At first I was just going to get a Cobb DP but now I heard our mufflers are REALLY RESTRICTIVE? Because I kinda of like that STi stainless steel tip
who told you that? the most restrictive part is the d/p, many people use a d/p and midpipe and keep the stock axle back
here are some measurements regarding pipe diameters: http://www.rs25.com/forums/showthread.php?t=36449 the oem muffler has baffels in it, so do many aftermarket ones (ie flowmaser, magnaflow, ect...) you wont see the same flow rate through a baffled muffler as you will through a straight through muffler (fart cannon). but it doesnt REALLY matter that much so i wouldnt worry about it unless you care to squeeze every single 1/10th hp out of your setup.
yeah, changing it out isnt really NEEDED, unless you want a different or distinct sound and a little better flow...
you dont have to, but it might make it easier to bolt up the new DP. i am not sure how cobbs DP work with the oem system, or with aftermarket peices for that matter. keep in mind the best exhuast on a turbo car is no exhuast. by going to larger diameter pipe you are allowing more gases to pass through the system which promotes spool. since the exhuast gases cool after the turbo they contract and less volume is needed. so you can easily get by with a smaller axleback/mid pipe than then DP. basically you can do whatever you want for a catback, a aftermarlet catback will make more power. but if you want stock looks you might be fine sacrificing 5-10hp for it. (and saving $$ by not buying it)
Good question. Anybody got anything against running a basic cobb stage II with a TXS stealthback with the stock axelback?
Shouldn't be much of a problem -- I ran 18psi on the stock turbo with a similar setup and an STi can for quite a while. I also ran it with the Cobb map for several months. However, the stock WRX muffler certainly IS a fairly large restriction. I've found that I could run several degrees more of timing up top and hold boost a bit easier with an aftermarket muffler (and stock everything else) based on testing I've been recently doing.
This is true. The stock muffler seems to be more of a restriction at high rpm. An aftermarket muffler will allow you to flow more boost, and tune for more timing at 5k+.
. FYI, that testing is on an stage 1 car. I can't say from experience how restrictive the stock cat-back would be with an aftermarket DP (stage 2 car). I'd venture to guess that it would have similar affects. IMHO, if your car is a DD, and you're on a budget and don't care about the sound, you don't need to purchase an aftermarket cat-back.
For Example: When dream and I both had wrx's he had full AP stage 2 w/ a catback I had up/dp and a mbc we did a couple chases and he slowly/barely pulled on me and he had the jump everytime. imo, keep the stock catback and buy something else cool!
worry more about upgrade path. imo getting a DP that mates up with the stock catback just means that you will have to replace both units down the road as your quest for more HP continues.
That is what the STi will have later this summer.... Been running a Stealthback with stock exhaust for ~2yrs, looking to tune this summer.
like 16.5 psi in 4th and 5th was what i would set it for so i think. sry it was a long time ago, but that sounds right.
