Subaru Forester Owners Forum banner

Frugal & more quiet turbo catback exhuast options

(All Years) 
4K views 16 replies 7 participants last post by  4x4hasi 
#1 ·
I'm in the midst of deciding how I should decrease the volume of my exhuast while maintaining or decreasing backpressure and would like some assitance. I'm only looking at altering the Cat-Back section of the exhaust system. Any thoughtful input/comments would be appreciated.
Current set up:
Invidia DW catless DP
3" Ebay "Cobb" knock off catback, original straight through muffler has been removed, in its place...
3" Flowmaster Series 50 chambered muffler (ended up not being any quieter than the original Cobb style muffler, just sounds different and likely adds backpressure)
And a 3" high flow cat welded in at the begining of the mid-pipe, right after it connects to the DP flange.

I have already purchased a 3" inlet 16" long resonator thinking I'll use it in my solution but am not married to using it.

Requirements in order of importance:
-As a point of reference, I had a catless DP with a Borla Hush on my 04 STi and though it was perfect at the time and it would be acceptable now but a hair louder than ideal for my current aging taste.
-Must flow better or at least no worse than my current set up and/or not hinder ~380whp
-Cheaper is better

Options so far:
1.) Weld 16" resonator in midpipe & weld old "Cobb" style muffler in mid-pipe as well, leaving the current flomaster muffler where its at (yes, thats 1 resonator & two mufflers) This is the most quiet option, but will it significantly add back pressure? Can a straight through resonator/muffler add much backpressure?

2.) Replace the flow master with the original Cobb style muffler and weld the 16" resonator into the mid pipe. The reason for this option is that I've read the chambered mufflers actually do add backpressure relative to a straight through muffler, hence this set up should decrease volume as well as increase flow... in Theory, but in practice?

3.) Buy another resonator, weld two into the mid pipe and replace the flowmaster with the original "Cobb" style muffler. This would cost another $40 in parts but *should* flow the best and give a low volume level. Could sell the flowmaster for a few bucks though...

4.) Buy a dnynomax VT muffler and just weld it in place of the flowmaster. Possibly add in the resonator I've already bought. Just did a little reading on these valved mufflers and they seem interesting but I've never had one or known someone who has. I think they're around $100+

Yes, I should have just bought a more stealth exhuast to begin with but I wasn't concerned with noise when I started modding this car. It didn't become a priority till recently. And now I can't bring myself to drop $600 on a new catback. Oh well, live and learn I guess...

Thoughts?
 
See less See more
#3 · (Edited)
That chambered flowmaster is GARBAGE. Trust me, no turbocharged car that wants good exhaust flow should ever even consider a chambered setup. Its about as free flowing as your stock exhaust. Whatever you do, make sure it involves getting rid of it.

I have something very similar to what you're running:
a totally re-shaped cobb knockoff exhaust with a custom resonator
See my build thread for details/pictures/sound clip.

I retained the original muffler and just added a resonator. Its still a bit loud for my taste I must say, but not as loud as before. Also going from a perrin catless to a helix catted downpipe definitely mellowed out the exhaust raspi-ness and made it a bit quieter as well.

A twin tip muffler like one of the borlas, stromungs, or maddads, with as big a physical size as you can fit under there, would be my choice. In fact I may be doing that in the near future on my car. It doesn't flow as well as a straight shot 3", but doesn't choke up nearly as bad as a chambered design. So IMO you get the best compromise between the two while keeping flow relatively good. MAGNAFLOW from performancepeddler.com has the biggest selection I've seen yet, just about any size/layout you can think of, and most of them are 70-110 shipped.

I have done a bunch of research on the dynamax VT, great idea, but have heard from more than a couple individuals that with time the little flapper/spring setup inside starts falling apart, or breaks, or starts making noises, so that is definitely something that keeps me from running one of those. Even OEM's like BMW that have this flapper setup in the exhaust have a ton of reports of them breaking down over time, making noises, and just not being reliable.


Just my .02
 
#4 ·
^-Great input 18psi, thank you very much. Would you say that adding the resonator reduced the volume by more than adding the cat did?

Any particular muffler you're leaning towards?


I'll check out the site you mentioned when I get some time here soon...
 
#10 ·
Stock pipe as in 2.5"? You will be giving up power with it, but I'm sure you already know that.



Hard to say, I think they both mellowed it down a bit, less raspy, more smooth rumble. Id say the cat did this more than the resonator though.
I'd go with the absolute biggest one that will fit. The site is kinda tricky to navigate, but definitely poke around there and look at the options. Go underneath the car and measure the dimentions around the muffler. Then go with whatever will fit without hitting anything. More packing = less sound. Twin tip exit splits the exhaust flow and cancels out a bunch of the noise.
 
#9 ·
The Magnaflow comes in all sizes & this would be a custom installation, so no matter the size exhaust pipe you want, your trusted muffler shop could build what you want. :wink:

As for me, even with my up coming power MODs, I'm staying with the stock pipe with an aftermarket resonator (basically a glasspack) & the Magnaflow muffler. :cool:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 
#12 ·
Just listened to 18psi & Bobby's clips, both sound great. Much more subdued than mine. Think I can tell a difference between the magnaflow sound and the cobb imitation muffler.... Decsions decisions....
 
#14 ·
It all adds up! I thought that 18psi's sounded a little "sharper/raspier" than Bobby's and it seems like that might be due to the cats that Bobby has and 18psi does not.

Good call guroove!
 
#15 · (Edited)
Follow up: I got my cobbled together exhaust welded up today and am very pleased. I ended up buying an additional resonator (2 total) and re-using the cobb style muffler with an o-too-long resonated tip welded on to it. I would prefer a magnaflow but didn't want to throw any more money at my frankenstiended exhaust system. It's much quieter than before, most noticably on the freeway, no more drone! I think the tip sticking out 2-3 inches past the bumper helped with this maybe?

Here are the pieces I had installed:


All straight through types:


I'll try to get a video clip tonight and post it.

Final costs (a little high):
Cobb style exhaust $200 shipped
2 resonators & 1 resonated tip $110 shipped
1 high flow cat $50 shipped
Installation $100
Total: $460. That's about the cost of a used Hush/whisper but this is more quiet than I remember my Hush being. Plus, I also have a cat which wouldn't come with a Hush/whisper at that price. I'll count it as a small victory :biggrin:

EDIT: Just took my wife for a spin and she was even pleased! Said we could now drive her Grandma around....this might be turning into a loss :icon_wink:
 
#16 · (Edited)
Here's a poor vid/sound clip. Turns out my phone doesn't capture exhaust audio well at all. Sounds MUCH louder in this vid than it really is. For perspective, notice how loud my foot steps and my door opening are before I start the car:


On a different topic, notice the sounds of my turbo when the exhaust sound fades. I've never heard another turbo that sounds so much like a supercharger, it really wines when there's no load on it. Sounds normal as soon as it starts to get close to positive pressure. Tuner said he hasn't heard anything really like it before but the turbo has no play, spins freely, made good power and holds 15psi to redline. It's been this way since I put it on, about 10,000 miles ago, with no change in perofrmance. Any thoughts why it sounds like it does??
But it will be off shortly, soon as I get the HTA rebuilt :icon_biggrin:
 
#17 ·
i was reading through these posts. i am debating to change my complete exhaust as well now totally stock. i came across 02-07 WRX & STI Megan Racing Type-2 Black Cat-Back Exhaust plus the matching megan racing down-pipe. i found several sound clips on youtube...very quiet rumble...i think im going to settle on this set up. 3" all the way total cost arround $500 plus install. what do u guys think?
 
You have insufficient privileges to reply here.
Top