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Catalytic converter

8K views 7 replies 6 participants last post by  Rob446 
#1 ·
I’ve been informed there is no high flow cats for my 2015 SXT 3.6 so I was gonna remove them and then gut the cat for more flow any suggestions for preventing the engine light from coming on?


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#2 ·
Don't know what state you are in, but you might find this site of some value:


https://www.semasan.com/resources/exhaust-noise-laws-state


It is in violation of federal law to modify a car's emissions hardware.


This includes "gutting the cats" and the subsequent modification to the car's engine controller to force it to ignore the now no functioning post converter O2 sensor signals.


It is unlikely the factory converters are in any way restricting exhaust flow. All you will likely do is turn a perfectly fine running vehicle into a foul smelling, gross polluting piece of crap running car.


If you really feel the factory exhaust is sub par, best advice I can offer is research aftermarket exhaust systems that (at least) claim to offer better performance, probably more noise, and should in some way still adhere to the emissions laws so you are not violating the law when you install the exhaust system.


Keep the factory exhaust system in case the aftermarket one drones, or in some other way proves to be less that satisfactory, so at least you can return the car to what it was before.
 
#4 ·
Don't do it. Any gains that might be had (and there are probably none) will be too small to be felt in the driver's seat.

Totally not worth it IMO.
 
#5 ·
Yeah as everyone has already said, it won’t help very much.
It’s also illegal federally but you and everyone else probably know that already.
Sound gain will be minimal and exhaust flow gain will be virtually nonexistent.


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#6 ·
I recently installed SW downpipes in place of the stock pipes with catalytic converters. In addition to the removal of the cats, the SW pipes are 3" dia. to the connection with the stock exhaust pipes where the original down pipes are 2.5". I took a significant amount of time to fit the reducers in a manner that the catless pipes could be removed and cats reinstalled easily. I plan to use the SW pipes in spring and fall when racing and use the stock pipes when not racing. Bung extensions were used to keep O2 sensors out of the exhaust flow. No tuning changes were made and no MIL codes have displayed.

The noise level has increased however it is still quieter than most aftermarket cat back systems. Running in default mode it is only slightly louder than before, the sound system and conversations are only minimally affected. As well there is a drone when under heavy load at low rpm. At WOT it is noticeably louder than stock. The smell of gas is evident when the car is started in the garage and is occasionally noticeable at other times.

Two tuners I communicated with indicated the mod would be worth approximately .1 ET improvement. While my PB has not improved to date, I have equalled the PB and am hitting within .005 of my PB on a regular basis in DA of 1000' to 1500' greater. Since installing the pipes I am experiencing tire spin on almost every run, even on a well prepped track. No question I will need a lower tire pressure than before. On street tires it is much easier to unintentionally spin tires. Don't know if my experience is typical or not but I have definitely experienced a very noticeable performance gain.


OK I'm a bad boy for removing the cats but the car gets limited highway use, is not a DD, and cats will go back on when spring racing is done.
 
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