Best type of Cat?
- Thread starter LukeZ
- Start date
- Status
I took in my old 1994 4.0 jeep that had 18 month oil in it, 5 month old gas and drove 10 minutes in the city to the test facility and it passed first shot
I thought you were suggesting a dual exhaust setup with the 2 cats. Even a stock split exhaust with two cats would still fail visual check as inspectors can view the exhaust system on a video monitor. The government doesn't want people to tamper with the cat converter, if the car came with a single cat from the factory, you are legally stuck with a single cat setup. Not sure about other states, but the first step in a NJ inspection is a visual check of the exhaust via a in floor camera with bright leds and monitor.
More on topic for the op, there really isn't such a thing as a high flow or high performance cat converter, anybody that says so isn't being truthful. A converter has no moving parts, packing, or chambered like a muffler, all they do is reduce harmful gasses in the exhaust. None are designed to move gasses more quickly including spiral core. It is just a gimmick to get people to pay double for a regular converter, don't fall for it.
Now some aftermarket converters do flow more than OEM, because they have fewer cells so they clean the exhaust less well and have shorter lives. OEM converters are built to last 80,000 miles while most aftermarket converters only have a 25,000 mile life.
Last edited:
You're wrong again, some areas forced race cars to install cats and the spun cat was developed so there is very little restriction in the exhaust. I doubt you will believe that but I'm not interested in conversing with you. The op asked for suggestions on cats but your took it upon yourself to point out the laws. The laws that have been posted in other threads that were relevant to that discussion.
Sorry if i have caused any issues with the dual exhaust snipit but luke if i were you i would look in to a highflow cat or even look at the laws and see if you can install dual exhaust you would love the sound
There are a lot of factors that go into the efficiency of the converter, but I'll make it simple. We'll discuss this hypothetically first, to isolate the results from changing only the substrate. If you compare two converters of very similar dimensions and physical shapes on the same engine,
1. the metallic substrate cat may be marginally more efficient at idle for HC, CO, and NOx, at least on paper. But exhaust temperatures, idle AFR, and a lot of different factors really come into play here.
2. the ceramic substrate cat will be more efficient at HC and CO conversion for lower to medium loads and rpm ranges. These are the kind of conditions you may have on an emissions dyno test.
3. the metallic substrate will convert HC and CO better under higher loads and rpms, but these are not likely to be tested at an emissions station.
4. NOx numbers probably won't change much between either type of converter, except perhaps at idle.
Now that's examining the substrate material only. The fact of the matter is, physically smaller converters with less volume will not burn as clean. Conversion efficiency is measured by comparing how much gas is converted vs the amount of exhaust gas per a unit of volume in the cat. This is what's called space velocity:
Space velocity = a constant * [exhaust gas flow / (exhaust molecular weight * catalytic converter volume)]
In conclusion, for aftermarket performance applications a metallic substrate converter will yield at least some improvement in performance compared to a ceramic substrate cat of similar dimensions. This improvement can't be easily quantified because it depends on a number of factors. On OBD 1 cars that need sniffer tests, it may be more difficult to pass with a metallic cat. This is especially true with performance cats because they are physically a lot smaller (less volume) than OEM units and thus don't work as well to clean up the exhaust. On OBD 2 cars where no actual sniffer tests are involved, just plugging into the OBD2 ALDL, there really isn't a downside to using a high quality metallic substrate cat if you are a performance enthusiast.
So when asking about performance, are you talking about exhaust flow though a converter or how well a converter performs at converting harmful exhaust gasses? A lower cell count converter may flow a tiny bit more at the expense of pumping out a lot more emissions. It is very much a having your cake and eating it too type situation. Stockers have 700 cells per square inch while aftermarket units are around 200 cells per square inch. About the only measure of how well a cat will do its job of cleaning your exhaust is cost. Cheap ones have fewer precious metals to clean up your exhaust, expensive ones have more precious metals. Spiral cores only flow marginally better and maybe worth 1 HP. There really isn't such a thing as a high flow or high performance cat, just a gimick to con more money out of gearheads. Basically you are paying more for a lower cell count cat that will do its job worse than stock. Similar to a higher flowing air filter which flows more by filtering less.
1. the metallic substrate cat may be marginally more efficient at idle for HC, CO, and NOx, at least on paper. But exhaust temperatures, idle AFR, and a lot of different factors really come into play here.
2. the ceramic substrate cat will be more efficient at HC and CO conversion for lower to medium loads and rpm ranges. These are the kind of conditions you may have on an emissions dyno test.
3. the metallic substrate will convert HC and CO better under higher loads and rpms, but these are not likely to be tested at an emissions station.
4. NOx numbers probably won't change much between either type of converter, except perhaps at idle.
Now that's examining the substrate material only. The fact of the matter is, physically smaller converters with less volume will not burn as clean. Conversion efficiency is measured by comparing how much gas is converted vs the amount of exhaust gas per a unit of volume in the cat. This is what's called space velocity:
Space velocity = a constant * [exhaust gas flow / (exhaust molecular weight * catalytic converter volume)]
In conclusion, for aftermarket performance applications a metallic substrate converter will yield at least some improvement in performance compared to a ceramic substrate cat of similar dimensions. This improvement can't be easily quantified because it depends on a number of factors. On OBD 1 cars that need sniffer tests, it may be more difficult to pass with a metallic cat. This is especially true with performance cats because they are physically a lot smaller (less volume) than OEM units and thus don't work as well to clean up the exhaust. On OBD 2 cars where no actual sniffer tests are involved, just plugging into the OBD2 ALDL, there really isn't a downside to using a high quality metallic substrate cat if you are a performance enthusiast.
So when asking about performance, are you talking about exhaust flow though a converter or how well a converter performs at converting harmful exhaust gasses? A lower cell count converter may flow a tiny bit more at the expense of pumping out a lot more emissions. It is very much a having your cake and eating it too type situation. Stockers have 700 cells per square inch while aftermarket units are around 200 cells per square inch. About the only measure of how well a cat will do its job of cleaning your exhaust is cost. Cheap ones have fewer precious metals to clean up your exhaust, expensive ones have more precious metals. Spiral cores only flow marginally better and maybe worth 1 HP. There really isn't such a thing as a high flow or high performance cat, just a gimick to con more money out of gearheads. Basically you are paying more for a lower cell count cat that will do its job worse than stock. Similar to a higher flowing air filter which flows more by filtering less.
Good thing he didn't ask what time it is, We would have gotten a tutorial on how to build a clock. ;-)
- Status
Similar threads
