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Old 11-07-2015, 02:13 PM   #1
SeeeeeYa
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Default OEM '15+ WRX Exhaust: Thoughts and Revisions

The stock exhaust is adequately sized for stg2 STi level power. So it's good enough for a WRX with stock to modestly upgraded power levels... where like many I intend to remain.

A "fault" of my exhaust was, I didn't like the huge startup drone, nor the crass tone of the exhaust note. An STi intermediate pipe totally cured both. It became a quiet exhaust, too quiet for most, with a refined muscular engine signature underway. Perfect for me.

Having determined the muffler's internal structure from prior experience coupled with the WRX muffler's spot welding, I had to change something inside it... to remove the only post-cat restriction. The problem is, each of the dual exhaust pipes end inside the muffler... plugged with a spot-welded cup. The exhaust then exits, under pressure, through only a 3.5" section of perforations around 80% of the end of the capped pipe. Amazing to me, but it apparently lets the WRX meet specs.

Otherwise the WRX muffler is OPEN. Both tip pipes end in an open end section, the internal "baffle" is hugely holed and only serves to hold the three pipes securely. Virtually zero restriction... except for that capped tailpipe with a strainer on the end.

Using a 1.5" hole saw I removed the dimple opposite the end of the tail pipe. Then I used the same hole saw to remove the cap from the end of the tail pipe. A 2.5" aluminum disc, four screws, and some RTV and done. My unrestricted WRX muffler is still quiet and while my wife hears no difference at all, I note more boxer motor sound under power.

Next is that third cat and pipe.
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Old 11-07-2015, 02:55 PM   #2
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Pics?
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Old 11-07-2015, 03:00 PM   #3
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pics or it didn't happen
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Old 11-07-2015, 03:37 PM   #4
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Pretty straightforward... didn't think to take pic until nearly done. Figured it was self-explanatory.
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Old 11-07-2015, 03:43 PM   #5
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The muffler, like the entire exhaust, is tough SS. It ate two hole saws.
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Old 11-07-2015, 10:15 PM   #6
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So basically you gained access to the opposite side of the muffler facing where the pipe enters the muffler. Removed a spot welded perforated cover that sits in the path of the exhaust entering the muffler housing. Then covered the hole you drilled to gain access.
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Old 11-07-2015, 10:29 PM   #7
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Quote:
Originally Posted by 2gnt2wrx View Post
So basically you gained access to the opposite side of the muffler facing where the pipe enters the muffler. Removed a spot welded perforated cover that sits in the path of the exhaust entering the muffler housing. Then covered the hole you drilled to gain access.
Almost... except the cup welded into the end of the inlet pipe is not perforated. Only the sides at the end of the pipe are perforated.

The exhaust stream hits a dead end. Then it is forced to exit the perforations axially into the muffler body.

One can see where that end area is by looking at their exhaust tips... it's the dimple above the inside tip.

Last edited by SeeeeeYa; 11-09-2015 at 02:43 PM.
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Old 11-09-2015, 05:42 PM   #8
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this looks cool
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Old 11-09-2015, 06:07 PM   #9
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Sound clip? Great work!
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Old 11-09-2015, 06:27 PM   #10
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Any chance you've taken a look inside in the mufflers of the 2015 STi optional performance exhaust?
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Old 11-09-2015, 07:53 PM   #11
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I'm a little S L O W and having a hard time visualizing this, but very interested. Any chance for some macro shots and some crude MS Paint pointers?
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Old 11-09-2015, 09:59 PM   #12
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Quote:
Originally Posted by freebird_78 View Post
I'm a little S L O W and having a hard time visualizing this, but very interested. Any chance for some macro shots and some crude MS Paint pointers?
The exhaust enters the muffler at the opposite end of the muffler as the tips. He cut a hole next to the tips in a spot that lines up with the entry poing of the pipe. Hacked off the solid end of the "Cup" allowing the exhaust to flow straight through rather than being forced through the little holes that you can see in the pic.
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Old 11-09-2015, 10:02 PM   #13
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I haven't seen inside any WRX muffler but this one. My experience came from my '05 LGT, on which I made multiple revisions. I expected worse, actually, but found the new WRX has only one "restriction" in it, that plugged pipe. The rest of it is wide open.

