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Old 11-17-2015, 01:54 AM   #26
dogtrumpert
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Quote:
Originally Posted by SeeeeeYa View Post
And frankly, how could there be any question that unplugging the pipe would not decrease back pressure and increase flow?
Could this lead to a P0420 CEL?
I get one occasionaly with a Q300 cat-back (MY15).
Subaru want the OEM cat-back fitted before they will test further, saying it's probably the decreased back pressure.
(nice tech guide topic by the way)
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Last edited by dogtrumpert; 11-17-2015 at 05:38 AM.
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Old 11-17-2015, 09:49 AM   #27
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Quote:
Originally Posted by dogtrumpert View Post
Could this lead to a P0420 CEL?
I get one occasionaly with a Q300 cat-back (MY15).
Subaru want the OEM cat-back fitted before they will test further, saying it's probably the decreased back pressure.
(nice tech guide topic by the way)
No. The P0420 CEL is determined by the two O2 sensors in our J-pipe, one before and one after the cat. Your dealer is stupid and/or giving you the runaround... unless there's more to the story.

No cat-back exhaust will cause a P0420 CEL. A damaged wire or sensor in the J-pipe will, as would a bad cat of course. Exhaust system "back pressure" or lack of same will not.

A wheel bearing has as much chance of causing that CEL as this muffler improvement does.

Here is a good description of what's going on relative to that CEL. https://allwheeldriveauto.com/subaru...420-explained/
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Old 11-17-2015, 10:30 AM   #28
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Watched a documentary about turbos recently that stated in a turbo system you don't need any backpressure whatsoever. As above, won't be that causing a CEL
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Old 11-29-2015, 07:55 AM   #29
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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.
I'm pretty interested in this part. I hate the loud dronyness on the stock exhaust on cold starts since I start my car early morning. Have any more details on that? Are you referring to the pipe with the resonator?

Quote:
Originally Posted by dogtrumpert View Post
Could this lead to a P0420 CEL?
I get one occasionaly with a Q300 cat-back (MY15).
Subaru want the OEM cat-back fitted before they will test further, saying it's probably the decreased back pressure.
(nice tech guide topic by the way)
I wouldn't take advice from anyone saying decreased "back pressure" is causing an issue.

Quote:
Originally Posted by acemastr View Post
Watched a documentary about turbos recently that stated in a turbo system you don't need any backpressure whatsoever. As above, won't be that causing a CEL
That's because there is no engine that needs backpressure.
Think about how stupid that sounds. Why would fighting the exhaust stream be beneficial?

Last edited by Andrew025; 11-29-2015 at 08:10 AM.
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Old 11-29-2015, 09:53 AM   #30
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Originally Posted by Andrew025 View Post
I'm pretty interested in this part. I hate the loud dronyness on the stock exhaust on cold starts since I start my car early morning. Have any more details on that? Are you referring to the pipe with the resonator?


I wouldn't take advice from anyone saying decreased "back pressure" is causing an issue.



That's because there is no engine that needs backpressure.
Think about how stupid that sounds. Why would fighting the exhaust stream be beneficial?
Yes, the system with the resonated STi intermediate pipe installed. Night and day difference.
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Old 11-29-2015, 11:50 AM   #31
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Question, could you see if there were any perforated pipes attached to the two outlet pipes?
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Old 11-29-2015, 04:07 PM   #32
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Question, could you see if there were any perforated pipes attached to the two outlet pipes?
Interestingly, while both outlet pipes terminate internally in the same chamber (separated from the single other chamber the inlet pipe terminates in by a hugely-holed "front" chamber wall... a necessary support for the three pipes) one of the outlet pipes has perforations but the other one does not. I assume this has something to do with Subaru's idea of sound tuning.

With the OEM mufflers modded as mine are, and the STi's resonated intermediate pipe, it works perfectly... and I'm guessing this was Subaru's originally intended product as other markets have a resonated pipe.

IMO, there is no auditory value in trumpeting pipes... it is the engine I want to hear. An unresonated pipe like our OEM WRX intermediate pipe gets in the way of that and, like an out-of-tune loud child in the front row, ruins the music.
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Old 12-01-2015, 09:47 AM   #33
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Do you have a sound clip? curious what this sounds like.
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Old 01-01-2016, 06:29 PM   #34
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SeeeeeYa- I'm very interested in your muffler mod (smart thinking) and the resonated midpipe, very little louder and better tone.

But I have ground clearance issues, something drags under my 2016 WRX unless I enter my driveway just so. After it warms up here I'll get under and check what's dragging. If it's the midpipe a larger one won't work for me. I tried to contact Nameless Performance to ask how much larger their midpipe is than stock but because of the holidays I couldn't get in contact.
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Old 01-01-2016, 07:34 PM   #35
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SeeeeeYa- I'm very interested in your muffler mod (smart thinking) and the resonated midpipe, very little louder and better tone.

But I have ground clearance issues, something drags under my 2016 WRX unless I enter my driveway just so. After it warms up here I'll get under and check what's dragging. If it's the midpipe a larger one won't work for me. I tried to contact Nameless Performance to ask how much larger their midpipe is than stock but because of the holidays I couldn't get in contact.
Clearance hasn't been an issue with me, despite still cringing over areas I found problematic in my lowered LGT. But the resonator is an inch +- lower right where it is.

