Thoughts on Cat being restrictive......
Ultimate HDF Member
Joined: Feb 2010
Posts: 8,039
Likes: 1,305
From: Jayhawk Country
Remove the CAT from the stock pipe and you get the same result for a whole lot less money.
Seasoned HDF Member
Joined: Oct 2007
Posts: 56,052
Likes: 88,754
From: Western South Dakota
I don't dispute the fact that the cat is a pretty good heat source that's for sure......but I'm not sure how restrictive it is based on me putting new pipes on yesterday.
I installed Supertrapp SE's, ones designed for 10-12 bikes that have the cat in the headpipe. Straight through design with any internal blockage that you see (or can't see) in other pipes. Can see clear through to the other side.
I fired up the RK and walked behind to see how it sounded from the back. I was about 8-10 feet behind the bike and I could feel the exhaust hitting me in the shins, something I could not detect with the OEM exhaust at even a closer distance. And it was pumping out pretty good like an air hose hitting me.
I don't think that the cat is really that much of a blockage as we might think...just an observation and I certainly understand why some folks do have it removed. ...
I installed Supertrapp SE's, ones designed for 10-12 bikes that have the cat in the headpipe. Straight through design with any internal blockage that you see (or can't see) in other pipes. Can see clear through to the other side.
I fired up the RK and walked behind to see how it sounded from the back. I was about 8-10 feet behind the bike and I could feel the exhaust hitting me in the shins, something I could not detect with the OEM exhaust at even a closer distance. And it was pumping out pretty good like an air hose hitting me.
I don't think that the cat is really that much of a blockage as we might think...just an observation and I certainly understand why some folks do have it removed. ...
Leave it in, it doesn't matter to us whether you do or not..
If you're happy w/it leave it alone.
You don't need our permission..
if you want to leave it in. or buy another one w/the cat in gut out the pipe and then put it back on and then put the one with the cat back on for comparison sake.
THEN YOU WILL KNOW...
Road Master
Joined: Jun 2006
Posts: 812
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From: Jaw-Jaw (Near The BIG Chicken!)
I could and I believe it was more like 7 or 8, not 3 or 4.
Ultimate HDF Member
Joined: Jan 2009
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From: East Tn Foot of The Dragon
The cat does it's job as a catylist and heats exhaust and removes the bad stuff. This is a chemical activity and produces the heat, not the heat produced by being restricted, my 2 cents.
Thread Starter
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Road Warrior
Joined: Jul 2010
Posts: 1,816
Likes: 2
From: New Hampshire
I was just observing that since I put the Supertrapps on that the amount of "felt" exhaust while standing behind the bike has increased dramatically. In my totally unscientific observation to me the restriction seemed to more a result of the oem mufflers vs the cat
Road Warrior
Joined: Aug 2009
Posts: 1,889
Likes: 104
From: Mississippi
If it's not restrictive then why is my exhaust louder without the cat? Because, as a secondarry effect the cat breaks up and absorbs some sound waves.
If it's not restrictive then why is my exhaust cooler without the cat? Because, the cat operates on heat, It has to get hot for the catalyst material to covert harmful gases to inert gases, it captures and retains exhaust gas heat, when it's gone the heat is gone.
If it's not restrictive then why are the mufflers redesigned for the cat? Because, again the cat absorbs some sound, so the mufflers dont need to muffle as much as a non cat system.
Just look at the picture of the cat cut in half, that has to be restrictive. Yeah, look at it, closely, the total open area of the cat material mesh is more than sufficient area to support the volume of flow required by the primaries.
It's simply not restrictive.
If it's not restrictive then why is my exhaust cooler without the cat? Because, the cat operates on heat, It has to get hot for the catalyst material to covert harmful gases to inert gases, it captures and retains exhaust gas heat, when it's gone the heat is gone.
If it's not restrictive then why are the mufflers redesigned for the cat? Because, again the cat absorbs some sound, so the mufflers dont need to muffle as much as a non cat system.
Just look at the picture of the cat cut in half, that has to be restrictive. Yeah, look at it, closely, the total open area of the cat material mesh is more than sufficient area to support the volume of flow required by the primaries.
It's simply not restrictive.
Tourer
Joined: May 2009
Posts: 270
Likes: 0
From: Dunstable, MA
These are the same results seen in the automotive industry, but they still sell "Hi-Flo" Cats, wait a while Harley will start selling these "Hi-Flo" Cats for all these people that think the stock cat is restrictive and want to keep there bikes emission compliant.
Outstanding HDF Member
Joined: Sep 2007
Posts: 3,074
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From:
This debate has been going on for years on the automotive side of the fence and the cats are not as restrictive as one might think.
Fuelmoto's head pipe is not a direct comparison as its still a high performance head pipe and is not a carbon copy of the stock one. To see true comparison you'll need to run a stock head pipe vs a stock head pipe with a cat removed.
Fuelmoto's head pipe is not a direct comparison as its still a high performance head pipe and is not a carbon copy of the stock one. To see true comparison you'll need to run a stock head pipe vs a stock head pipe with a cat removed.
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Tourer
Joined: Jul 2008
Posts: 491
Likes: 1
From: Mass.
I gutted my cat and during decel you can clearly notice a HUGE reduction in the amount of backpressure ..
The shape and contour of a given mass is what would deem its amount of restriction. Just because an umbrella could be reduced to a trivial volume doesn't mean you couldn't block some wind with it ...
Last edited by Tele00; Aug 15, 2011 at 08:09 AM.
Account Retired
Joined: Oct 2009
Posts: 3,245
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From: Here
I have ran two bikes stock with the cat in and removed. My 2010 RK and my wife's 2010 SG Trike. I posted video's on how they sound with and without the cat. I could tell a little increase in power on my RK because I went to 2into1 exhaust. My wife's SG didn't add any power. In fact, she said other than a little less heat and louder exhaust, she felt like it was less power than with the cat. My final diagnosis is, the cat does not restrict flow, only add's heat!. I put her bike back stock to trade it. I've installed the Arlen ness big sucker air filter and dyna tuned Jackpot's on the 2012 Triglide we just bought. I'm leaving the cat in this one. Most of my riding is in these Tennessee mtn's. With a Captain Itch Crotch cooler, the heat from the cat is not a problem.
Picture of 2012 Triglide
Picture of 2012 Triglide