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      11-29-2021, 11:13 AM   #1
spdrcrgtr
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Catless vs. Catted Downpipes

Right now I have catless downpipes + single mid-pipe ... volume is a bit louder than I want and would like to reduce/eliminate the smell, but curious how the catted downpipes compare against catless from a power/hp standpoint.

I'm sure they produce less power, but how much and any noticeable spool/turbo response differences?

Has anyone tested this and will it help with smell/volume reduction?

Thanks!
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      11-29-2021, 11:40 PM   #2
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Catless downpipes with a tune usually net about 20-30 whp and 30-50 wtq. Having either your primary or secondary cats should heavily reduce the smell. I'm running catless downpipes with stock catted midpipe and I only get a gas smell when I'm idling in my garage. Should work the same vise versa. I noticed more spool sounds after switching from stock to catless downpipes but it's definitely not as much as the increase you'd get from an aftermarket intake.
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      11-30-2021, 09:07 AM   #3
spdrcrgtr
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Thanks for your feedback - Ya, i have catless downpipes, but I'm thinking about getting catted dp's, but questioning how they will affect performance.
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      11-30-2021, 09:13 AM   #4
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Quote:
Originally Posted by spdrcrgtr View Post
Thanks for your feedback - Ya, i have catless downpipes, but I'm thinking about getting catted dp's, but questioning how they will affect performance.
performance is the same with catless or high flow catted.

You'll only start seeing a difference on advanced builds pushing 600 whp+

and its only 20 whp
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      11-30-2021, 12:12 PM   #5
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Quote:
Originally Posted by spdrcrgtr View Post
Right now I have catless downpipes + single mid-pipe ... volume is a bit louder than I want and would like to reduce/eliminate the smell, but curious how the catted downpipes compare against catless from a power/hp standpoint.

I'm sure they produce less power, but how much and any noticeable spool/turbo response differences?

Has anyone tested this and will it help with smell/volume reduction?

Thanks!
I got the AA catted downpipes with GESI UHO Gen 2 cats from Mike @ x-ph over the weekend.

These are the only downpipes that don't lose horsepower when tuned as EACH cat is rated for 850 hp.
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      11-30-2021, 02:05 PM   #6
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geez there expensive ... Did you get them installed yet?
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      11-30-2021, 11:39 PM   #7
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Quote:
Originally Posted by spdrcrgtr View Post
geez there expensive ... Did you get them installed yet?
Still waiting for them to ship. I suspect it will take a few weeks to arrive
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      12-01-2021, 08:54 AM   #8
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Quote:
Originally Posted by spdrcrgtr View Post
geez there expensive ... Did you get them installed yet?
Expensive but worth it.

power, sound, no CEL. I have the AA downpipes on my G82 M4 Comp
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      12-01-2021, 09:37 AM   #9
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Quote:
Originally Posted by mike@x-ph.com View Post
Expensive but worth it.

power, sound, no CEL. I have the AA downpipes on my G82 M4 Comp
Will it pass smog with catted DP's and a single mid-pipe in California?
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      12-01-2021, 09:40 AM   #10
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Quote:
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Will it pass smog with catted DP's and a single mid-pipe in California?
Not in California
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      12-02-2021, 08:41 AM   #11
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Quote:
Originally Posted by mike@x-ph.com View Post
Not in California
F-ing CA ... do you know if it has to be fully stock to pass smog? I haven't done it in years, but I recall part of it is a visual inspection; is that what you're referring to, or is it all about the measurements coming from the exhaust?

Because with a friendly smog tech, I bet you can avoid this visual inspection.
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      12-02-2021, 08:46 AM   #12
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Quote:
Originally Posted by spdrcrgtr View Post
F-ing CA ... do you know if it has to be fully stock to pass smog? I haven't done it in years, but I recall part of it is a visual inspection; is that what you're referring to, or is it all about the measurements coming from the exhaust?

Because with a friendly smog tech, I bet you can avoid this visual inspection.
I do not know the laws there too well, but it needs to be Carb approved to pass.
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      12-02-2021, 12:47 PM   #13
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Quote:
Originally Posted by spdrcrgtr View Post
Will it pass smog with catted DP's and a single mid-pipe in California?
You will need to find a friendly smog place who doesn't care about visuals.

The car will pass as long as they don't do the visual inspection. All monitors will be ready since these are essentially EPA legal high flow cats in the remaining 49 states.
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      12-06-2021, 09:56 AM   #14
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My friend and i dynoed our cars this summer. Both run Bootmod stage 2 but my friend has the E30 map and catless downpipes. I run 20% torque reduction and stock downpipes.
On the Dynojet i got 498 whp and my friend got 514 so the difference is not big between stock downpipes and decatted which tells me that there is very little restriction in the stock downpipes considering my friend ran a E30 map too. There is even dynoruns that shows higher hp numbers with stock downpipes compared to catless ones.

Last edited by M 4 FUN; 12-06-2021 at 10:09 AM..
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      12-06-2021, 11:56 AM   #15
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Quote:
Originally Posted by M 4 FUN View Post
My friend and i dynoed our cars this summer. Both run Bootmod stage 2 but my friend has the E30 map and catless downpipes. I run 20% torque reduction and stock downpipes.
On the Dynojet i got 498 whp and my friend got 514 so the difference is not big between stock downpipes and decatted which tells me that there is very little restriction in the stock downpipes considering my friend ran a E30 map too. There is even dynoruns that shows higher hp numbers with stock downpipes compared to catless ones.
That's good to know... Thanks for the feedback
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      12-17-2021, 06:45 PM   #16
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I got catted to help pass smog
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      12-19-2021, 10:21 AM   #17
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Quote:
Originally Posted by ByByCop View Post
I got catted to help pass smog
Do you have any other mods? What state are you located in?
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      12-20-2021, 01:28 PM   #18
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I got catted to help pass smog
How often do you have to pass smog?
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      12-20-2021, 09:31 PM   #19
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Good point; i have a 2020 so mine is not for a few years at least (I think).
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      12-22-2021, 11:23 AM   #20
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Quote:
Originally Posted by Empathy View Post
Catless downpipes with a tune usually net about 20-30 whp and 30-50 wtq. Having either your primary or secondary cats should heavily reduce the smell. I'm running catless downpipes with stock catted midpipe and I only get a gas smell when I'm idling in my garage. Should work the same vise versa. I noticed more spool sounds after switching from stock to catless downpipes but it's definitely not as much as the increase you'd get from an aftermarket intake.
I for one, love the smell of a catless downpipe in the morning
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      12-22-2021, 04:39 PM   #21
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Quote:
Originally Posted by spdrcrgtr View Post
Good point; i have a 2020 so mine is not for a few years at least (I think).
DMV states;
Starting January 1, 2019, if your vehicle is less than 4 model years old, you can pay a smog abatement fee instead of getting a smog inspection for the first 8 years that your vehicle is registered.
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      12-23-2021, 10:05 PM   #22
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I'm waiting on my Remus axil back and resonated AA EL midpipe. I'm struggling between a ER catted DP and AR resonated cattless. I just want to limit the lawnmower sound of cattless but want as much power and turbo spool as possible. Would it make a difference if there is resonated DP and resonated midpipe? I've never seen anyone use it so I'm guessing it's a bad idea lol
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