De-catting a Xantia 90 Hdi

rory_perrett · Post by **rory_perrett** » 19 Sep 2009, 12:12

De-cat pipe for Xantia Hdi 90 bhp Ebay item 180327394533 £17.13 + £9.99 p&p.

Regards
Rory

Post by **c.morewood** » 19 Sep 2009, 12:28

Thanks Rory

John Plum · Post by **John Plum** » 01 Oct 2009, 14:58

Just got onto GSF to order a decat pipe and they informed me, categorically, they informed me that from year 2000 on it would fail an MOT if I decatted it, due to law. Are they mistaken? I'm sure you may well get away with it.. but?

John Plum · Post by **John Plum** » 01 Oct 2009, 18:19

I went back to GSF and asked Tyrone there in sales where he got his information from, and he said, that a proviso had just come in to GSF, and he cannot say how absolutley true it is in law.
I chickened out and ordered the repair pipe instead of the decat pipe. I've a fair amount to do for the MOT, see.

But if confirmed somehow, I shall get a decat for sure. My car must be like me, I like to breathe. I box is enough

MikeT · Post by **MikeT** » 01 Oct 2009, 18:27

I would like to know which law. If it's emissions, then that remains to be seen/tested. But I can well believe there being an EU law stating all models (after a certain year) must have them fitted regardless in which case, hollow it out.

John Plum · Post by **John Plum** » 01 Oct 2009, 18:34

hollow it out

Yeah!
Or, build the casing round the uncut pipe, for flow velocity.

citronut · Post by **citronut** » 01 Oct 2009, 19:22

as fare as im aware diesels are not required to have a CAT for the MOT,

the only thing is on some later cars i belive the electonics would prohibit the car being removed,

besides some GSF branch's would say that as they would rather sell you a CAT than a straight through pipe

regards malcolm

Post by **myglaren** » 01 Oct 2009, 19:42

I asked about this of my local bits and bobs supplier. He is quite a knowledgeable bloke and reckons that post 1997, if a cat is fitted as original equipment then the MOT tester will look for it and if it is net present and correct he will fail the car.

I asked with the intention of de-cating the C5. Not to be, it seems.

Probably best to enquire at the MOT testing station you expect to use.

Just had mine done or I would have asked them.

MikeT · Post by **MikeT** » 01 Oct 2009, 20:02

John Plum wrote:
hollow it out
Yeah!
Or, build the casing round the uncut pipe, for flow velocity.

Even better, I like it! 8)

John Plum · Post by **John Plum** » 01 Oct 2009, 22:02

Hi MyGlaren. I'll do to that tomorrow.

DickieG · Post by **DickieG** » 01 Oct 2009, 22:41

Re diesels, cats and MOT's, I refer you to my earlier post!!

The MOT diesel emissions test tests for smoke, whereas the catalyst removes NOX (IIRC Nitrates of Oxygen) which is not tested

John Plum · Post by **John Plum** » 01 Oct 2009, 22:50

Thanks DickieG, noted: I forgot that point, i've taken so much in in three days catching up here. I'm convinced. I don't even feel the need to speak to the MOT man, if they don't agree I'll find another.

Being spoken to by the GSF man swayed me

, especially cos I had a need to order and get some parts to get to work on it..keep momentum up.
I'll change the order tomorrow.
John

jgra1 · Post by **jgra1** » 02 Oct 2009, 09:23

1997, if a cat is fitted as original equipment then the MOT tester will look for it

My missing cat has never been called into question, to be honest I dont know how old my car is

98 or 99

Although, my mot man is a good one...

mark21td · Post by **mark21td** » 02 Oct 2009, 11:13

I removed the guts out of a cat a few years ago on a Carlton 2L i and you get a horable resanateing noise unless you can stuff a pipe inside.
Made no differance to power either, still gutless.
But diesels cycal far more air than a petrol and suffer more from restrictions so you should get an improvement in power.

John Plum · Post by **John Plum** » 02 Oct 2009, 13:04

yes exahust flow is tuned according to pipe diameter, and length. This is critical to performance, as a exhaust flow in fuel/air inlet are related through both their mass velocities as well as timing and temperature. Box resrictions are taken onto account.
If opened up it would kill performance, because flow characteristics would suffer markedly. The velocity of the exiting gases should speed up towards the tail pipe, and this achieved through length, the direction of the travel of car (assisted by wind airfolw), shape of pipe, (E.G. reverse tapers in a box ), and that includes the diameter of the pipe.

Diameter could be too large or too small, and that depends in turn on volumetric size, scavenging efficiency, inlet flow, port sizes, as well as timing and temperature.
Contact with the walls governs velocity (air into outer space quickly loses its speed, as its now undirected), so if the pipe opens out suddenly before it hits the external airstream (which assists flow), it loses velocity, and chokes the flow. Its like blocking your exhaust, or having leaks in the inlet.

A pipe can be too short even: it's a mistake to think that pipe merely slow gases down. Even the walls smoothness effects velocity, and that doesn't always mean greater smoothness is better: for inlet ports some stippling can prevent puddling of the mixture, and in the the right place can assist flow, by setting up tiny turbulances: Exhaust ports are generally best smooth, but not necessarily best straight, outer angles and internal shapes of ports into the exhaust, and into the cylinders, can also can be optimised for airflow of course

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De-catting a Xantia 90 Hdi

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