cat by pass
- Thread starter lauris
- Start date
Guest
New member
Think you might need a "friendly" MOT station. It has been mandatory to have a cat since ???? (not sure of the year, but I am sure it was before '97).
You would have problems if you got randomly stopped and tested, and may have even more problems if caught the same way on the continent. The likihood is probably low, but the consequences may be awkward.
I wondered why by-passes were offered at all, but I believe there was a period when manufacturers fitted them before they were mandatory. Therefore for those cars, they can legitimately be removed.
I believe you may also be allowed to remove them if the car is used on track (but even track use seems to be becoming greener).
The preferred legal way to reduce back pressure and set free a few more horses is to use the race cats. They may not last as long though.
Dave Wilkinson
New member
Scott,
I suspect the magic year you are thinking about is .... 1992. The issue is not so much whether you have a cat or not ... it's more to do with whether your car can meet the emission requirements. Cars registered up to 1992 have a higher CO target than cars registered after. The cat helps achieve that lower target but it's not impossible to meet it without the cat fitted. Much will depend on the condition of the engine and the state of tune. There's no real answer other than get it tested without the cat and see. Agreed, it's not wonderfully convenient, specially if you go out and buy the cat bypass ... and then find out it won't pass!!
The race cats have fewer cells and, hence, offer less resistance to the exhaust gases but they are (a) expensive and (b) will wear out just like the standard cat. It may be the only way to go though if the bypass fails the test.
Regards
Dave
I suspect the magic year you are thinking about is .... 1992. The issue is not so much whether you have a cat or not ... it's more to do with whether your car can meet the emission requirements. Cars registered up to 1992 have a higher CO target than cars registered after. The cat helps achieve that lower target but it's not impossible to meet it without the cat fitted. Much will depend on the condition of the engine and the state of tune. There's no real answer other than get it tested without the cat and see. Agreed, it's not wonderfully convenient, specially if you go out and buy the cat bypass ... and then find out it won't pass!!
The race cats have fewer cells and, hence, offer less resistance to the exhaust gases but they are (a) expensive and (b) will wear out just like the standard cat. It may be the only way to go though if the bypass fails the test.
Regards
Dave
Dave Wilkinson
New member
Stuart,
I have to confess to having no specific knowledge of the law in this respect so I am willing to be convinced but I suspect there is a wide chasm of difference between what a manufacturer is allowed to do with a European-wide specification and what might apply to a single car in an MOT test.
I am sure that any EU specification might require things such as a cat regardless of an engine's capability to meet the emission requirement with or without since there is a need to have some confidence that the engine will remain "green" regardless of how carefully the owner might maintain it (or not). However, as far as the MOT Test is concerned, I'm pretty sure that it is only necessary to meet the emission test requirements - one way or another. If it can be done without a cat I believe that is good enough.
If someone can quote the specifics of the law which might prove me wrong I am willing to concede.
Regards
Dave
I have to confess to having no specific knowledge of the law in this respect so I am willing to be convinced but I suspect there is a wide chasm of difference between what a manufacturer is allowed to do with a European-wide specification and what might apply to a single car in an MOT test.
I am sure that any EU specification might require things such as a cat regardless of an engine's capability to meet the emission requirement with or without since there is a need to have some confidence that the engine will remain "green" regardless of how carefully the owner might maintain it (or not). However, as far as the MOT Test is concerned, I'm pretty sure that it is only necessary to meet the emission test requirements - one way or another. If it can be done without a cat I believe that is good enough.
If someone can quote the specifics of the law which might prove me wrong I am willing to concede.
Regards
Dave
38F3E1
PCGB Member
The law seems to be typically obtuse as always.
My understanding is that if a car was first used after 1st August 1994 and the exact model can be found in the DoT Emissions book or the exhaust analyser database (which a 993 would be) then the MOT tester has to perform a specific CAT test using the vehicle specific limits from the book. What they are testing for is to see if the cat has failed which is why they have to use the vehicle specific limits. Any sports cat or aftermarket cat would need to meet these limits.
I am also convinced that performing this CAT test envolves confirming the cat is actually fitted.
My understanding is that if a car was first used after 1st August 1994 and the exact model can be found in the DoT Emissions book or the exhaust analyser database (which a 993 would be) then the MOT tester has to perform a specific CAT test using the vehicle specific limits from the book. What they are testing for is to see if the cat has failed which is why they have to use the vehicle specific limits. Any sports cat or aftermarket cat would need to meet these limits.
I am also convinced that performing this CAT test envolves confirming the cat is actually fitted.
Guest
New member
Power may be increased slightly at the top end since there will be a bit less back pressure. Torque at the bottom end may be reduced slightly.
I doubt you would be looking at more than a few bhp. Whether it would noticeable is hard to say.
Removing the cat will save quite a few kilos since they aren't light.
Noise should be a little harder edged, since the gas flow will be smoothed a bit less.
It could also become more boomy in the mid range.
Sorry I can't be more specific. From the lack of people commenting, I guess not many have tried it.
Maybe the vendor could answer you questions, or are you going to weld in a bit of pipe yourself?
I doubt you would be looking at more than a few bhp. Whether it would noticeable is hard to say.
Removing the cat will save quite a few kilos since they aren't light.
Noise should be a little harder edged, since the gas flow will be smoothed a bit less.
It could also become more boomy in the mid range.
Sorry I can't be more specific. From the lack of people commenting, I guess not many have tried it.
Maybe the vendor could answer you questions, or are you going to weld in a bit of pipe yourself?
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