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I have the Cobb Ti catback on my19. Only put 100 miles on it though so far, but cold starts are loud. My neighbors are complaining about it when I leave at 8am. Once the system warms up, it mellows down. I'm in the SF bay area, and I haven't seen any other STI run it around here. For a catback it sounds amazing, but in Cali it might get the CHP to notice you. ($1100 ticket for modified exhaust) I will say though, It's over 95db when cold, and around 85db when warmed up. Ti takes time to warm up, so keep that in mind. It DOES HAVE LESS DRONE THAN THE STOCK EXHAUST!



Video in my post was a warm start after I already took it for a drive. You will still be noticeable when it's warmed up though.





Stock my19 STI Cobb Titanium exhaust
 

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I also had the original Tanabe full Ti medalion catback on my05. Was super loud without the suppressor for being a single exit catback.



On my07, I went with a Maddad whisper turbo-back exhaust. Catted DP with divorced wastegate. This was by far the quietest turbo-back exhaust ever. 0 drone, and it was quieter than the catback i'm running now on my19. GST in Hayward CA pro-tuned was 273whp 293wtq with a pro tune on their mustang dyno.



On my audi s4 (4.2 V8) , I had purchased a Milltek H-pipe non-res catback. It was disappointing because it was too quiet. Swapped that out for a Fast Intentions x-pipe non res and was very happy. Brought the volume up and sounded better being a x-pipe.




Maddad made the quietest tbe IMO.
 

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I think what makes a turbo back loud is because most aftermarket downpipe uses 1 cat instead of 2 cats.

I know this because when I was on stock VF48 turbo; just Corsa catback is eerily quiet inside the car until I give it full throttle - but even then it isn't loud inside the car (but what a sound).

Then I added a 3inch downpipe with a single high flow cat and that thing screams volume.

Later on I converted to VF56 twinscroll turbo and have to get HKS downpipe which has 2 cats like OEM for compliances - and suddenly the Corsa catback becomes less loud, somewhere in between stock downpipe and 3" downpipe with single cat.

The only quiet turboback exhaust I could think of is Miltek and Supersprint (they got an amazing looking manifold too!). European design for European sound, but also very European in price.

But if someone knows a good exhaust shop, maybe make a catback with Vibrant ultra quiet resonator and use something like Apexi WS2 muffler (or other similarly constructed Jazma approved muffler).
 

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I think what makes a turbo back loud is because most aftermarket catback uses 1 cat instead of 2 cats.

I know this because when I was on stock VF48 turbo; just Corsa catback is eerily quiet inside the car until I give it full throttle - but even then it isn't loud inside the car (but what a sound).

Then I added a 3inch downpipe with a single high flow cat and that thing screams volume.

Later on I converted to VF56 twinscroll turbo and have to get HKS downpipe which has 2 cats like OEM for compliances - and suddenly the Corsa catback becomes less loud, somewhere in between stock downpipe and 3" downpipe with single cat.

The only quiet turboback exhaust I could think of is Miltek and Supersprint (they got an amazing looking manifold too!). European design for European sound, but also very European in price.

But if someone knows a good exhaust shop, maybe make a catback with Vibrant ultra quiet resonator and use something like Apexi WS2 muffler (or other similarly constructed Jazma approved muffler).
Milltek is not all that quiet either, especially with ELH. The WS2 muffler is the quietest muffler period. I have heavily considered welding one in place of my Corsa bc the tone is similar, just quiter, and the Corsa is definitely one of the more tolerable exhaust out there for our cars so WS2 muffler would be just right for the daily driven 15+. I had it on my last car and loved it. It was a perfect balance. I have even gone to such great lengths to try and make Apexi build one (using my car as the test model) for a WS2 catback.
 

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Milltek is not all that quiet either, especially with ELH. The WS2 muffler is the quietest muffler period. I have heavily considered welding one in place of my Corsa bc the tone is similar, just quiter, and the Corsa is definitely one of the more tolerable exhaust out there for our cars so WS2 muffler would be just right for the daily driven 15+. I had it on my last car and loved it. It was a perfect balance. I have even gone to such great lengths to try and make Apexi build one (using my car as the test model) for a WS2 catback.
Hmmm, interesting that the Miltek isn't quiet with the ELH. Is that with non-Miltek downpipe? If you look at the Miltek full downpipe assembly it has 2 catalyst - which to me must be what made it quiet (similar to my twinscroll setup with HKS dual catalyst downpipe bolted to Corsa catback).

Well, WS2 is indeed awesome. I love it it too. In fact, all of these Jazma muffler (I called it that because back then everyone from Greddy, Apexi and Tanabe have the exact same shape muffler which are all Jazma approved) does have a great mellow tone to it. I would still add Vibrant Ultra Quiet resonator though.
 

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This is the full Miltek turboback. I am not sure if this uses single or dual high-flow cat (the Miltek downpipe is 2 pieces, so you can select to run the first half catless and the second half with cat, or whichever way you want). But I will assume this is with dual catalyst.



But I also know a 2011 STI with miltek catless (which I just remembered it actually belongs to my friend before he sold it). I think he installed Tomei EL manifold too.

Compare that to my car when it was just using Corsa catback (stock everything else inc intake).
 
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