After reading many threads on here about decatting I bit the bullet and had it done.... I did not go down the route of buying a new down downpipe and had the Cat chopped and a straight through piece put in.

Doing my usually 200 mile weekend commute i tested with and without (I can share the route if anyone interested)

With cat on a steady run i used to get 50-53 MPG

Without cat on same run, time of day etc... i got 60.5 MPG

I know there are variables to the tests so are not massively accurate, but i did notice an improvement.

Just thought people may want to see my results, i will do another run this Saturday and see what i get this time

I did however notice it used more fuel going up through the gears, but once cruising it raised higher, so more ideal for high motorway miles, also felt like I lost a little torque

Edited 19 April, 201214 yr by DSS199

Additional results from this will be interesting....

It depends what condition the cat was in before it was removed.

What sort of run was it A roads, motorway, etc? Speed?

If it was on A roads at 60, then the 50-53 was low - probably caused by a partially clogged cat.

Each journey is 100 miles (ish)

Well the route is 12 miles of Country roads (very hilly and tight)

25 miles of Town roads and link roads (light traffic) (Mostly 30MPH)

62 miles of M1, M62 AND M606 (I drive average around 70MPH on motorway, reduce the speed to around 60MPH when going up an incline, and letting the car free run downhill at around 80MPH)

And by free run i don't mean being in neutral , before someone lectures me about safety, just letting gravity do the work

= 99Miles

I am also doing this southbound trip again on Saturday morning, on the exact route, so will see, obviously wind permitting we shall see the results, last weekend i had massive head wind (giggdy) so results were not brilliant around 55 MPG by memory

Edited 17 April, 201214 yr by DSS199

65.1 !!!!!!!!!!!!!!!!

Edited 23 April, 201214 yr by DSS199

Additional results from this will be interesting....

Additional results are in........

Saturday morning, same time day, same route etc, i managed 65.1 MPG on this run, another gain over my last run, also i have recently been running the car with diesel additive, Millers Eco MAX

this sounds really interesting.. im not at all in favour of cats/dpf's on diesels.. i think i might be going down this route..

have you had it 'smoketested' to see if it will pass an mot without the cat? ive seen it done on 'other' diesels and it was a stress getting them through the test..

Should be ok, have spoken to plenty of people who have had theres done, not due until febuary.

Be aware you loose a little torque

Have you seen the new MOT rules? Any car that was originaly specified with a Cat must have it in place or it is an automatic MOT failure. Think the new rules come into play on the 1st April 2012 to bring us into line with the rest of europe

Summary of the new rules here:

http://uk.autoblog.c...-are-you-ready/

Mark.

Edited 24 April, 201214 yr by MarkyTDI

http://www.motuk.co.uk/manual_710.htm

3.On vehicles that qualify for a full cat emissions test, check the presence of the catalytic converter.

For the mpg, are you going off the computer, or have you calculated it from brim filling the tank and seeing how many miles you do before brim filling it again?

I am currently doing 500 - 600 miles per week and only getting 55 mpg, so being able to get another 10 mpg would be useful.

http://www.motuk.co.uk/manual_710.htm

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Surely it wouldnt be overly difficult to stick it back in for the test? say a wk before hand to let it bed in, then take it out again after? time and effort, but once per yr... if your getting 10-20% better fuel economy its a couple of hrs a year worth spending!! ill be watching this develop, so keep us posted :-)

Well i am now considering what to do, think i will wait until MOT due in February then decide, would be interested on what other people do

Well the petrol owners (who traditionally decat for the performance benefit) have always got by with either a) knowing a friendly MOT tester or b ) swapping a cat in come MOT time.

On vehicles that qualify for a full cat emissions test, check the presence of the catalytic converter

The MOT wording is a bit ambiguous as diesels DO NOT qualify for a full emmissions test, just a smoke test (section 7.4 of the MOT manual, on compression ignition engines)

The MOT wording is a bit ambiguous as diesels DO NOT qualify for a full emmissions test, just a smoke test (section 7.4 of the MOT manual, on compression ignition engines)

thats how it is within the UK, i'm not sure how the nct (RoI equivilent) phrases it for diesels. especially now that our tax system is based on co2 emissions for anything regged after 2008. DPF's are the main reason for the surge in diesel sales here since then. (low low road tax on cars like 1.9 TDI Octy's, Mazda 6's etc... less than 200e per year!)

So im going to have to check into the emissions testing for pre 2008 diesels, as to whether it is a full test, or just smoke test like over there. if i could decat and save ANOTHER wad o cash on me fuel bill... id be a very happy camper!

65.1 !!!!!!!!!!!!!!!!

That's about what I get WITH A CAT.

Removing a new, healthy, OEM cat will give you very little. You will get a small improvement in mpg and the turbo will spool up a little quicker.

Removing a partly clogged cat can give you a big improvement as you have demonstrated. Your figures were poor, but are now OK again

That's about what I get WITH A CAT.

Removing a new, healthy, OEM cat will give you very little. You will get a small improvement in mpg and the turbo will spool up a little quicker.

Removing a partly clogged cat can give you a big improvement as you have demonstrated. Your figures were poor, but are now OK again

Agree completely, i feel i would need a re-map to get a noticable gain, may consider refitting a new cat at MOT time... IF i need to :think:

I feel and EGR valve clean would help, and i can see that my intercooler needs a clean too, summer time jobs i think

Edited 30 April, 201214 yr by DSS199

...may consider refitting a new cat at MOT time... IF i need to ...

As things stand, you don't need to have a cat on a diesel to get through the MOT. It's not even an advisory. A note to MOT testers was issued last month that clarifies this.

It's well worth cleaning the EGR, intercooler and intake manifold. You should consider doing the wheel arch vent mod at the same time. It's no substitute for a FMIC but it does help.

I think they will all be added to my to do list lol....

When i get time that is

i used to be a mot tester/test station owner.. got out of the trad bout two years ago..

i tested a few diesels that had the internals of the cat 'punched through' due to blockage etc.. they past the mot (after a long run to heat them up enough..)

perhaps rather than removing the cat, maybe just break up the cat material to de-restrict it?

mmm, tis true i do average around the 65mpg at the moment meself too. but its nice to know where to start looking when things start to drop off. I brimmed the tank with a bottle of engine wash about 3 wks ago, and on a 100mile round trip, only doing 55mph on purpose, the trip computer told me id averaged 84 to the gallon the whole trip! wish twas the case all the time...