Hi all, i am wondering if i do a custom midpipe on my 05 STI exhaust , will it help with the performance? i don't want the exhaust to be too loud so that is why i am thinking of doing this way. Anyone have experience with this??? any suggestion will be greatly appreciated.

thanks

 

You mean, the pipe with the second cat right? It might work that way, but what if it's too quiet for your taste still, then what?

I'm sure you'll gain a little just bcuz you've eliminated one of the two cats but that still the OE
cat in there. your gain will not be noticeable. Which noise are you trying to avoid, muffler's or the spooling/sucking air sound?
spooling noise, is barely noticeable provided you are still on the stock intake and filter.
and i don't think you need to go custom for the midpipe, there's the Stromung 3CE or the 3rd cat eliminator, i think it mates up to stock. look it up then talk to a vendor who sells it then you can go from there.

There's also the TXS stealthback, wherein you get d/p and midpipe to mate up to an OE exhaust. this one comes with a high flow cat on the mid but none on the d/p. you'll get the rumble here but not as loud as a TBE and you'll notice some gain here too.

Whatever you do, don't forget EM, so as to avoid headaches that comes from here on end.
Good luck and i hope this helps you...

 

thanks for your reply, i will certainly look at some of the pipes u mentioned. As to answer your question, i am worry about the muffler sound because police in toronto are really cracking down on exhaust nowadays. I want some gains but without the rumbling sound that i will sure to get with TBE. I totally understand that i iwll probably get the most gains with TBE but i have got to sacrifice that now. I have one sitting here waiting to be put on(buddyclub racing spec III) but the noise is just like a cop magnet....

 

Get a downpipe with a high flow (or no) cat for the most performance gain. That will take you to the end of the current setup just past where the last cat is. If you want, you can also purchase an "intermediate pipe" that connects from the downpipe back to the stock muffler. That will get rid of the stock resonator, but it won't get you nearly the performance gain of the downpipe. I did both and kept the stock muffler and everything is quiet like stock. Doesn't sound aftermarket at all.

 

If you want performance without the sound get a 4" tuboxs downpipe with an electric cut out and keep the stock exhaust on thats what i run and when i got it dyno'ed i got a 26.4 whp difference with it open, it's the best way to go in my opinion. Oh yeah or this one. http://www.quicktimeperformance.com/Downpipes/wrxdp.php