8 replies to this topic

[idlethumbs]

Morning all
I've got a new exhaust system 1.75 inch going on this weekend but I bought a decat pipe off eBay and it's a lot bigger. Probably 2.25 - 2.5 inch.
It meets ok but will this give a negative effect on the system?
Surely the point of a upgraded system is for the air to flow smoothly but where the decat meets the rear box it will be going smaller so will cause disruption??

[Guess-Works.com]

Don't bother, you'll have to fit the cat back on at MOT time, and a Decat makes negligible difference over a good condition cat.

[Swift_General]

Don't bother, you'll have to fit the cat back on at MOT time, and a Decat makes negligible difference over a good condition cat.

Re decat and having to re fit at MOT this is not necessarily to as OP does not state year of car.

The removal of a CAT in itself will only be a reason for failure if the car is subject to a full CAT test in the first place, and not all minis with CATs equipped by the factory will be subject as follows:

If it was first used from 1st August 1992 to 31st July 1995 then it will only have to pass a full CAT test if the engine is an exact match to one in a DVSA publication called 'In service exhaust emission standards for road vehicles' (18th edition). There are only 4 mini engines in there. These are:

Mini Model Code XN

1.3l Auto TBi Engine Code X Serial No 059845 onwards
1.3l Manual TBi Engine Code X Serial No 059822 onwards
1.3l TBi Engine Code Y Serial No 060488 onwards
1.3l MPi Engine Code Z

If there is a match then it will have to pass the vehicle specific CAT limits listed in said publication.

If your car does not EXACTLY MATCH any of the above then it's back to the pre CAT limits, even if your mini was first used 31st July 1995.

After that date then it's either a vehicle specific CAT test or if no match then default CAT limits apply.

Obviously if the mini is subject to a full CAT test then removal of the CAT would most likely mean the mini would fail on emmisions in any case.

If mini is pre 1st August 1992 then removal of CAT would never be an issue (I believe there were a few carb models prior to this date with CATs factory fitted).

Edited by Swift_General, 08 October 2015 - 10:32 AM.

[Guess-Works.com]

I understand all of the above... Yawn...

however, you need to change a one critical "fact" you have made...

It's not the engine number which is looked up, but the VIN of the car, the X, Y and Z mentioned relate to the 8th character of the VIN (Engine Code), and the serial is the last 6 digits of the VIN which the MOT tester will take from the car when they perform the MOT. So irrespective of the actual engine which is in the car, unless you can prove the actual engine is from an earlier vehicle, it will still be tested as requiring a CAT.

Pretty much every mini registered after 31st July 1992 will fit the criteria for CAT test in the appendix, but there may be the odd one or two which were made beforehand and not registered until later.. That's what the check is there for...

 

If you look at the OP's posts, you'll find it's a 1993 Spi, so will need to pass a CAT test, and the cat be present...

 

Luckily you have posted the numbers so I don't have to... but the OP can check his car, if the last 6 digits of the VIN are less than 059822 then he can remove the CAT without having to replace it for every MOT.

[Midas Mk1]

From actually doing it, I'd recommend a decat. 

[Swift_General]

Don't bother, you'll have to fit the cat back on at MOT time, and a Decat makes negligible difference over a good condition cat.

Re decat and having to re fit at MOT this is not necessarily to as OP does not state year of car.

The removal of a CAT in itself will only be a reason for failure if the car is subject to a full CAT test in the first place, and not all minis with CATs equipped by the factory will be subject as follows:

If it was first used from 1st August 1992 to 31st July 1995 then it will only have to pass a full CAT test if the engine is an exact match to one in a DVSA publication called 'In service exhaust emission standards for road vehicles' (18th edition). There are only 4 mini engines in there. These are:

Mini Model Code XN

1.3l Auto TBi Engine Code X Serial No 059845 onwards
1.3l Manual TBi Engine Code X Serial No 059822 onwards
1.3l TBi Engine Code Y Serial No 060488 onwards
1.3l MPi Engine Code Z

If there is a match then it will have to pass the vehicle specific CAT limits listed in said publication.

If your car does not EXACTLY MATCH any of the above then it's back to the pre CAT limits, even if your mini was first used 31st July 1995.

After that date then it's either a vehicle specific CAT test or if no match then default CAT limits apply.

Obviously if the mini is subject to a full CAT test then removal of the CAT would most likely mean the mini would fail on emmisions in any case.

If mini is pre 1st August 1992 then removal of CAT would never be an issue (I believe there were a few carb models prior to this date with CATs factory fitted).

Sorry my post bored you - I didn't find it particularly interesting either but just thought it maybe useful so someone reading who may have been under the impression that removal of a CAT means automatic MOT failure.

Edited by Swift_General, 08 October 2015 - 11:45 AM.

[gazza82]

If it had a cat originally, and doesn't now, it's likely to be a fail if the MOT computer says so ...

.

[Guess-Works.com]

If it had a cat originally, and doesn't now, it's likely to be a fail if the MOT computer says so ...

.

 

Swift' is right, there are some minis especially those carb'ed ones with the open loop catalyst can have the cat removed, and there are also some very early Single points which can also have the cat removed... but the number is limited...

The general rule is, if it has a cat, then keep it, but make sure it's in good condition... a blocked/damaged cat will do no good to your performance, and many times in the past it was a lot cheaper to remove the cat and put a decat pipe in... But since the change in the rules a couple of years ago, many vehicles which have been de-catted have had to put th cats back on, and with a new cat, there has been very little or no change in performance. I've had to put cats on two minis myself, and IMO, they actually drove better with the new cat fitted, over the decat.

[idlethumbs]

Just to clarify the cat thing. My cat is knackered and has been for the last 2 years so it failed the mot on co being too high. But both test stations due to its age just retested it as a non cat.
It then went through fine.
There are various exhaust systems out there with a downpipe designed to remove the cat so they are longer pipes. I haven't gone for one of these, I am building the system with the pipes you would buy as though keeping the cat, then removing it. This has been slightly more money, but has meant that if there is a problem in the future with an mot then I can easily fit a cat without replacing the whole system.
As I say my cats knackered anyway so although I understand a decat doesn't make much difference in power in relation to a new cat, I am expecting slightly more gain against the old rubbish one I currently have.