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Mon Dec 12, 2005
Following in the tracks of my alarm system post this evening, here is a quick post about another search engine query that brought a visitor to this site. The query was "catalytic converter removal for good". First of all, don't'. I do not know about other countries, but here in the US it is illegal to run your car on public roads without a catalytic converter, if it came equipped with one from the factory. In fact, depending on the state you live in, it may even be illegal to run your car without a catalytic converter off-road (ie, on a race track). If you are considering catalytic converter removal for off-road or track use, then I advise you to check with your state government first to see if it is legal - because it may not be.

There are 2 reasons that people usually have for wanting to remove or bypass their catalytic converter. One is failure of the existing catalytic converter. If the "guts" of the converter (it's a ceramic honeycomb-like substance) start to break up then the chunks will start to rattle and eventually clog the rest of the exhaust system. Legally, your only option is to replace the catalytic converter once this happens. Perhaps the thought of "hollowing out" the converter (removing the guts) has crossed your mind - well, be aware that it's not only illegal but it's also possible for a good, experienced mechanic to tell that it's hollow without removing it. If they notice that during inspection then you will fail (or, at least, you should fail). The other common reason for catalytic converter removal is "performance". Catalytic converters cause a little bit of restriction in the exhaust system - in general, exhaust restriction increases torque output and decreases peak horsepower output. Enough restriction, though, will decrease torque as well. Conversely, increasing the exhaust flow will generally decrease torque output at lower RPMs and increase peak horsepower output at higher RPMs. The loss of torque is usually not very noticeable at all, except in some very small engines that are already tuned for high horsepower (for example, the 1.8 liter 16 valve VW engines). The amount of extra flow that you will gain by getting rid of your catalytic converter will most likely not be noticeable - however, it can make a small difference in conjunction with other modifications such as increasing the compression ratio and installing a more aggressive camshaft (or camshafts). In general, if your exhaust system between the catalytic converter and the engine is still stock, or if your exhaust system behind the catalytic converter is stock, then you will not see any significant gains by removing your cat. You will notice a difference in the exhaust sound - that's about it. The cats used on most cars I've seen are not terribly restrictive (however, some of the older VWs like Rabbits and 8 valve Sciroccos have small cats that It's easy to see might be restrictive), and so are usually not hindering exhaust flow significantly. The most beneficial upgrades you can do to your exhaust involve the mufflers/silencers and the manifold/downpipe (or, header) - not the cat. If you install a performance header and a free flowing cat-back system and you still require less exhaust restriction, then you can go a couple of ways. If you want to stay road-legal, then you can purchase high-flow catalytic converters from companies such as Techtonics Tuning. They offer cats with full 2.5" outlets (keep in mind you will need the rest of the system behind the cat to be at least that diameter in order to benefit from it). If you are hell-bent on not having a cat at all, and if you have already checked to see whether it's legal where you live, then you can find quite a selection of headers and downpipes with longer outlet pipes that will take the place of your cat and connect directly to the mid-pipe. You can also buy "test pipes" which are just pipes with a flanged connection which will bolt in place of the cat.

So, in summary, don't be a polluter just because you think you can pick up cheap horsepower gains. If you *really* think the stock cat is holding back your horsepower output (unlikely, unless your car is either turbocharged or more than 10 years old) then save up the $150-$300 (if you own a VW) for a larger, high-flow cat so that you can increase flow and still keep the tree-hugging hippies (like me) happy. Oh, I forgot to mention one other benefit of increasing exhaust flow - it will slightly increase gas mileage. It may or may not be noticeable - depending on lots of other things.

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