get the odd boost spike though. With a remap a decat STi should produce in the range of 320-340bhp. When you say Prodrive, do you mean Prodrive style, or Prodrive performance pack, as both were available with the 02 STi IIRC.

If you don't already have the performance pack, you'll need to buy an uprated fuel pump prior to your remap, Walbro 255lph is the fav.

Ns04

 

You may not get more than 20 bhp, but without a re-map mine felt much nicer to drive, better pick-up at low revs, (sounded nicer !), revved out past 6500 rpm much more swiftly.
Then I got a re-map, to 340 bhp.... and on it goes , LOL

DunxC

P.S. I have a sports cat, so mine never boost spiked, but you will/may get a CEL as the cat efficiency isn't as designed by Subaru as standard, I ignored mine for 18 months...