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Should I Re-Fit The Cat


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#1 chris-vxt

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Posted 22 February 2020 - 02:04 PM

Hi,
I brought my 2003 VXT last year. It’s pretty standard apart from a full Milltek exhaust that’s had the section with the CAT removed so it’s currently de-CATed.

It’s going in end of March to get a new VXR turbo as the old one started smoking a little after idle and a stage 2 remap.

I’ve read a bit about getting an MOT with a de-CATed system and it seems a little unclear. Some say it’s no issue and some say you need the right garage etc.

What I’m concerned about is if I go ahead with the stage 2 map de-CATed and I get an issue come June when I’d look at the MOT would adding the CAT back on through the stage 2 map out and it’ll need setting up again or would it make zero difference? (Garage is 350 miles from home and the map it’s self is around £400 so don’t really want it done twice)

Also is the de-CAT gain worth the uncertainty each year when it comes to an MOT? I have the section with the CAT and was thinking just ask the garage to refit then the whole issue put to bed!

Any advice welcomed as to leave the CAT off or get the garage to refit. Like I say I don’t really understand the gains to be had by removing.....

Or on the flip side and I worrying about nothing and an MOT with a de-CATed system fairly normal.

Thanks!

Chris

#2 hairy

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Posted 22 February 2020 - 03:48 PM

My experience is you will need the cat to pass the MoT and the car runs fine with the stage 2 map.



#3 Ivor

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Posted 22 February 2020 - 11:00 PM

Unless you have access to a friendly mot tester it will ( should) fail the mot without a cat, at least that's my understanding, I have a removable cat that I put in for mots

#4 hairy

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Posted 22 February 2020 - 11:09 PM

Unless you have access to a friendly mot tester it will ( should) fail the mot without a cat, at least that's my understanding, I have a removable cat that I put in for mots

 

where did you get that Ivor?



#5 chris-vxt

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Posted 22 February 2020 - 11:23 PM

Thanks!

Ivor, do you notice much or a difference with the cat removed?

#6 Aerodynamic

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Posted 23 February 2020 - 11:05 AM

Cant you get a 100cel "race" cat? it wont cost you as much bhp.



#7 Ivor

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Posted 23 February 2020 - 05:28 PM


Unless you have access to a friendly mot tester it will ( should) fail the mot without a cat, at least that's my understanding, I have a removable cat that I put in for mots


where did you get that Ivor?
MMG had it made as part of the exhaust when I had stage 4 done

#8 Ivor

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Posted 23 February 2020 - 05:29 PM

Thanks!

Ivor, do you notice much or a difference with the cat removed?

Hard to say as I only put it in for the mot so always run with it out, it's mapped for it being out

Edited by Ivor, 23 February 2020 - 05:30 PM.


#9 smiley

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Posted 23 February 2020 - 09:07 PM

Cant you get a 100cel "race" cat? it wont cost you as much bhp.

 

How much would you loose with a regular cat?

I personally think it is hardly noticable.

 

I run have been running 335 bhp on the standard (300 cells iirc) turbo cat for quite a few years now.
That is on an SC car though.



#10 ayresyy

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Posted 24 February 2020 - 08:27 AM

   You can weld in V-band flanges and have a removable cat, just put in place for MOT (you definitely do need a cat if the MOT tester is doing the job properly). I just don't think the tiny power gain you may get from removing it is worth the hassle every year, plus the added strain on the turbo's oil seals.



#11 Pidgeon

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Posted 24 February 2020 - 08:33 AM

Is the OP sure he does have a CRP and not just a removed pre-cat?  As Ivor suggests, VXT CRPs require a custom exhaust, the cat is part of the pre-cat to backbox pipe which includes the flexy bit.



#12 Ivor

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Posted 24 February 2020 - 12:27 PM

You can weld in V-band flanges and have a removable cat, just put in place for MOT (you definitely do need a cat if the MOT tester is doing the job properly). I just don't think the tiny power gain you may get from removing it is worth the hassle every year, plus the added strain on the turbo's oil seals.

Removing it stops it ( the cat) getting nicked, admittedly unlikely on a VX but increasingly common on other cars, also, less likely to get contaminated and needing replacement, also flames better :)

Edited by Ivor, 24 February 2020 - 12:27 PM.


#13 ayresyy

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Posted 24 February 2020 - 12:36 PM

You can weld in V-band flanges and have a removable cat, just put in place for MOT (you definitely do need a cat if the MOT tester is doing the job properly). I just don't think the tiny power gain you may get from removing it is worth the hassle every year, plus the added strain on the turbo's oil seals.

Removing it stops it ( the cat) getting nicked, admittedly unlikely on a VX but increasingly common on other cars, also, less likely to get contaminated and needing replacement, also flames better :)

I was forgetting about the flame 🔥 side of ruining a de-cat. Worth it for that all day long!

#14 siztenboots

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Posted 24 February 2020 - 01:01 PM

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#15 chris-vxt

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Posted 24 February 2020 - 09:04 PM

Thanks for the pointers. I contacted the old owner and the main cat/ mid section was replaced with a straight through pipe.

I think I’ll replace it with a race cat. I’m no where near hardcore enough to worry about the slight restriction a race cat will generate.

Thanks for all the help, cleared a lot of it up 👍🏼

#16 FLD

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Posted 25 February 2020 - 08:52 AM

Speak to Jim at 2bular about a cat.  He sells nice quality parts.



#17 Ivor

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Posted 25 February 2020 - 12:31 PM

Thanks for the pointers. I contacted the old owner and the main cat/ mid section was replaced with a straight through pipe.

I think I’ll replace it with a race cat. I’m no where near hardcore enough to worry about the slight restriction a race cat will generate.

Thanks for all the help, cleared a lot of it up 👍🏼

Worth checking how it was done, if the straight pipe is bolted in then it should be straight forward to add a section with a cat in it instead




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