As I've posted, the sound really didn't change much... with the STi pipe it was already significantly changed, and sitting still one can only inspect idle or revving, which shows no substantive change. Which to me is good. I like my exhaust now. And again, on the road under power there is only a slight change... after all, there is an open window and wind noise to compete with. But I can hear a difference because I listen for it, and it is good. There is no recording that's going to help.

And frankly, how could there be any question that unplugging the pipe would not decrease back pressure and increase flow? Everyone knows the OEM exhaust restricts power, and how could it not. The pipes are not the problem. The entire engine output is forced to stop, then exit sideways through a perforated tube... the measured area of these perforations is 4.75"x 3.5" times two, one per muffler. Doesn't take much imagination.

FWIW, regarding the LGT, one valued member then used my mods on his highly modded car after tiring of big loud pipes... and still made great power, but more stealthily. He lost a little compared to the big pipe, but he had enough to spare the few. Down at the WRX level this is all I need or want.

As for SLOW people? Look at your muffler. Note that above the inner tip there is a raised dimple approximately 1.5" at its base. That's where the exhaust ends. Behind it is the plugged pipe.

Everyone seems to want LOUD exhausts. I prefer engine music. But that's hard to come by if the engine is hidden behind multiple cats, trumpeting through a long un-resonated pipe, and stifled by a metal strainer inside a SS can. The STi I-Pipe shut the pipe up. The muffler is now free flowing. Progress.
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Old 11-09-2015, 10:05 PM   #14
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Quote:
Originally Posted by 2gnt2wrx View Post
The exhaust enters the muffler at the opposite end of the muffler as the tips. He cut a hole next to the tips in a spot that lines up with the entry poing of the pipe. Hacked off the solid end of the "Cup" allowing the exhaust to flow straight through rather than being forced through the little holes that you can see in the pic.
Exactly.
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Old 11-09-2015, 10:33 PM   #15
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Quote:
Originally Posted by SeeeeeYa View Post
Exactly.
So this means the exhaust is actually exiting a few inches above the tips or to the right/left?

Aren't you worried about soot build up? I mean my tips are nasty, I assume having the exhaust come out anywhere other than the tip means your going to soot up the bumper?
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Old 11-09-2015, 11:12 PM   #16
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Quote:
Originally Posted by Boggie1688 View Post
So this means the exhaust is actually exiting a few inches above the tips or to the right/left?

Aren't you worried about soot build up? I mean my tips are nasty, I assume having the exhaust come out anywhere other than the tip means your going to soot up the bumper?
Sigh.

Do I really need to post a pic of the cover in place??

Didn't think so. But I will.
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Old 11-10-2015, 08:52 AM   #17
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When I'm done the rears of the mufflers will be painted black. Meanwhile, here is what they look like with the access holes covered.

No idea why they look upside down but when clicked they display correctly (Left/Right).
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Old 11-10-2015, 09:06 AM   #18
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Old people have too much time on their hands.

Thanks for sharing, interesting though.
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Old 11-10-2015, 09:38 AM   #19
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Quote:
Originally Posted by Wireeater View Post
Old people have too much time on their hands.

Thanks for sharing, interesting though.
And some older people have experience that directs their time creatively... as opposed to looking to follow the mod-du jour.

You're welcome.
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Old 11-10-2015, 11:07 AM   #20
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Quote:
Originally Posted by SeeeeeYa View Post
When I'm done the rears of the mufflers will be painted black. Meanwhile, here is what they look like with the access holes covered.

