Searching is your friend. I had (have) the same question, although I want my exhaust to be rather understated and as quiet as possible.

Here's the high level of what I've found - get a downpipe and a tune, then add mods from there, re-tuning if you install more performance parts. For instance, if you later want to add an aftermarket uppipe and headers, then a retune might be necessary.

I think the word "tune" will come up in a lot of people's comments. Also, louder doesn't mean better....

 

Modding an STI is in no way like modding a mustang. A catback exhaust will be 95% sound and 5% power. So you have to ask yourself do you want more power or more sound. If you want more power, pick up an Access Port and a downpipe. If you want more sound pickup a catback.

Do lots of searching as every question you will ask will have already been answered numerous times.

 

Hey man, I use to have a Mustang and after that an Accord that were both highly modded. Word from experience, do NOT mod the STI like any car you have ever touched before. The ECU on the STI and the entire system is completely different that what you are use to seeing.

You don't get immediate and big gains out of the STI like you did with the Stang just by upgrading the header, exhaust, throttle body and intake system. Each one of those mods on the STI will require as it was stated earlier, an ECU remapping. The STI doesn't learn and adapt like the Stang does.

First step would be to get some engine management. best forst choice IMHO is the Cobb AccessPort. Go to Stage 1 with that. Then get a Turbo back Exhaust and go to stage 2 with the access port. Outside of that, any modifications made to the STI will require you to take your ride to a tuner. Best idea with that is to save up and install a majority of your parts at once and then get a tune.

Stay away from the blow off valves, cold air intakes and turbo timers until you know what you are doing.

 

Go for a full TBE (turbo back exhaust) and a cobb AP v2 (v1 if you want to save some money i suppose). For the TBE you will have to have the cobb AP, or some sort of EM/tune. From that point, which is roughly considered stage 2, its a good idea to talk to a local tuner and search these forums for your next few upgrades as each one will require and effect another.

Stage 2 is a good start though.


For exhaust sound/loudness refer to this thread :

http://www.iwsti.com/forums/engine-power-performance/72486-exhaust-loudness-thread.html

And your best friend is that search engine on these boards.

 

please search.... if you want loud^^^^ link above and also herer

http://www.iwsti.com/forums/engine-power-performance/72486-exhaust-loudness-thread.html

 

buy my helix catback!

 

I want pics/specs on the GT/CS plz........ Talked with a guy who had one while stuck in traffic and he told me it had a 5.4 liter..BS? It sounded mean as hell so he could be legit. It also had Lambo doors which normally I'd be heavily against, but looked good in this case...

 

The GT/CS should have the 3 valve 4.6L in it, unless he did some type of swap. As far as I know, the only Mustang with the 5.4L is the GT500..

OP, good luck with the STi.