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Discussion Starter · #1 ·
With the stock catback?


Mods currently are intercooler, aem dryflow filter, and tune. I love how quiet the car is so I don't want to make it too much louder, thus I don't want an aftermarket catback. If I bought a depo catted downpipe and used it with the stock catback, would I notice any performance increase (once I get a retune)?


I drove my cousin's st with a full exhaust and it pulls SO much harder in the top end than my car. He has catless though, and full exhaust.
 

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With the stock catback?


Mods currently are intercooler, aem dryflow filter, and tune. I love how quiet the car is so I don't want to make it too much louder, thus I don't want an aftermarket catback. If I bought a depo catted downpipe and used it with the stock catback, would I notice any performance increase (once I get a retune)?


I drove my cousin's st with a full exhaust and it pulls SO much harder in the top end than my car. He has catless though, and full exhaust.
Downpipe is one of the better bolt ons for these cars. The stock catback (from what I’ve heard) is good for more hp than the stock turbo can put out so you won’t need a catback unless you go big turbo. But even with a catted downpipe, you’ll get more out of it then the stock one.


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Man I honestly dont think its worth the money or the time to change out the downpipe unless you are going catless. Just my opinion though.
 

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Gains would be minimal at best with the catted downpipe and the install is not fun. Might as well go catless and make it worth it. It probably wont be much louder with the stock catback anyway just will gurgle more and be a deeper tone.

To answer your question though you would probably feel a little difference with the catted downpipe.
 

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Even catted the difference is noticable on a stock tune. Tested this with a friend's 15 ST. Now that he is tuned he loves it even more. He has the stock exhaust with no resonator. That bend in the OEM dp is garbage
 

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I'm running a Mountune catback (which is a 2.5") with a CJ PonyParts catted DP. I definitely feel more push with the new DP. I only went catted, because I know the Mrs. would gripe about the little bit of non-catted exhaust odor. I didn't find DP the install to be nearly as daunting as others reported.
 

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I saw a bump in power with my catted Depo Racing 3" DP, but I get a CEL on nearly everytime I drive it now. I did a KAM reset. She definitely pulls much harder now, but I also had the resonator deleted and went with all 3" pipe back to the stock muffler. I'm just bummed Torrie at Unleashed refuses to help me by turning off the CEL for P0420. He says its illegal for him to turn it off...lol, I bought a catted 100 cell DP to keep it legal, it is legal. So bummed now...
Are you running defoulers for the O2 sensors?
 

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I am in stock catback with mountune high flow cat. Have recorded an 8 whp gain adding the catted DP on dynojet. The car definetly feels quicker, pull harder, better throttle response. Catted vs Catteless IMO would be 1-2whp difference on our ko3 unit.
 
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Keep in mind that there are benefits, beyond HP, you'll get by freeing up exhaust flow. The turbine wheel is going to spool faster and decelerate slower. They are mild benefits, but honestly, I think you'll notice that more than the 4-5 horsepower.

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Catless all the way! Run a defouler and just build / buy a quiet exhaust or keep stock exhaust.

If you do a proper smog test in your county then just go catted with a defouler.
 

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With the stock catback?


Mods currently are intercooler, aem dryflow filter, and tune. I love how quiet the car is so I don't want to make it too much louder, thus I don't want an aftermarket catback. If I bought a depo catted downpipe and used it with the stock catback, would I notice any performance increase (once I get a retune)?


I drove my cousin's st with a full exhaust and it pulls SO much harder in the top end than my car. He has catless though, and full exhaust.
OP, I'm running a catted DP from CJ Pony Parts and DynoJet showed a gain of about 20 hp & 30 tq. I went with the catted because IMHO I think the sound with my catback is perfect. I didn't like the catless sound.

Either way, you'll gain. If you don't need emissions testing, catless is cheaper as well lol.
 

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Discussion Starter · #15 ·
OP, I'm running a catted DP from CJ Pony Parts and DynoJet showed a gain of about 20 hp & 30 tq. I went with the catted because IMHO I think the sound with my catback is perfect. I didn't like the catless sound.

Either way, you'll gain. If you don't need emissions testing, catless is cheaper as well lol.

That much gain? Was that after a tune or on stock?

A friend of mine who has a 2017 ST with stock tune has intercooler, catless DP, and cobb catback. On my car I only have IC and tune (stock exhaust). I barely beat him. So I don't know if I would have beat him a lot more if he was completely stock or if the DP really made a difference on his car.
 

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That much gain? Was that after a tune or on stock?

A friend of mine who has a 2017 ST with stock tune has intercooler, catless DP, and cobb catback. On my car I only have IC and tune (stock exhaust). I barely beat him. So I don't know if I would have beat him a lot more if he was completely stock or if the DP really made a difference on his car.
Tune makes a HUGE difference as well as weight and other stuff. Depending on the tune you and him use that's probably why
 

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That much gain? Was that after a tune or on stock?

A friend of mine who has a 2017 ST with stock tune has intercooler, catless DP, and cobb catback. On my car I only have IC and tune (stock exhaust). I barely beat him. So I don't know if I would have beat him a lot more if he was completely stock or if the DP really made a difference on his car.
Just as @brian60 said, a tune is how you actually realize all your bolt-ons.
 

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OP, I'm running a catted DP from CJ Pony Parts and DynoJet showed a gain of about 20 hp & 30 tq. I went with the catted because IMHO I think the sound with my catback is perfect. I didn't like the catless sound.

Either way, you'll gain. If you don't need emissions testing, catless is cheaper as well lol.
that power and torque didnt come from the downpipe...from the tune AND mods, yes, but def not just the DP.

To chime in - i went from Stage 2 w/ Cobb tune to Stage 3 Cobb tune to Stratifed tune and there was minimal difference between 2->3 other than quicker spool and greater response from acceleration, but exhaust did sound better. The stratifed tune cleaned up what the COBB tune was lacking and after the Datalog Refinement she is smooth as butter across the power band
 
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