I could not be happier with this exhaust now. Reading all the exhaust threads is almost amusing, with respect to drone. NO exhaust without a resonator will be free of drone, and the STi I-pipe is the perfect solution.

Then there are those installing J-pipes and front pipes... and still expecting commensurate gains with the stock catback. Sheer delusional folly. However, with these mufflers sheared of their capped ends a stock catback is then able to flow well beyond OEM limitations.

The boxer motor's signature is also now obvious without the crass influence of the OEM intermediate pipe's resonances muddying distractions.

I prefer to let my car's performance speak for itself... as opposed to telegraphing to everyone in earshot I have a loud exhaust, supposedly telling them I'm a badass. This one now has a great sound at low speeds but is all but silent (as far as I can tell) at roadway speeds.

But then I have a CVT, a game changer when it comes to exhausts. IMO the CVT makes an exhaust sound like a bawling calf too often, especially louder ones. Sure playing with the paddles can mitigate that, but who drives that way all the time. I don't. So while I definitely prefer all the attributes available with a CVT it also denies the pleasure I've always found in my cars' exhaust sounds. The joy of hearing the motor's song and wail as I play that violin isn't possible with a CVT... but so be it, the compromise is worth it for this fine car. It is powerful yet stealthy.

But make no mistake... were I to be driving an MT again? It would have an exhaust more worthy of this motor's lungs. So far the Corsa sounds best to offer that music to me. Meanwhile, mine is perfect.
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Old 01-01-2016, 10:02 PM   #36
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Based on what I've read on this site; the FXT midpipe is smallest in diameter (if so, is it smaller than the stock WRX midpipe?), the STI is in the middle and the Corsa is largest? It's only supposed to be 10 degrees Fahrenheit here tonight but I'm getting excited about this and think I'll slide under the car tomorrow anyway and find out where she's dragging in the driveway (when I come in wrong). Maybe I can somehow measure how much clearance I have when I come in properly too, although that will be hard to measure very closely.

Thanks for the help.
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Old 03-20-2016, 07:59 PM   #37
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Seeeya - where did you get the round aluminum plates?

I plan to do this. I have a 6MT base 2015 WRX with the Cobb catted + resonated J/I pipes and factory mufflers. I don't want "wake the neighbors" sound level, just a little more rumble.

I'm not going to use a hole saw. I have some step drills that should work well on sheet metal - even stainless. I can probably drill the four holes faster than buying and installing the plates.

I like your idea of painting it black. I painted some aftermarket pipes on my motorcycle with high temp satin black grill paint I bought at Lowes. It is holding up well several years later (but only 6000 miles) I recommend it if you like satin / flat black.
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Old 03-20-2016, 08:30 PM   #38
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Seeeya - where did you get the round aluminum plates?

I plan to do this. I have a 6MT base 2015 WRX with the Cobb catted + resonated J/I pipes and factory mufflers. I don't want "wake the neighbors" sound level, just a little more rumble.

I'm not going to use a hole saw. I have some step drills that should work well on sheet metal - even stainless. I can probably drill the four holes faster than buying and installing the plates.

I like your idea of painting it black. I painted some aftermarket pipes on my motorcycle with high temp satin black grill paint I bought at Lowes. It is holding up well several years later (but only 6000 miles) I recommend it if you like satin / flat black.
I cut the circular covers out of aluminum stock I bought at Lowe's, with heavy duty scissors and finished them with a file.

Step drills, assuming you have ones that go to 1.5", would certainly be easier. But that SS was surprisingly tough. While the pipe inside with the plug is slightly larger, the plug is 1.5" ID inside so that's why the hole in the can is that size.

With the resonated STi center pipe and the mufflers thusly modded the car's exhaust is what I wanted. The crude raspy edge is gone, it's quieter at idle and startup, gives nice boxer sounds at low speed, and is a stealthy presence on the highway. Plus, I know now that it is free to flow the capacity of the pipes.

Thanks for that paint tip. I have some.

Last edited by SeeeeeYa; 03-20-2016 at 08:36 PM.
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Old 03-20-2016, 08:35 PM   #39
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Originally Posted by SeeeeeYa View Post
I cut the circular covers out of aluminum stock I bought at Lowe's, with heavy duty scissors and finished them with a file.

Step drills, assuming you have ones that go to 1.5", would certainly be easier. But that SS was surprisingly tough. The pipe inside with the plug is 1.5" ID so that's why the hole in the can is that size.

With the resonated STi center pipe and the mufflers thusly modded the car's exhaust is what I wanted. The crude raspy edge is gone, it's quieter at idle and startup, gives nice boxer sounds at low speed, and is a stealthy presence on the highway. Plus, I know now that it is free to flow the capacity of the pipes.

