no cat with stock mufflers
Elite HDF Member
Joined: Jun 2011
Posts: 3,832
Likes: 127
From: Coastal Carolina
Of course they do. But so do the exhaust gasses leaving the cylinders. (using the same tone as your post, "How do you think an internal combustion engine works?") In a scientific study of burns caused by motorcycle exhaust ("Case studies in contact burns caused by exhaust pipes of motorcycles" http://www.burnsjournal.com/article/...016-5/abstract ) they stated, "Continuous monitoring of the exhaust pipe ... on moving motorcycles showed that the temperature reached 170–250°C...".. [That’s 338-482° Fahrenheit.]
That's my point. Even with the cat removed, the exhaust is going to run 350-450 degrees. The same study showed that the hottest part of the pipe, where it exits the motor can reach 400°C or about 750° Fahrenheit. That heat, coming off the pipe near the rear jug is closest to your leg, much closer than the cat. Removing the cat does nothing about that heat.
No matter what you do, you still have your legs wrapped around an air cooled internal combustion engine. It just ain't gonna be "cool."
That's my point. Even with the cat removed, the exhaust is going to run 350-450 degrees. The same study showed that the hottest part of the pipe, where it exits the motor can reach 400°C or about 750° Fahrenheit. That heat, coming off the pipe near the rear jug is closest to your leg, much closer than the cat. Removing the cat does nothing about that heat.
No matter what you do, you still have your legs wrapped around an air cooled internal combustion engine. It just ain't gonna be "cool."
Last edited by TKDKurt; Jun 18, 2014 at 08:34 PM.
Road Master
Joined: Sep 2013
Posts: 1,185
Likes: 248
From: Sterling IL.
Think home radiators. Water temp same in pipe as radiator but without all those fins its not good at heating the room. The cat is the radiator and is releasing concentrated heat when stopped.
Elite HDF Member
Joined: Jun 2011
Posts: 3,832
Likes: 127
From: Coastal Carolina
The analogy doesn't fit. The cat is contained inside a round pipe the same as the exhaust gases throughout the system. There are no external fins to increase the surface area in contact with the external air to increase heat conduction to the outside. If the gases in the catalytic converter are reheated to 750 degrees as part of the conversion process, that heat won't be conducted to the outside any more than the 750 degree heat at where the header comes out of the cylinder. The difference is that the cat is out in the wind where the heat can dissipate. The heat off the jug is more confined and to use your word, concentrated.
Last edited by TKDKurt; Jun 18, 2014 at 08:59 PM.
Ultimate HDF Member
Joined: Jun 2010
Posts: 5,105
Likes: 16
From: Blaine, WA
Of course they do. But so do the exhaust gasses leaving the cylinders. (using the same tone as your post, "How do you think an internal combustion engine works?") In a scientific study of burns caused by motorcycle exhaust ("Case studies in contact burns caused by exhaust pipes of motorcycles" http://www.burnsjournal.com/article/...016-5/abstract ) they stated, "Continuous monitoring of the exhaust pipe ... on moving motorcycles showed that the temperature reached 170250°C...".. [Thats 338-482° Fahrenheit.]
That's my point. Even with the cat removed, the exhaust is going to run 350-450 degrees. The same study showed that the hottest part of the pipe, where it exits the motor can reach 400°C or about 750° Fahrenheit. That heat, coming off the pipe near the rear jug is closest to your leg, much closer than the cat. Removing the cat does nothing about that heat.
No matter what you do, you still have your legs wrapped around an air cooled internal combustion engine. It just ain't gonna be "cool."
That's my point. Even with the cat removed, the exhaust is going to run 350-450 degrees. The same study showed that the hottest part of the pipe, where it exits the motor can reach 400°C or about 750° Fahrenheit. That heat, coming off the pipe near the rear jug is closest to your leg, much closer than the cat. Removing the cat does nothing about that heat.
