Cars registered before 1st August 1992 (i.e. J prefixes and earlier) do not require catalytic converters to pass the test. Some manufacturers fitted catalytic converters to cars built before 1st August 1992, only these can be legally removed. The MOT station will then apply the non catalytic converter test to the car.
To summarize, cars registered after 1st August 1992 require catalytic converters, and those registered before do not. Although removing a catalytic converter from a car registered after 1st August 1992 is illegal, it would only be detected during an MOT. Obviously I can't endorse illegal activity therefore you will just have to read between the lines. Please check the legality of removing the catalytic converter in your county.
This is what I believed to be true. However having spoken to Tanc Barrett they say it's not as clear cut as this. As the law stands in the UK it is the engine and not the car that does or does not require a catalytic converter to be fitted/tested. For example, if you fit a 1991 engine in a car built in 1999 and have some kind of proof of the engine type (an old log book say) then the tester would be obliged to carry out a pre catalytic converter test.
Okay, so there are potential legal problems but what do I actually achieve by replaceing the catalytic converter with a straight through pipe? The exhaust will sound considerably louder with quite a fruity rumbly sound compared to with the rather whiney sound with the catalytic converter fitted. You should find that the power delivery will be much more linear and stronger below 4000 rpm.
Nareman Virk removed his catalytic converter. The replacement pipe was specially made up by a company that custom builds exhausts. It was originally made as a simple straight through pipe, but was extremely 'boomy' and so he later had a silencer fitted. Nareman gave them the original cat upon which they based the replacement pipe, but he says that it was well worth the effort as it gave a dramatic improvement in mid-range performance. Narman had his made of stainless steel, so that it won't corrode, but it does mean you get a rather tinny resonating sound coming from the pipe at high rpm. He is going to have another made up in mild steel to overcome this problem. The pipe for a 5 door version has aflange on one end and a sleeve on the other where as a 3 door version is flanged at both ends.
Calvin Jones had a replacement made in UK by BTB exhausts (01327-261797). They will fabricate one which is essentially a straight through pipe with no baffles and will lighten your wallet to the tune of £111.63. It fits very easily and is very well made. Like Nareman, Calvin found the boom unbearable on long journeys.
Rogerio Ferrari removed his catalytic converter and says it's a little bit loud but the result in low end power is worth it.
Ben Sleeman has replaced his catalytic converter with a 2 inch stainless steel straight through pipe which was custom built. The improvement is very clear, the thing just moves like shit of a shovel in the low rev range.
I understand that pre 1993 catalytic converter replacments are no longer
made by Supersprint.
Calvin Jones has the Bosal system fitted to his car from the catalytic converter back. The two piece system only costs £119.85 and seems quite good quality with a nice chrome tailpiece.
has a Remus exhaust system. The
complete exhaust (which consists of two parts fitted just behind
the catalytic converter) costs approximately 450 Euros. Karim knows
someone who works at the Remus factory so he got the exhaust cheaper
than the normal retail price. Remus is an Austrian company situated
in Bärnbach. The owner of Remus used
to work for Sebring, and now he's in a position to
make Sebring a subsidiary of Remus!
Anyway the exhaust looks and sounds great and fits perfectly
, no bending, welding or swearing necessary! The tailpipe measures
92mm × 78mm. The original part numbers are as follows:
Middle section: 110
Rear section: 90
Nareman Virk also has a full Remus exhaust system. It cost £370 for the full system which comes all in one piece. Fitting was fairly easy, but he got a friend to do it for him. He jacked the back of the car up and changed it himself on his drive, all in under an hour.
Alex Wakefield also has a full Remus exhaust system. He swears the car just flies now. No hesitation, no flatspots, the way the car goes up to and beyond 100mph is like nothing I ever experienced before in his car. The most amazing thing is that you don't need to rev the nuts off the car to do this, it's like someone put another engine in the back!
Markus Hasse has an exhaust made by "CSC" in Italy. It's cheaper than the Supersprint system and is the only system he found that gave him a bit more power. The exhaust does not have a middle silencer only a rear. It's a bit louder, but you can feel the difference.
fitted a new 'powerflow' stainless steel exhaust
system costing £235. The difference is very noticable,
although fuel consumption has suffered slightly. The exhaust
is custom made on the car and removes the catalytic converter.
The sound is deep and rumbly but not too boy racer!
I say removing the catalytic converter does not effect the readings
from the Lamda sensor at all. It's fitted upstream of the catalytic
converter and so the oxygen content of the exhaust that it picks up
is the same.
Nareman Virk says that
he thinks that removing the catalytic converter does shorten the life of
the standard exhaust. While he had his Remus exhaust removed from his car,
he had to buy a new standard Fiat exhaust that only lasted 6 months
before the middle section started blowing. Of course, this may just
be a one off poor quality exhaust, but removing the catalytic converter
does put more pressure on the middle and back section of the exhaust.
He doesn't think the K+N would affect it, and doesn't know about the chip.