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Discussion Starter · #1 ·
As the title implies, I'm trying to learn/find out about downpipes. I currently have an MBRP catback on my '16, but find that while nice when normal driving, when going wide open it's just too boomy. Now having realized this about 6 months ago, I purchased a Mountune catback which sits in it's box in the garage. Now I'm preparing to throw it on the FoST real soon, but then got to thinking. I should have ponied up the dough and purchased the catback with downpipe combo for a big discount. So I'm thinking about ordering the downpipe from Mountune. I like that that setup in that it doesn't get to crazy loud. Here is where I'm looking for advice.
I noticed there are options for catted and non-catted downpipes. What are the differences, and what is needed in order to put these in? I would tend to believe that O2 sensors are involved amongst possible other things. What I'd be interested in would be the least amount of hassle to install from the standpoint of not having to start bypassing sensors, or anything of the like. Now I know that I'll have to get a tune revision, but am I OK to go the turboback route without a FMIC upgrade? That mod will be coming next BTW.
 

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Hey man, the difference in them are pretty much in the name. One has a cat while the other one comes catless. Depending on your state and type of emissions that might help make your decision for you. But if no emission or they are not very harsh on them, catless will ususally net a few more hp, especially on BT applications while the catted version will be a bit more quite for you and help pass emissions. And for the sensors you dont have to bypass anything unless you go catless and will need a defouler that you just screw your O2 sensor into and then screw that into the downpipe. or a custom tune can help with the check engine light as well. And for your last question, as long as you get a custom tune for the dp and catback without the FMIC youll be okay. But other wise just wait till you can get the FMIC and tune it all at once.
 

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Discussion Starter · #3 ·
Thanks! Fortunately here in Michigan (at least my area) we don't have any emissions testing. If all I need is to screw in a defouler then that should be no big deal. This is good as it seems the catless Mountune is significantly cheaper.
 

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Thanks! Fortunately here in Michigan (at least my area) we don't have any emissions testing. If all I need is to screw in a defouler then that should be no big deal. This is good as it seems the catless Mountune is significantly cheaper.
Yeah man no problem, but if you choose to go catless, as long as you get the custom tune for it you don't need the defouler that screws in the pipe since the tuner will fix the issue for you through the tune itself.
 

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I would still recommend the defouler. I know a few ST owners who have had to replace their o2 sensor. It doesn't cost much to add the defouler anyways to prevent the sensor from fouling.
 

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Discussion Starter · #6 ·
I would still recommend the defouler. I know a few ST owners who have had to replace their o2 sensor. It doesn't cost much to add the defouler anyways to prevent the sensor from fouling.
I do plan to use a defouler.
 

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Discussion Starter · #11 ·
They might manufacture it themselves. Even in the video they use that generic name "Off Road Downpipe". Honestly, as long as the fitment is good, they are all the same.
After looking into them a bit more, I might just get the Depo Racing. Looks like a nice bang for the buck.
 

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https://www.amazon.com/Vibrant-11619-J-Style-Restrictor-Adjustable/dp/B00AQ7972O and use the smallest insert. I have this with a CNT catless downpipe and MBRP catback. The catless downpipe will make your exhaust louder, just a FYI since you said your previous was too loud.
Wait, I have read to use the medium insert for the vibrant defouler for our cars...Which is best, because too low can throw a code as well. I put the medium in the defouler waiting to install my downpipe until the weekend so I havent tested yet.
 

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Wait, I have read to use the medium insert for the vibrant defouler for our cars...Which is best, because too low can throw a code as well. I put the medium in the defouler waiting to install my downpipe until the weekend so I havent tested yet.
If you run a catless, you will throw a code regardless unless you tune.
 

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If you run a catless, you will throw a code regardless unless you tune.
I know that, was more curious to why he used the smallest insert rather than the medium.
 

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If you run a catless, you will throw a code regardless unless you tune.
not entirely true
I've seen many people use the non foulers (on other cars) and run catless without ever throwing a code. Inspection even shows the catalyst as ready.
 
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not entirely true
I've seen many people use the non foulers (on other cars) and run catless without ever throwing a code. Inspection even shows the catalyst as ready.
I stand corrected. Thank you! :)
 

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I had a home brew defouler on my catless and was NOT tuned... never had an issue. never threw a code. and when i put it on a tuner it showed all sensors in "Ready" state

a tune without a defouler can keep the engine code away but sensors still will not go to ready and you most likely will not pass emissions, if you do have them (i know OP doesn't but to anyone that does just get a defouler)
@davesST? i have install a Depo racing DP and it was nice, it is still in the car and the user has loads of miles on it and no complaints.
 

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Discussion Starter · #20 ·
I bought the catted version from CJPP, quality piece for sure. Honestly if you really look into them (especially catless) they all are very similar. Just have to make sure the welds look good.

BTW, I'm Detroit area too!
I'm looking at that one as well. I may go with a catted pipe to keep the boomyness down a bit, and I don't want the gas smells. I also like that it uses the stock mounting points.
 
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