Tuning Cause Hotter Cat?

Reply Subscribe

Thread Tools

Search this Thread

Jan 22, 2016 | 11:24 PM

#11

harkon

Road Captain

Joined: Jul 2015

Posts: 565

Likes: 152

From: Calgary, Alberta

A number of different things are happening here. The cat basically oxidizes carbon monoxide into carbon dioxide and water. The cat must reach a certain operating temp in order to do this. In other words it gets hot. Because of this unburned fuel will oxidize (burn) in the very hot cat and create additional heat. Remove the cat and this does go away. Adding some fuel to a lean burning engine does reduce heat once the cat is removed, but that is now to correct the extreme lean condition. Long story short, get rid of the cat, add fuel to get things running properly and enjoy the ride. There is really no need to add fuel unless you increase engine flow. Open the intake and exhaust and then you need to add fuel.

You will notice an increase of volume in the exhaust note once the cat is removed. The cat offers a significant muffling effect due to its added restriction. I personally prefer what it does for the sound. Much more Harley like. Depending on the slip ons the change can be fairy profound. Again, I personally prefer it. With the cat gone and proper fuelling, you should notice the bike is less lethargic and nicer to ride. I don't need a hot rod but liked the improvement I saw. I ended up moving from a decatted stock pipe to Dresser Duals. No real change in power but the exhaust note did change for the better IMHO.

Jan 23, 2016 | 10:32 AM

#12

alarmdoug

Road Warrior

Joined: Sep 2014

Posts: 1,271

Likes: 246

From: Columbia SC

Quote:

Originally Posted by Hausguy

Just get rid of the Cat.

What he said ...

Jan 23, 2016 | 05:56 PM

#13

Hate Work

Road Warrior

Joined: May 2015

Posts: 1,718

Likes: 159

From: Maryland

As unscientific as it may be, I do not have an oil temp gauge, but have the OEM air temp gauge. Our summer here in MD. was beautiful. Range of temps was 75 to 85 most of the time.... With that said, once I installed a new header and slip-on tubes, plus did a dyno, the temperature easily went down 10+ degrees. Not only did the gauge say so, my leg said so. I kept the OEM header in case, someday, I need to reinstall due to some politician.... But otherwise, I am so glad I dropped the cake on the upgrade. Get rid of the cat.

Jan 23, 2016 | 08:32 PM

#14

Lowcountry Joe

Elite HDF Member

Joined: Sep 2007

Posts: 4,928

Likes: 69

From: Near Myrtle Beach, SC

Quote:

Originally Posted by Hausguy

Just get rid of the Cat.

Seriously. Don't understand why you would even want the damn thing in there at all. Sure, it gets hot enough to burn those pesky hydrocarbons from our very polluting motorcycles. Regardless, I will get 12 hours of sleep tonight worrying about whether or not my bike is spewing hydro carbons. I went with a completely new header and got rid of that cheap *** stock piece of crap. Some people cut the stock header open and remove the cat. Either way, I would get rid of it.

Jan 23, 2016 | 09:09 PM

#15

harleycharlie1992

Unofficial HDF Chaplain

Joined: Dec 2009

Posts: 21,149

Likes: 18,076

From: san diego

Quote:

Originally Posted by Lowcountry Joe

but what about the trees? I want to hug trees, and you guys are killing them!! How could you? Just so you bike will run cooler, run faster, last longer, and just plain be like it should? Oh the humanity!!

Jan 23, 2016 | 10:38 PM

#16

sixguns

Grand HDF Member

Joined: Nov 2013

Posts: 3,807

Likes: 1,488

From: SW Washington State

I got rid of that butt ugly purple heat trap long ago, now I have a beautiful head pipe thats actually made for motorcycles, My Harley loves me for it.

Jan 23, 2016 | 10:45 PM

#17

Bluehighways

Stellar HDF Member

Joined: Feb 2010

Posts: 3,394

Likes: 263

From: Southern California

If "Tuning" results in a Richer Mixture:

A slight increase in engine power at less than 100% Throttle will occur. This is a very large part of what most "Tuners" do.
Fuel economy will decrease a bit (you are using slightly more fuel after all).
As the efficiency of combustion decreases, (which is one of the downsides to generating more power using a richer mixture) there will be an increase in HC (Hydrocarbons, also known as un-burned fuel) and CO (Carbon Monoxide) in the exhaust.

The purpose of an Oxidizing Catalyst is to continue the burning (also know as Oxidation) of the HC not burned in the Combustion Chamber (and to continue the oxidation of the CO to result in CO2). But the point of the Catalyst is to do so at low enough temperatures (~600*F as opposed to the 2,000*F+ that exists in the Combustion Chamber) so that NOx (Nitrogen Oxides) emissions do not increase.

To answer the OPs question . . . enriching the mixture, to gain an increase in power, at the expense of efficiency, can and definitely will increase the amount of heat generated in an Oxidizing Catalyst. As the efficiency of the engine decreases, the amount of fuel (ie HC) being supplied to the Oxidizing Catalyst will increase. As a result you will get more heat from the Catalyst. Just as a campfire will get hotter the more logs you put on the fire.

Last edited by Bluehighways; Jan 23, 2016 at 10:48 PM.