No idea why they look upside down but when clicked they display correctly (Left/Right).
Whoops didn't realize you put a cap on it. When i read straight through, I assume you left it open. Cool mod. I'd do it, but my **** is already too damn loud with the stock mufflers.
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Old 11-10-2015, 01:06 PM   #21
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I was trying to accomplish the same thing sometime last year, by drilling holes in the internal pipe from the exhaust tip end. Couldn't drill a single that far in Wasn't willing to make holes in the muffler housing, so just bought a cheap catback instead. Good job!
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Old 11-10-2015, 07:25 PM   #22
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Default OEM '15+ WRX Exhaust: Thoughts and Revisions

Thanks for posting this I have a stock wrx catback for my FXT and will be doing this. I used my stock FXT resonated mid pipe with the wrx mufflers which got rid of a lot of the drone, will compare the Sti midpipe to that, in guessing it's larger. I was always disappointed that the wrx mufflers didn't give a better note higher in the rpm range/wot - did it help that?
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Old 11-10-2015, 07:56 PM   #23
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Quote:
Originally Posted by FleaDog View Post
Thanks for posting this I have a stock wrx catback for my FXT and will be doing this. I used my stock FXT resonated mid pipe with the wrx mufflers which got rid of a lot of the drone, will compare the Sti midpipe to that, in guessing it's larger. I was always disappointed that the wrx mufflers didn't give a better note higher in the rpm range/wot - did it help that?
Truthfully don't know... yet. Between work and whatever I haven't been able to just go drive it much yet. No time alone, in other words, to explore it.

That said, the little I have has shown a different note under power... a more distinctive boxer sound is all I could hear the very little time I've had it under power. But here in the city there's little opportunity for that. I'll need to get out on the roads to find out more. One thing's certain, it has to be different... it's the how that's yet to be discovered.

Do it. Maybe you can find out first. Quick and easy as these things go.
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Old 11-16-2015, 02:32 PM   #24
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Today, for the first time since the muffler mod, I made a few WOT pulls. Still in town so only the first three "gears" in S# were able to be used (which still made me waaaay illegal). Mid 60's F and clear high-pressure weather, 27% humidity, oil temp 190+, DA 1290 ft. Looking forward to colder air and lower DA.

I have nothing to quantify things, no logs or time-to-speed data... but I'm certain it is different in a good way. It ripped quickly to 6200, and the shift was the surprising part... it was harder than I remember it, and jerked my head back. Zero sense of tapering off up high... in fact, it revved so quickly in the upper revs that when I tried manual mode I couldn't catch it and almost hit the rev limiter.

Midrange on this '16 was surprising from the first, subjectively way better than the '15 was and I had no complaints with it. Power delivery has always been super smooth and linear, making me unable to grasp when others with MTs complain about poor upper-RPM power delivery. But now I can definitely say that this '16 CVT's power in the same range is superb.

There is no doubt in my mind that opening the tailpipe in the muffler has made the difference I note, for obvious reasons. Still drone free at startup, still quiet, an excellent exhaust note to me, and as restriction-free as this motor needs or I want (except for the 2nd cat ).

As soon as I can I'll see how it does at much higher speeds and with performance using launch mode. Like I said, I have no data, so it's all personal observation. But I've been doing this a Long time and trust my instincts. When I had the means all my data did the talking, so I understand skepticism. Here, however, it is simply a logical conclusion. YMMV
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Old 11-17-2015, 12:28 AM   #25
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Quote:
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....It ripped quickly to 6200....

....making me unable to grasp when others with MTs complain about poor upper-RPM power delivery....

The manual trans redlines at 6700. Up to 6000-6200, it's fine. After that it falls on its face. My guess is the CVT just sits it at peak HP (upper 5000 range, can't recall the exact spec). I shift mine at about 6000, and if it wasn't for the dip in power at ~4500 that the first few shifts fall into, it would work perfectly. I'd prefer to see the midrange dip fixed rather than the extreme top end, but either one would fix the issue.
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