No matter what you do, you still have your legs wrapped around an air cooled internal combustion engine. It just ain't gonna be "cool."
My question is if I was to keep the stock header (I used a spare one to modify) and also keep the street cannons (which I liked the sound with the cat) and put a tune in with the power vision to suit that combo - will that cool the cat equipped stock header to a level that is tolerable?
Thread Starter
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Cruiser
Joined: May 2014
Posts: 211
Likes: 0
From: Delaware
Cats do create heat in every application. Every modern day automobile has a feature in the PCM that is called Cat overheat protection. When the Cats get to a certain temp the computer kicks in the protection mode by richening the air fuel mixture to cool the cats so they do not melt the catalytic material and clog up the exhaust. So anyone who thinks cats do not create heat is misinformed....
Intermediate
Joined: Aug 2013
Posts: 42
Likes: 0
From: Kentucky
Wow, this makes no sense. Dumping raw gas into an exhaust with a cat will cause the cat to have to "burn" all that fuel, and get even hotter. The Harley manual even mentions not driving with a mis-fire (non-ignition in the combustion chamber which dumps raw fuel out exhaust port) because it will over heat the cat.
Once again a lot of misinformation here. With a slightly richer A/F mixture the motor will run cooler and produce less heat. Everyone knows that a lean condition creates more heat in any internal combustion engine....
Road Master
Joined: Aug 2010
Posts: 1,077
Likes: 2
From: Rhode Island
Since I removed the cat from the stock head pipe there is much less heat. I'm not crazy, that is a fact & when I take my hand to the rear of the exhaust pipes exit, there is more pressure exiting from both pipes! That is a Fact! This exhaust exit pressure was less when the cat was still in the head pipe! That is a Fact! My exhaust is a tad louder because it flows better that is a Fact! The cat does restrict exhaust flow to a point! That is a Fact! My observations with cat on & removed is not rocket science here folks!
Cruiser
Joined: Jun 2012
Posts: 114
Likes: 0
From: las vegas
having a slightly richer mixture to have the engine run cooler and adding fuel to cool down the cat are 2 different things. if you add a bunch of fuel to a cat its gets HOTTER. At cold start on the vehicles i work on (MB) extra fuel is added to light the cat up quicker and bring it up to temp sooner so the car can go closed loop and the catalyst can start working.
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Elite HDF Member
Joined: Jun 2011
Posts: 3,832
Likes: 127
From: Coastal Carolina
Since I removed the cat from the stock head pipe there is much less heat. I'm not crazy, that is a fact & when I take my hand to the rear of the exhaust pipes exit, there is more pressure exiting from both pipes! That is a Fact! This exhaust exit pressure was less when the cat was still in the head pipe! That is a Fact! My exhaust is a tad louder because it flows better that is a Fact! The cat does restrict exhaust flow to a point! That is a Fact! My observations with cat on & removed is not rocket science here folks!
These are the types of unquantified testimonials you always get in these threads. You believe it did something, therefore it did.
Grand HDF Member
Joined: Nov 2012
Posts: 3,751
Likes: 459
From: Here and now
Cats do create heat in every application. Every modern day automobile has a feature in the PCM that is called Cat overheat protection. When the Cats get to a certain temp the computer kicks in the protection mode by richening the air fuel mixture to cool the cats so they do not melt the catalytic material and clog up the exhaust. So anyone who thinks cats do not create heat is misinformed....
This does not work in cars with bank fire injection as there are only two drivers in the ECM. It does work on vehicles that have with a separate driver for each injector because it can shut off one individual injector. A misfire will set a flashing check engine light which means to quit driving the vehicle ASAP.
Cats do create their own heat though. Through a chemical reaction of the exhaust gases (mainly HC and CO) running over the precious metal substrate. When you increase the HC and CO by richening the mixture the cat gets hotter. Very much like mixing a tube of JB weld together and having the mixture get hot.
Last edited by dribble; Jun 19, 2014 at 07:18 PM.