Post by Sabertooth on May 8, 2020 12:19:20 GMT -5
When tuning a car with cats, you must maintain them and their operation still. That means making the same sacrifices as the factory, being that you need to lower how many degrees before TDC that the spark fires, and you need to add more fuel.
The reason for this, is that it allows more of the energy of that burning fuel to enter the exhaust pipe and flows to the cat, as well as the extra fuel reaches the cat in order to sustain the warmth and reaction. Failure to do so will result in a car that very quickly clogs the cats, as they will not get hot enough for the reaction to take place properly, so you're left with a lot of residue inside them that would normally go out the tailpipe if they were functioning (ironic)
When not plugged, the volume of the chambers where the cats are are about the same volume as the rest of the pipe, due to expanding, but being partially occupied by the cat material. Therefore, flow is very minimally affected, and scavenging can still occur. The honeycomb inside actually promotes scavenging as well and prevents turbulence due to the nature of the shape, and straight runners.
When tuning a car with no cats, or no concern over clogging them, you can pull the fueling way back and not only lower the exhaust gas temperature, but create a more full burn, where the power of the burn almost all goes to pushing the piston down and rotating the crank instead of to be used as a heat source outside the engine. That, combined with leaner fueling allows for more fuel to actually be burned in the time (the richer the ratio, the slower the flame front) that the exhaust valve is still closed, which further raises power.
So it's not that cats are an inherent restriction as many say. There was a time, but those cats were of a very different design, and you'll find them on 1970s and some 80s American cars. It's that the software compromises to run cats without ruining them is the issue. That said, a clogged cat is and will always be clogged, and should be replaced or removed as you would any other broken part
The reason for this, is that it allows more of the energy of that burning fuel to enter the exhaust pipe and flows to the cat, as well as the extra fuel reaches the cat in order to sustain the warmth and reaction. Failure to do so will result in a car that very quickly clogs the cats, as they will not get hot enough for the reaction to take place properly, so you're left with a lot of residue inside them that would normally go out the tailpipe if they were functioning (ironic)
When not plugged, the volume of the chambers where the cats are are about the same volume as the rest of the pipe, due to expanding, but being partially occupied by the cat material. Therefore, flow is very minimally affected, and scavenging can still occur. The honeycomb inside actually promotes scavenging as well and prevents turbulence due to the nature of the shape, and straight runners.
When tuning a car with no cats, or no concern over clogging them, you can pull the fueling way back and not only lower the exhaust gas temperature, but create a more full burn, where the power of the burn almost all goes to pushing the piston down and rotating the crank instead of to be used as a heat source outside the engine. That, combined with leaner fueling allows for more fuel to actually be burned in the time (the richer the ratio, the slower the flame front) that the exhaust valve is still closed, which further raises power.
So it's not that cats are an inherent restriction as many say. There was a time, but those cats were of a very different design, and you'll find them on 1970s and some 80s American cars. It's that the software compromises to run cats without ruining them is the issue. That said, a clogged cat is and will always be clogged, and should be replaced or removed as you would any other broken part
