I have an '06 STI. I know all about the accessport and DP will do the most for this car, but i also hear horrible stories with these mods. Boost creeps, ect. What I've done, Its a noticeable diff. and relatively inexpensive. I feel the car has enough power, and will spend my money on track days. Mod 1. K&N drop in filter with silencer delete and Samco inlet hose. Good Stuff ! Mod 2. Prodrive catless midpipe. Real good stuff !! ( Can feel the dif. ) Mod 3. Magnaflow 3 inch Cat back ( sounds just right with my set up ) not too loud, but loud enough ! Just shareing my simple mods with the rest of us newbies that dont want to spend $$$$$ on our cars, but dont want to be STOCK !:hsnono: The best mod by far is the Catless midpipe !!! No check engine light......Oh, stock cat back works real good with the Prodrive mid pipe as well. Good Luck !
Why not get a whole downpipe?? Midpipe change only 2nd portion of DP, and also it is only 2.5". Get some Invidia or Helix 3" DP. This will replace both sections of stock DPs and will remove two cats. This setup will net you the most power
If you are really worried/scared about boost creep, just get engine management now. Then, get some suspension works done. It will net you the most power gain.
I hate to say it, but I agree with the above posts too. The main reason that the DP is better than the mid is that dp removes the cat and lets the exhaust flow further before getting hit with a restriction, in theory allowing the turbo to spool better. A DP with the AP would yield more and probably cost about the same as a midpipe and axle back if you shop around. With the new AP 2.0 coming out there are quite a few AP 1.0 out on the market right now. But i guess the bottom line is if you are happy with the set up. If it works for you go for it!
Go used! I just bought a Helix catted DP, a Perrin cat-back and a AP v.1 for $1030... when I bought a similar set-up new for my bug-eye it cost me close to $2k.... Stage 2 for $1k is not bad.. Have to spend another $300 for a pro-tune but it'll be worth it.
I have the Perrin Dp, got it for $100. Its a 3" that covers both dp and midpipe. I got a boost gauge to monitor boost creep. I haven't had any issues.
You shouldn't have boost creep problems with a TD04. From what I understand, it is mostly the 2.5 block with VF39 that has creep issues. Haven't read a whole lot about boost creep on the WRXs period.
Im fairly certain that by now, the vf39 on the 06 is open enough to help allieviate the boost creep issue somewhat. You're going to get a creep if you're using a flatplate (ie stock) or divorced wastegate flange style downpipe. If you'd like to expand your powerband and give some ups to your butt dyno, just go for the downpipe. The cobb map is designed for it anyway isnt it? Besides, if you do have a creep issue, its generally going to be mostly a mechanical problem allieviated only by porting the wastegate out further. From what Ive been told, although I am not sure how much of this applies to the 06 builds, the 07 was fitted with a different IHI turbo (vf47 or something)...I am curious whether or not this was in an effort to improve the quality of the 39 (ie thicken the walls, open the WG) or what... Best of luck