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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Joined: May 2011
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From: Central New York
A question I have is what is the amount of air coming out of the engine vs the amount of air that the pipes, cat and muffler can flow? If the engine is pumping 14 cubic feet per minute (just a made up number) and the pipes, cat and mufflers can handle 20 cubic feet per minute then the cat is not restricting anything. Now if the engine is putting out 21 cubic feet per minute then removing the cat could allow more air to pass possibly, unless the cat itself can allow 25 cubic feet per minute, then the restriction is somewhere else.
I am not bringing heat into this comment, this is purely airflow. I have not read anything about airflow capacity for any parts of the exhaust so that is something to consider.
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From: earth
This picture shows that there is something physically in line with the flow of air so there has to be some restriction, small or large, there is a restriction.
A question I have is what is the amount of air coming out of the engine vs the amount of air that the pipes, cat and muffler can flow? If the engine is pumping 14 cubic feet per minute (just a made up number) and the pipes, cat and mufflers can handle 20 cubic feet per minute then the cat is not restricting anything. Now if the engine is putting out 21 cubic feet per minute then removing the cat could allow more air to pass possibly, unless the cat itself can allow 25 cubic feet per minute, then the restriction is somewhere else.
I am not bringing heat into this comment, this is purely airflow. I have not read anything about airflow capacity for any parts of the exhaust so that is something to consider.
A question I have is what is the amount of air coming out of the engine vs the amount of air that the pipes, cat and muffler can flow? If the engine is pumping 14 cubic feet per minute (just a made up number) and the pipes, cat and mufflers can handle 20 cubic feet per minute then the cat is not restricting anything. Now if the engine is putting out 21 cubic feet per minute then removing the cat could allow more air to pass possibly, unless the cat itself can allow 25 cubic feet per minute, then the restriction is somewhere else.
I am not bringing heat into this comment, this is purely airflow. I have not read anything about airflow capacity for any parts of the exhaust so that is something to consider.
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Joined: Apr 2007
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From: Roseville, CA
I do think some of us can tell 3-4hp difference.
Even on high-performance cars, the cats are the most restrictive part of the exhaust system.
With a stock tune, they may not flow differently. But with a tune, there will be a difference in a straight pipe vs. any kind of restriction. I would like to see the torque rating differences as well.
Even on high-performance cars, the cats are the most restrictive part of the exhaust system.
With a stock tune, they may not flow differently. But with a tune, there will be a difference in a straight pipe vs. any kind of restriction. I would like to see the torque rating differences as well.
Road Warrior
Joined: Oct 2007
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From: South Carolina
experiment. get a kid or neighbor and 20 or 30 soda straws. tape the straws in a neat bunch and shove them in their mouth...if they turn blue its restrictive, if they can breathe it isnt. If they get mad or hot, thats a by product.
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I have Stage I and Rush slip-ons on my 2010 Ultra. I'm going to remove the CAT. Dealer tells me I will need to reflash the ECM when the CAT has been removed. If the CAT is not restrictive why the the reflash?
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Do they relash it for free, or do they charge you money if they do your reflash, hmmm.
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I tend to listen to people that have spent thousands $$$ on R&D to test that theory, like Jamie at Fuelmoto over some one who "thinks" it doesn't matter. If you look at Fuelmoto's results the proof is in the pudding and I am talking about proven dyno tuned results. The convergence of exhaust gases into a cat in my opinion cannot not result in the same flow as without the cat, other wise they would put them on everything that races down at the dragstrip.
Last edited by TORQUEY; May 18, 2012 at 03:21 PM.
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Joined: Apr 2010
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From: Southern Oregon
restriction, nonrestriction set aside having that extra mass inside the headpipe to hold heat inside would be reason enough for me to get rid of it.
Heres a shot of a cat on a dyna
Heres a shot of a cat on a dyna
Last edited by ynots; May 18, 2012 at 03:36 PM.