High Flow Cat Converter
I'm a big fan of catalytic converters on road cars.
Not only are they typically required by the law, they make a huge difference in the amount of tailpipe emissions. A good cat in proper working order can, from an emissions point of view, compensate for a less than perfect tune. Not only is that good for the environment, that's good for performance car enthusiasts in general. In these days of increased energy use sensibilities and "green" movements, it's only good sense to play nicely with others and not be catalogued as gross polluters doing our own thing at the expense of Mother Nature.
Majority opinion counts. If hotrodders and similar car modders are seen as the enemy of the environment, eventually the majority will pass laws that further take away our ability to keep these cars on the road and customise them as we see fit. It is a good thing to be perceived as environmentally responsible citizens.
And the easiest way to be perceived as being environmentally responsible? Be environmentally responsible.
In the mid 1970s when cats first appeared on the scene, they provided a severe exhaust restriction and murdered power. You could pick up 25% or more power by putting a "test pipe" in place of the cat. Even cats circa 1995, although much better than their 1970s ancestors, still offered a fair amount of exhaust restriction, and it is unquestionable that pulling the cat would pick up some power.
But in 2011, we have access to high-flow cats with very large cross sections on the cat substrate. These cats are every bit as effective at scrubbing exhaust of hydrocarbons and CO as the older cats, but they have next to no influence on exhaust flow (and thus power). These days, it is juvenile and irresponsible to be operating a car without a cat on the street, when these parts are so easily found and so cheap.
Plus, there's a good chance that your 100,000 km OEM cat looks like this:
So I picked up a high-flow cat from 3SX. In a happy surprise, it fit perfectly, and the only challenge in the install was breaking loose the rusted-on OEM bolts.
One caveat though - the high flow cat is much louder than the OEM cat. With tubular O2 sensor housings, a 3" downpipe, the 3" cat, and the OEM exhaust, the exhaust note is just barely on the happy side of too loud. It passes the wife test (a 4 hour trip was fine with no complaints) but any louder and it'd be pushing it. If you go with a relatively lightly muffled cat-back exhaust system, thinking that the presence of the cat will keep sound levels under control... it won't work.