May sound a very basic thing to most but I am confused about what this actually is. As I understand it this is the prime requirement for going to Stage 2 remap and from what I gather improves the flow of the exhaust gases out of the engine/turbo.

Doing a quick bit of googling there are a variety of hits with some quite technical terminology. Some indicating it is not suitable for road use and questions over the ability of the car to pass an mot.

Can someone clear this up for me please, ideally in simple terms as I am a simple person!

The way I see it is the CAT is there to ensure the car passes emissions test that the EU require.

Removing this will give better flow and the ability for stage 2 mapping but it may not pass the emissons test @ MOT time. Most don't worry as MOT isn't due for a while but can always swap out your OEM one when needed to pass.

That is along the lines of my understanding. But how easy a job is it to swap? Is it a diy job or do you need a lift and specialist tools? Also with the cat removed some places indicate this leads to an ecu warning, possibly cleared by a remap but what happens when you put the oem part back?

I don't think this us an absolute requirement for stage 2. Large bore downpipe with high-flow sports cat should suffice. No MOT issues then.

A stage 2 remap requires a free flowing downpope. Normally uprated downpipes come with a 200 cell catalytic converter. You can also buy 100 cell downpopes which flow more again. A decat downpipe removes the catalytic converter completely. This is the most free flowing setup for an exhaust.

It will make the MOT touch and go on emissions. I've seen a fair few modified cars still pass the test with a decat in the past.

Decat exhausts make more torque and spool he turbo typically 300-500rpm earlier

If you worried about what the map will do if you swap between stock and decat downpipes get an APR map and you can switch to the stock map when ever you want

Sports cats dont last as well as oem cats some only last about a year!!

Recent changes to the mot test means its not just down to the emissions test , if your car left the factory with a cat then one must be fitted , doesnt need to be a oem cat just a cat

Mind you finding a "friendly" mot station isnt hard, I've had decats on my cars for 7 years now and not failed a test yet

As Sy says the biggest difference with a decat is the way the car drives off boost, the transition onto boost and the generally "liveliness" of the engine, often peak horsepower is not significantly affected the gains are made lower in the rpm range

Why not have a a 3" straight bore all the way and have a special MOT map by APR ?

No map can compensate for what a cat does

If it is set to run lean then surely the less fuel being burnt per each stroke produces less pollutant perhaps making it pass the test?

You said yourself, that you run decats and always passed the emissions test. Whether it was due to sheer friendliness of your tester or your motors producing pollutants below the prescribed level only you know and your tester know that.

Map will not change the chemical composition (catalyse noxious gases to less polluting ones) but will produce less of those noxious gases hopefully keeping it within the legal limits?

these engines run hot alraedy, i wouldnt want a map to be lean, that would only compound the issue, and id bet APR would refuse that option straight off.

They off to variants of stage 2 map. 200 Cell cat, and a decat(they call it test pipes).

Has anyone tested one of these with a decat? it might well pass. As said above ive seen a few cars pass with a decat downpipe.

The 'Euro 5 engines' will be coming up for the first time for a MOT emission test, so it will be interesting to see if a de-cat one meets the requirements.

The days are numbered of a station that can pull the probe out the exhaust or put it in the exhaust of another vehicle, for the test.

Simple enough for your tuner or friendly MOT station to run your de-cat vehicle for emissions pre MOT and see if all is well and it would pass.

george

If it is set to run lean then surely the less fuel being burnt per each stroke produces less pollutant perhaps making it pass the test?

You said yourself, that you run decats and always passed the emissions test. Whether it was due to sheer friendliness of your tester or your motors producing pollutants below the prescribed level only you know and your tester know that.

Map will not change the chemical composition (catalyse noxious gases to less polluting ones) but will produce less of those noxious gases hopefully keeping it within the legal limits?

All cars run pretty much the same air fuel ratio on hot idle its nothing to do with making it leaner

I said I run decats I didn't say I passed emissions test on the mot , I have a friendly mot tester who thoroughly checks the important things and is less concerned with things like emissions , you just need to use the right people

I did not mean it as a map to drive on really. Just when you arrive at the test load the special test map on, pass the test and load a "normal" one back on. I wouldn't dream about running lean AFR's on those engines. I still have my unfounded suspicions that they are being mapped to run a tad too rich and have some nasty lean spots causing misfires but that is just in my head

All cars run pretty much the same air fuel ratio on hot idle its nothing to do with making it leaner

I said I run decats I didn't say I passed emissions test on the mot , I have a friendly mot tester who thoroughly checks the important things and is less concerned with things like emissions , you just need to use the right people

So you are the ba$tard who drives me into being asthmatic!

Aren't emission tests done at certain RPMs? different for diesels and petrols? I seem to remember Lupo having the test done and being revved rather high fro my liking but may be wrong That is why I was thinking that leaning the AFR could help as it is not running on idle?

The days are numbered of a station that can pull the probe out the exhaust or put it in the exhaust of another vehicle, for the test

as far as i know, the emmision test is done via OBD on the VRS but there are some ways to cheat my dealer told me .

as far as i know, the emmision test is done via OBD on the VRS but there are some ways to cheat my dealer told me .

So you are saying it is calculated rather than measured?

The UK testing stations are still sticking things up the back end.

Annually after the first 3 years of no tests.

Unless the vehicle was built before 1960, that is.

(testers just got Equipment for checking 13 pin Electric sockets & not for 7 pin.

Our Government has not come to any agreement in going over to OBD plugging in,

Private Garages mostly as Testing Stations still in the UK & they buy their own equipment.)

There is one good thing here in that which ever Government we have, they can drag their heels for a while against the EU when it comes to Cars & stuff, they do not always 'Just Assume the Position' & brace ready for it.

Still some motoring enthusiasts in the Lords & Westminster.

Since the Pilot Schemes to look at changes on Motorbikes tests were carried out pre the 2012 changes,

ie,

Logging in at the start of the test & Webcams available over the Test Bench,

it looks like it will not be long untill Webcams are available to monitoring Testers of other vehicles 'or assist them' in matters where

an opinion might be needed.

george

Soon enough they will stick a webcam in my crapper to make sure I am not wasting water on multiple flushes ....

if it was me go fully decat but have whoever is making your exhaust allow for the cat to be bolted back in as easily as possible.

pretty much like a backbox is held on with a few bolts and a gasket.

That is the problem with catalysts, they have to reach certain temp to start the chemical processes so have to b close-ish to the engine

pretty much like a backbox is held on with a few bolts and a gasket.

Not too concerned about doing a few nuts and bolts, but more so about the ability to access them without a car lift. Would be a serious pain to have to get it removed prior to and refitted again after an mot. Would the fact that the cat looks far less worn than the rest of the exhaust not ring alarm bells at the mot?

I have the APR stage 1 map with switchability, but was wondering what people would do if not mapped by APR or Revo or anyone else who has enabled switching maps.

The UK testing stations are still sticking things up the back end.

I always thought we were getting shafted at testing stations, now you've confirmed it for me!