The truth about removing cat vs. increase flow
#91
02-14-2023, 10:16 AM
Seasoned HDF Member
The sole reasons for me removing the cats are reduced heat and improved sound.....that we know may be more subjective. The reduced heat is a real measurable though. I'm not sur ehow much the extra heat affects performance. Does some of that heat travel or radiate back towards the heads? I don't know, but my leg sure does appreciate it being gone.
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#92
02-14-2023, 01:17 PM
Road Master
When we're riding, cat heat doesn't reach the engine or intake, so it doesn't affect performance. When stopped, heat radiates vertically upward, doesn't impact performance, but sure heats up your leg! I think of cat as an afterburner - it burns off anything unburned in the cylinder.
MoCo said they stuck the cats in the muffler cans to move away from rider as much as possible. Normally engine mfg's put cats as close to engine as possible to light off catalyst as soon as possible when starting. Yeah, EPA is now measuring that too - how much pollutant is exhausted before cat is hot enough to fully burn off. Getting ridiculous micromanagement.
MoCo said they stuck the cats in the muffler cans to move away from rider as much as possible. Normally engine mfg's put cats as close to engine as possible to light off catalyst as soon as possible when starting. Yeah, EPA is now measuring that too - how much pollutant is exhausted before cat is hot enough to fully burn off. Getting ridiculous micromanagement.
#93
02-15-2023, 08:28 AM
Tourer
By definition, sticking something inside a pipe will add restriction to flow. Fundamental fluid mechanics. The real question is "how much"? Modern catalyst honeycombs add very low restriction. Would be nice to see some comparative flow bench numbers, but I'm too lazy to google it at the moment.
Anyway, I bought S&S Grand National slip on exhausts with "high flow" catalysts. Which means somebody put some thought into recognizing that catalysts add flow restriction so worked on a design to minimize it. Don't know if restriction is lower than stock catalysts, don't really care that much. Just don't want to breathe a smelly motor anymore after growing up with them (leaded gas, too!).
Also btw, an earlier post stated catalysis minimize carbon output. Totally false. The amount of hydrocarbon (gasoline) put through the engine is a constant. The catalyst's platinum converts unburned HC, CO, and NOx to H2O, CO2, and N2. The amount of carbon in the exhaust remains unchanged. EPA classifies HC, CO, & NOx as hazardous pollutants. They have only recently been attacking CO2 for atmospheric warming.
Anyway, I bought S&S Grand National slip on exhausts with "high flow" catalysts. Which means somebody put some thought into recognizing that catalysts add flow restriction so worked on a design to minimize it. Don't know if restriction is lower than stock catalysts, don't really care that much. Just don't want to breathe a smelly motor anymore after growing up with them (leaded gas, too!).
Also btw, an earlier post stated catalysis minimize carbon output. Totally false. The amount of hydrocarbon (gasoline) put through the engine is a constant. The catalyst's platinum converts unburned HC, CO, and NOx to H2O, CO2, and N2. The amount of carbon in the exhaust remains unchanged. EPA classifies HC, CO, & NOx as hazardous pollutants. They have only recently been attacking CO2 for atmospheric warming.
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#94
02-15-2023, 09:15 AM
Seasoned HDF Member
2 years ago I did exactly that. There was a 105 CFM difference between cat and no cat; with the same model and year M8 head pipe, on the same day, the same flow bench, and within 5 minutes of each other. On my SG ( stock air cleaner and stock mufflers) there was little to no difference in the butt dyno and minimal increase in sound, however, I did gain about 3 MPGs from the mod (not sure why, just saying). And less felt heat. This is why I had no issues doing this to my 2022 Freewheeler over the winter. And before someone chimes in about warranty, I Don't Care, it's MY bike.
#96
02-15-2023, 09:35 AM
Seasoned HDF Member
2 years ago I did exactly that. There was a 105 CFM difference between cat and no cat; with the same model and year M8 head pipe, on the same day, the same flow bench, and within 5 minutes of each other. On my SG ( stock air cleaner and stock mufflers) there was little to no difference in the butt dyno and minimal increase in sound, however, I did gain about 3 MPGs from the mod (not sure why, just saying). And less felt heat. This is why I had no issues doing this to my 2022 Freewheeler over the winter. And before someone chimes in about warranty, I Don't Care, it's MY bike.
#97
02-15-2023, 10:08 AM
Seasoned HDF Member
just basing my thoughts on conversations with tuning professionals over time ... I personally am a bit OCD and wouldn't want to guess / hope things are just fine altering OEM parameters, rather be sure by optimization by qualified experts..that's one thing I don't mind spending money on
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#98
02-15-2023, 10:53 AM
Grand HDF Member
just basing my thoughts on conversations with tuning professionals over time ... I personally am a bit OCD and wouldn't want to guess / hope things are just fine altering OEM parameters, rather be sure by optimization by qualified experts..that's one thing I don't mind spending money on
#99
02-15-2023, 11:12 AM
Seasoned HDF Member
I yeah, my mind was just focused on retuning after cat free exhaust install on OEM tunes
#100
02-15-2023, 12:12 PM
Road Master
2 years ago I did exactly that. There was a 105 CFM difference between cat and no cat; with the same model and year M8 head pipe, on the same day, the same flow bench, and within 5 minutes of each other. On my SG ( stock air cleaner and stock mufflers) there was little to no difference in the butt dyno and minimal increase in sound, however, I did gain about 3 MPGs from the mod (not sure why, just saying). And less felt heat. This is why I had no issues doing this to my 2022 Freewheeler over the winter. And before someone chimes in about warranty, I Don't Care, it's MY bike.
Unsurprising to me, at least. Measurable flow difference, not enough to really feel the miniscule torque increase, but added some mpg and cooler leg!
Nice.