Hypothetically speaking, if someone removed their CAT and replaced it with a CAT housing that had the inside smashed out and replaced with a through pipe, would it pass the MOT emissions test?

The MOT tester would be fooled into thinking the vehicle had a CAT as the outside would look the same.

I seem to remeber readding that the MOT wouldnt be a problem providing the climate control was switched off (even with a Jabba remap).

This is purely hypothetical and you havent seen this, Phil (piv34uk)

Hi Phil

It is not the tester that requires being fooled but the machine.

Petrols have emmissions and diesels have smoke test.

So a diesel would get away with it but not the petrols I am afraid.

But another thing would be the lambda probe would possibly pick something up and put a warning light on the dash.

Sarah

I believe a de catted Octy did pass the emissions test...howver it matters not as it has to have a cat for the mot if it was built with one...

You could do what my old exhaust had done...that is a section of exhaust. So keep old cat ( I have mine in the shed just in case) and section of pipe...before mot, swap pipes over, after swap back.

Think before going for a decat as they are very noisey and if not right for hte car as mine wasn't very drone prone at crusing speed.

I'd love to have another, but I'd spend silly money on it to make sure it worked acoustically for what I do 90% of my driving in this car at this point. That said if I got my Navaro I'd decat it with Heinz best.

So a diesel would get away with it but not the petrols I am afraid.

Sarah

oooh.........

DaveU has a H&S decat system....very loud!!

With the rear seats removed...it's head ache inducing.....nice for playing in tunnels but not 3 hours travelling back from Jabba.

Dave even thinks it's too loud now......must be an age thing.

IIRC Jon's RS passed MOT without CAT.

So if I were to chop either side of the CAT, slide a sleeve each way on the remaining pipes, insert a section of pipe then clamp up the sleeves.

This would effectively remove the CAT and make changeover come MOT time easier.

But do you think this would be noisy if used with a standard VRS exhaust?

So if I were to chop either side of the CAT' date=' slide a sleeve each way on the remaining pipes, insert a section of pipe then clamp up the sleeves.

This would effectively remove the CAT and make changeover come MOT time easier.

But do you think this would be noisy if used with a standard VRS exhaust?[/quote']

I think it would be noiser as you've removed a sound deadening box i.e cat.....but using standard RS back box...which is big....it might not be excessively loud.

Actually thinking about this a bit more...Colin had/has a decat with a Milltek cat back and this wasn't very loud....obviously a bit more sporty but not excessive,

Having changed from the elegance to VRS exhaust yesterday I noticed a slight increase in the "sporty" sound.

Compared to the elegance exhaust which, you can't hear at all, the VRS one sounds a little more fruity.

I'm not after a big booming noise that an aftermarket system would give me, just something with a little more character.

I good example of this, for those that have heard one, is the Ford Racing Puma.

If the Octavia exhaust is like the golf then you have a cat a centre silencer and then the back box. A few golf owners replace the centre silencer with a straight through pipe for a bit more sound.

I thought about doing that while I was under the car with the angle grinder. Cutting out the CAT seemed like a good way to allow the engine to breath a little better at the same time.

Mine did indeed pass an MOT test without a CAT on emissions Marginal though.

A colleague just suggested making up a mock CAT to replace the standard part. This would be a section of pipe with a "housing" around it to look like a real CAT.

Are CAT's identified in any particular way? or would an MOT tester just look at it and assume all was OK ?

You will find that an MOT tester who is on your side could help.

But it is easy for a diesel one to get away with it.

Did you get any warning lights on with the decat?

Sarah

You'll still have to get round the fact you'll have the emmissions warning light on the dash.

Where is the sensor in the system and how does it work? Does it sense pressure before the CAT or emissions after ?

There's a lamba sensor before and after the cat. It measures the difference to make sure the cat is operating efficiently.

So assuming the one before gets a result of "dirty air" and the one after is looking for "clean air", could you just mount the second on in fresh air under the car?

I dont mean just hanging loose, but in a shield/box.

It still needs to see some exhaust gases. Some people have had success by spacing out the 2nd sensor but you have to get it just right otherwise you get a dash light and error code.

Hmmm..... I feel a trip to MKIV's and cupranet coming on

In the mean time here is a very interesting article on Lambda sensors for anyone who is interested (and has time to spare): http://www.picotech.com/auto/lambda_sensor.html

I have what you need and I bought it from a guy in the US who is a member of vortex. It definetely works with 100 CPSI cats but not sure about decats. I no longer need mine as the 2nd lambda was disabled as part of my C-C map. Unfortunately for you Stuart already has his name on it.

Thanks Eddy, a big grin spread over my face as I started to read that. Then I got to the end.....

I'll try to find his email address for you.

can you not disable or jabba disable your 2nd lambda probe as eddyh did when he got his C-C done?

I was thinking this too. Bearing in mind their close proximity I have dropped AMD an email to see if they can do it.

My old octy has a miltek on with sports cat, and was MOT'd in July. The car passed the MOT with the sports cat, but only just. The tester had to run the test nearly 10 times before he got a reading under the limit. Thats was with CC turned off, and with a cat in the system. Its still debatable if it will pass, I guess it depends on a lot of factors including how warm the engine is and maybe even the time of year.