09-04-2021, 03:19 PM | #1 |
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Downpipes Opinion Request
We all know that removing all of the cats helps the engine breathe better than catted, but if you could only do one, Primary or Secondary, which would it be and why.
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09-05-2021, 11:08 AM | #3 |
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Secondary cats because they don’t impact emissions. All emissions readings are from the primaries. If you don’t live in a emission strict state remove both but your car will smell fuel/eggs removing both.
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09-17-2021, 12:17 PM | #4 |
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If you are planning on tuning I would swap the primary and keep secondary. Removing primary will cause cel but tuner can bypass it.
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09-17-2021, 07:06 PM | #6 |
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Thanks GTATX you're catless all the way correct? I have an old 68 Chevy truck obviously no cats, it smells like fuel and etc like as you would expect from an old car. is there something about new technology that makes it smell worse than old cars, or will it smell the same more or less? from all of the complaints about it it has me confused about how bad it could be.
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09-17-2021, 07:25 PM | #7 |
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I think a lot of people complaining are not tuned for catless. I once went catless before I had a tune and the smell was terrible. With a tune, I almost never noticed it. On cold start and in heavy traffic with hot weather and no breeze it would still be noticeable but not bothersome to me. People have different tolerances.
For my F90 M5, I am inclined to go high flow primary cats and catless secondaries and leave a little power on the table. It is a comfy cruiser, winter beater, construction material and tool hauler to me, not an all out sports car though it does have very good performance for its size. Best in class, probably, which is why I bought an F90 instead of a Panamerica Turbo or RS7 or CTS-V or E63 AMG. The only other car that tempted me was a 991.2 Turbo, but it cost 50% more and was not nearly as useful. I will buy one later to complement the F90 and it may well end up catless. |
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09-17-2021, 09:19 PM | #10 | |
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Also smell is with windows down only. Cat-less also makes the car more raspier so if u like deeper rumble high flow cars might be another option. I was really looking into changes my exhaust set up from Remus catback to Akra but was told Remus is the deepest sounding exhaust for f90.
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09-18-2021, 06:52 AM | #11 |
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I'm going catless secondaries. I don't have a flash tune to code out the CEL, and I dont want any smell. Sound is not a concern for me, bump in performance and no smell/CEL are my top priorities. I'm trying to improve my 60-130 and I've reached the cars current potential at 6.71 with stock downpipes and current state of mods.
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09-18-2021, 09:01 AM | #12 |
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To piggy back on this thread, I have heard folks say that emissions only looks at primary cats and not secondary. My question is how? Emission tests the air coming out the exhaust pipe so really the cat it goes through shouldn't make a difference, would it?
In VA, we also have these automated emission testing boxes that are put on exit/on-ramp for major highways so it quite literally is just your exhaust and nothing else. |
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09-18-2021, 09:22 AM | #13 | |
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09-18-2021, 09:47 AM | #14 |
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Thanks and for in person testing, that would be an issue but in case of roadside emissions tests would it make a difference which cat the air went through before coming out the exhaust?
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09-18-2021, 09:53 AM | #15 |
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OBD2 monitoring is right after the primary cats and not influenced by the secondary cats. I don’t know the standard for sniffer tests — could be the smog station has the readings the factory would expect after the secondary cats. Or maybe it is a general standard and the additional cleanup from the secondary cats is not really needed.
Roadside van sniffer won’t be as accurate as a probe in the tailpipe so I would not worry about that if removing just one set of cats. It is more of a gross polluter thing. It won’t have accuracy or standards to distinguish your 2021 car emissions from 1995 car emissions. |
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09-18-2021, 11:07 AM | #16 |
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Primary will improve the sound and power more than secondary but are also not legal in some states.
If legal, upgrade the primaries. If not, it's not worth the hassle either get catted primary or catless secondary
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10-12-2021, 11:33 AM | #17 |
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I have a question what is legal in CT, can I use downpipes or catted downpipes or is that illegal?
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10-12-2021, 03:22 PM | #20 | |
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10-12-2021, 05:56 PM | #21 |
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Really good question. Probably getting rid of the bigger primary cat makes more power. Probably getting rid of the smaller secondary would be best for smell. If money was no object, I would buy HKS 200 cell primaries and run catless secondaries. If all out performance was the goal, I would run catless primaries and secondaries.
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10-12-2021, 06:12 PM | #22 | |
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