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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / February 2005Gutting catalytic converter
Is the gas flow through a factory converter better with, or without, the honeycomb filling? Some people say it's good to remove all or part of the insides, others say that will make the gases stall in the chamber. But some cars have an expansion chamber as a silencer anyway, don't they? > Is the gas flow through a factory converter better with, or without, the > honeycomb filling? Depends. Is the core melted or is it OK? > Some people say it's good to remove all or part of the insides Some people are idiots. > others say that will make the gases stall in the chamber. Others are idiots, too. What is it that you're trying to achieve? Low restriction exhaust systems are usually positive for economy and power. If I am correct, however, gutting the catalytic convertor can cause you issues of a legal nature. I'm not saying you will end up in prison, but it isn't the path to take. > Low restriction exhaust systems are usually positive for economy and power. Well...no. This generalized statement is flatly not accurate, because it's not nearly specific enough. This is not 1977 or 1987 we're living in, when most vehicles' factory exhaust systems were highly restrictive. Significantly changing the backpressure characteristics of the exhaust system can have significant *DOWNWARD* effects on fuel economy and driveability. > If I am correct, however, gutting the catalytic convertor can cause you > issues of a legal nature. It is a Federal crime, yes. > I'm not saying you will end up in prison, but it isn't the path to take. Right on both counts here. The correct fix for a clogged catalyst is a replacement catalyst. The correct fix for an unclogged catalyst is to leave it alone. DS Depends, can you afford the $50,000 fine? > Is the gas flow through a factory converter better with, or without, the > honeycomb filling? > > Some people say it's good to remove all or part of the insides, others say > that will make the gases stall in the chamber. But some cars have an > expansion chamber as a silencer anyway, don't they? > Depends, can you afford the $50,000 fine? I live in the UK where my vehicle doesn't legally need a converter. So, I was wondering how the gas flow through an open chamber compares with the gas flow through a chamber filled with converter filling? I know the open chamber will not be as good for gas flow as a straight pipe. Nor is a space filled with a honeycomb type filling. > I live in the UK where my vehicle doesn't legally need a converter. Wrongo, check your laws again. It's just as illegal to remove a converter on a car originally so equipped in the UK as it is in the US...and Canada...and the European Union...and Australia...and Japan. But, to answer your question: You will not gain anything by gutting the converter. > > I live in the UK where my vehicle doesn't legally need a converter. > [quoted text clipped - 4 lines] > But, to answer your question: You will not gain anything by gutting the > converter. A convertor will add some backpressure. In theory, the more back pressure you remove, the better it might be able to perform. In practise, however, the gains for this type of 'modification' are next to nothing for the ordinary driver and ordinary engine. Clearly, F1 cars do not run catalytic convertors. There is a weight penalty as well as a performance penalty. But not for us who drive the typical street 'turds'. >> But, to answer your question: You will not gain anything by gutting the >> converter. [quoted text clipped - 3 lines] > the gains for this type of 'modification' are next to nothing for the > ordinary driver and ordinary engine. If the OP is driving a 1970s vehicle then he could replace the catalyst with a modern one and get the benefit he is looking for by gutting it. If he is driving anything made within the last 15 years or so, then gutting the catalyst will likely do more harm than good unless coupled with with a bunch of other engine changes. > > I live in the UK where my vehicle doesn't legally need a converter. > [quoted text clipped - 4 lines] > But, to answer your question: You will not gain anything by gutting the > converter. A convertor will add some backpressure. In theory, the more back pressure you remove, the better it might be able to perform. In practise, however, the gains for this type of 'modification' are next to nothing for the ordinary driver and ordinary engine. Clearly, F1 cars do not run catalytic convertors. There is a weight penalty as well as a performance penalty. But not much for us who drive the typical street 'turds'. >It's just as illegal to remove a converter on a car >originally so equipped in the UK as it is in the US...and >Canada...and the European Union...and Australia...and Japan. One exception I know of is for 1975 and 1976 VW Golfs made for the US market. The rate of converter failures was so high that VW issued a TSB instructing mechanics to gut it and make some changes to the carburetor and EGR system. > >It's just as illegal to remove a converter on a car originally so > >equipped in the UK as it is in the US...and Canada...and the European [quoted text clipped - 4 lines] > instructing mechanics to gut it and make some changes to the carburetor > and EGR system. Cases like this are *exceptionally* rare, and the new configuration is put through Federal emission certification tests (multiple-day, multiple-thousand-dollar series of tests) before it's OK'd for street use. >> I live in the UK where my vehicle doesn't legally need a converter. > [quoted text clipped - 4 lines] > But, to answer your question: You will not gain anything by gutting the > converter. OK - that's what I was wondering. But - if I decide to buy a decat pipe, I think I might try gutting the converter first anyway, just to prove the point to myself. (And, I repeat that it's fine for me to do this on my particular vehicle, although generally not on others) > > But, to answer your question: You will not gain anything by gutting > > the converter. > OK - that's what I was wondering. But - if I decide to buy a decat pipe, > I think I might try gutting the converter first anyway, just to prove > the point to myself. Please keep in mind that everyone must breathe what comes out of your car's tailpipe. >>> I live in the UK where my vehicle doesn't legally need a converter. >> [quoted text clipped - 10 lines] > (And, I repeat that it's fine for me to do this on my particular vehicle, > although generally not on others) There's another problem in removing the catcon - the thing generates some backpressure, and the replacement pipe won't so you may have some driveability issues. > There's another problem in removing the catcon - the thing generates > some backpressure, and the replacement pipe won't so you may have some > driveability issues. A lot of people don't understand this. They think, incorrectly, that ANY amount of backpressure is necessarily a bad thing, and that ANY reduction in backpressure will necessarily improve (pick one or more) performance, economy, driveability, their sex life. Is that the very same UK that is always bitching about how short (<15-20km) oil change intervals in the US are screwing up the ecology? Inquiring minds, and all that, you know...... | > Depends, can you afford the $50,000 fine? | [quoted text clipped - 4 lines] | I know the open chamber will not be as good for gas flow as a straight pipe. | Nor is a space filled with a honeycomb type filling. > Is that the very same UK that is always bitching about how short > (<15-20km) oil change intervals in the US are screwing up the ecology? The very same UK. They also jumped halfassedly and belatedly onto the emission control bandwagon, requiring catalytic converters on all new cars in *1991* and _mostly_ taking leaded auto fuel off the market in 2000. Oh, and publishing all kinds of propaganda about how diesels are far cleaner and their exhaust less deleterious to health, and taxing their fuels to match this propaganda, until it was discovered (Whoops!) that they were wrong. When that discovery was made, they carried on as though nothing had happened, still babbling about how much cleaner/safer/better diesels are... Anyone who's been a pedestrian in London vs. New York knows they're full of sh.t. > > Is that the very same UK that is always bitching about how short > > (<15-20km) oil change intervals in the US are screwing up the ecology? [quoted text clipped - 11 lines] > Anyone who's been a pedestrian in London vs. New York knows they're full > of sh.t. Well, actually the thing is that there's fewer cars and car owners in London than in New York, so it kind of evens out. Ted |
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