I didn't have a touring bike head pipe available today...But I shot the inside of a 2012 Dyna muffler with a cat...I can't see where this can't be somewhat restrictive.
Thoughts on Cat being restrictive......
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Real easy, because there is more "open" area in the mesh cross secton profile of the catalyst, than the combined cross section area of the two primaries that feed into it. There would have to be less cross sectional area down stream from the primaries for a "restrictive" condition to exist, and that simply isn't the case, it's an illusion.
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One final effort. As one poster has it right there is more open area in the cat than the area of the two head pipes.
To the poster that said cat heat up from being restrictive. That is total BS. Cats heat up because the chemical action and only do their job when they reach operating temperature. They react to the gases passing through them and the process generates heat.
I have gutted my 10 Dyna Super Glide, 10 Ultra and 12 Road Glide. All sound the same as before and none gained any performance as there was no reduction in back pressure. The back pressure is from the stock muffler and not the cat. I do not buy less restrictive exhaust which would gain performance as I use that money to add bikes every year. 2013 Softail Slim here we come!
I only gut the cat to keep the pipes behind it and the front of the muffler from turning gold then blue. I hate blue pipes.
To the poster that said cat heat up from being restrictive. That is total BS. Cats heat up because the chemical action and only do their job when they reach operating temperature. They react to the gases passing through them and the process generates heat.
I have gutted my 10 Dyna Super Glide, 10 Ultra and 12 Road Glide. All sound the same as before and none gained any performance as there was no reduction in back pressure. The back pressure is from the stock muffler and not the cat. I do not buy less restrictive exhaust which would gain performance as I use that money to add bikes every year. 2013 Softail Slim here we come!
I only gut the cat to keep the pipes behind it and the front of the muffler from turning gold then blue. I hate blue pipes.
Last edited by lh4x4; May 2, 2012 at 09:48 PM.
From what I have seen and read about the cats I think I can understand why there might be a noticeable change in sound while not really affecting the volume or back-pressure. I don't think I am too concerned about it on my bike though. 
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No, not really, I never spent much energy pondering why race cars don't add heavy, non-essential components when they aren't required by the rules. I wonder why they don't use air conditioners, they're fantastic.
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The EPA needs to disappear, but there is not a politician out there that has the huevos to put that on the table. The damage has been done and will likely never be undone. The most we can hope for is a modest downsize and get them somewhat reigned in. The EPA is a trainload of bureaucrats that have to justify their salary......sooooo, they screw with almost everybody. Results.......they don't need no stinkin' results!