Thanks for that paint tip. I have some.
Thanks! You did a nice job cutting them out. I thought for sure they were fabricated. I have a roll of aluminum I bought to patch my roof 12 years ago. I'll go see if it is thick enough.
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Old 03-21-2016, 09:03 PM   #40
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Just added the STI Resonated mid pipe to my WRX. I too hated the startup roar in the mornings. Added a J pipe that I ordered with only a resonator..... It wasn't enough.

My wife should be happy that I don't vibrate the house when I leave the garage in the mornings.

Great addition making the car a bit stealthy!
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Old 03-21-2016, 09:23 PM   #41
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The boxer motor's signature is also now obvious without the crass influence of the OEM intermediate pipe's resonances muddying distractions.
This reads like an audiophile's wet dream.

Don't suppose you have any audio clips?
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Old 03-21-2016, 09:43 PM   #42
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An audio clip would be amazing!
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Old 03-22-2016, 07:05 PM   #43
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Does this modification with the STI or FXT mid pipe require tuning?
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Old 03-22-2016, 07:11 PM   #44
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Does this modification with the STI or FXT mid pipe require tuning?
No tune needed! :thumbup:
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Old 03-23-2016, 10:52 PM   #45
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I just sold off my N1 dual which I really liked but I knew that once I install my catted DP and intake plus some other parts sitting in boxes I would be crossing my personal threshold for the noise level. I found ablike new 15 STi resonated midpipe for $100 all wrapped up in excellent condition w may be 2k of usage. Big difference and I now know once I add dp and intake the sound will be less than my stage 1 was w N1 dual.
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Old 03-24-2016, 08:36 AM   #46
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I just sold off my N1 dual which I really liked but I knew that once I install my catted DP and intake plus some other parts sitting in boxes I would be crossing my personal threshold for the noise level. I found ablike new 15 STi resonated midpipe for $100 all wrapped up in excellent condition w may be 2k of usage. Big difference and I now know once I add dp and intake the sound will be less than my stage 1 was w N1 dual.
Now modify the mufflers. You'll have a great sound and all the flow you need.
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Old 03-24-2016, 09:28 AM   #47
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The Placebo effect is strong in this thread.

There is no way that you increased the "boxer rumble" just by modifying you muffler and mid pipe. Those have no effect on whether or not your car has a "rumble".

That "rumble" sound is due to an unequal length header on the EJ motor. The only way you're getting your FA motor to have a "rumble" would be to swap in an unequal length header, or pull a spark plug and drive like that.

As far as the performance gains, Until you remove the cats, the stock cat back is not a restriction.

Whatever performance gains you are percieving are most likey due to the change in sound, but as far as more top end highly unlikely especially since the cats are still in place.
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Old 03-24-2016, 09:08 PM   #48
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The Placebo effect is strong in this thread.

There is no way that you increased the "boxer rumble" just by modifying you muffler and mid pipe. Those have no effect on whether or not your car has a "rumble".

That "rumble" sound is due to an unequal length header on the EJ motor. The only way you're getting your FA motor to have a "rumble" would be to swap in an unequal length header, or pull a spark plug and drive like that.

As far as the performance gains, Until you remove the cats, the stock cat back is not a restriction.

Whatever performance gains you are percieving are most likey due to the change in sound, but as far as more top end highly unlikely especially since the cats are still in place.
Who said "rumble?" Not in my post. I said boxer sound... apparently you're not familiar with that.

Blah. Blah. Blah. Armchair automotive analyst ala NASIOC.
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Old 03-24-2016, 11:42 PM   #49
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I don't get why folks keep bringing the EJ up as a basis of fact for the FA motor? Catback wasn't a restriction on the EJ, that is what everyone says so it must apply to the FA as well. I don't buy that for a second. Look at the exhaust setups on both, and it starts at the HEAD.
FA - Equal length header into a twin scroll turbo to a cat then to a secondary cat, resonator then the cat back portion.
EJ - unequal length header into a Y, into the up pipe, into a standard style turbo inlet, out a down pipe, into cat, into another cat, into a resonator into catback.

Does anyone really think the exhaust velocity/volume at the end of both down pipe sections are the same? There are several different pieces of the exhaust system. Any time you make one of those pieces more efficient, the others inefficiencies become more apparent.

Now I am not going to claim that the FA catback is a huge restriction, the point I am trying to make is to not compare the EJ to the FA and act like it is apples to apples. They are two different engines, two different animals. What was necessarily true on the EJ doesn't always pertain to the FA.

SQ
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Old 03-26-2016, 10:03 AM   #50
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Who said "rumble?" Not in my post. I said boxer sound... apparently you're not familiar with that.

Blah. Blah. Blah. Armchair automotive analyst ala NASIOC.
Ok, what's the difference between your "boxer sound" and "boxer rumble"? As in the other thread. You are quick to dismiss my opinion because it does not line up with yous, but you fail to provide any tangible evidence and resort to name calling and anecdotal references.

You realize the cats are the largest restriction in the exhaust by a large margin. Anything you do after that is negligible, meaning until you remove the cats, whatever you do to the exhaust will yield you little or no gain, and in some cases, hurt performance.

But if you want to waste your time modifying a stock muffler for performance gains, you might as well clean the contact patch of your tires because the performance gains are probably very similar.
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