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-   -   Which cat should I keep? (https://www.scoobynet.com/general-technical-10/1029596-which-cat-should-i-keep.html)

ben.harris 14 September 2015 11:16 PM

Which cat should I keep?
 
I've discovered that the exhaust is blowing on my car, around the turbo. Having looked into what's involved to replace the uppipe and downpipe gasket, it's got me thinking that maybe I should take the opportunity to replace the downpipe with a decat version while I'm at it, as everyone seems to say that this is one of the best performance improvements for reducing turbo spool.

Currently, I'm just running the downpipe cat and have a silenced (non-cat) center section as I didn't want the motorway 'drone' associated with a straight through pipe. However, I do still have my original center cat pipe stored in the garage. As I can't be bothered with messing around come MOT time refitting cats, I definitely want to keep one of them. So basically I'm asking which one is best to have fitted?

If I fit a decat downpipe but refit my middle cat, would I be better off than I am at the moment with a downpipe cat, but no middle cat?

Tidgy 14 September 2015 11:43 PM

Cobra full decat ;)

Track friendly so not silly loud and not droney on the motorway. Still has a nice bark when you give it large though

ditchmyster 15 September 2015 08:06 AM

It's the up-pipe cat that will improve spool.

I'd go Prodrive sports cat down pipe if you can find one.

ben.harris 15 September 2015 08:37 AM


Originally Posted by ditchmyster (Post 11737230)
It's the up-pipe cat that will improve spool.

I'd go Prodrive sports cat down pipe if you can find one.

Mine's a classic, so don't think I've got an up pipe cat. I've been looking at sports cat down pipes, but most seem to be 3" and I'd need a 2.5" one to match the rest of the system. The only suitable one's I've been able to find have been really expensive!

ben.harris 15 September 2015 08:39 AM


Originally Posted by Tidgy (Post 11737183)
Cobra full decat ;)

Track friendly so not silly loud and not droney on the motorway. Still has a nice bark when you give it large though

That would cause me issue at MOT time though. Mine's a daily driver, and I don't want to have to be lying under the car every January (MOT renewal) swapping exhaust parts. :cry:

I'm looking for an MOT/emissions test friendly solution.

ben.harris 16 September 2015 08:13 PM

High Flow Sports Cats
 
OK, so taking this on to my next question - high flow (sports) cats. If I'm going buy a new cat, and just have one, would it better to have it positioned in the downpipe or the middle pipe? Or will it make no difference at all?

Looking at what's available within my budget, it looks like I've got the following options:

Option 1:
3" to 2.5" Bellmouth decat downpipe.
2.5" centre section with 200 cell cat clamped/welded on.

Option 2:
3" Bellmouth high flow cat downpipe (200 cell)
3" to 2.5" decat centre section.

Option 3:
3" Bellmouth decat downpipe.
3" to 2.5" centre section with 200 cell cat clamped/welded on.

I already have a 2.5" Mongoose (I think) back-box, which I plan to hang onto.

Any advice? Would either of these setups perform significantly better that the others or are they all much of a muchness?

TECHNOPUG 23 September 2015 11:58 AM

What is your budget? The Afterburner Sports CAT is 2.5" bore, so you wouldn't need to replace your centre section.

ben.harris 23 September 2015 03:55 PM


Originally Posted by TECHNOPUG (Post 11740553)
What is your budget? The Afterburner Sports CAT is 2.5" bore, so you wouldn't need to replace your centre section.

I did consider that one - it was the only downpipe with a sports cat I've been able to find that ends in 2.5". However, I've just bought a 2nd hand decat downpipe that reduces from 3" to 2.5" where it joins the centre section from someone locally and am planning to refit my OEM centre pipe with cat for the moment. At some point in the future I plan to get a 2.5" decat centre and I'll get a 200 cell sports cat welded into it.

My (possibly incorrect!) thinking behind this is that by moving the cat away from the turbo, although the restriction of the cat will still be there, there will be a much larger volume for the exhaust gasses to fill up before hitting that restriction.

I'm on holiday at the moment, enjoying a tropical thunderstorm in the Florida Keys as I write this and haven't fitted the downpipe yet, so if I'm making a big mistake with my plans and I'd be better off with something like the Afterburner sports cat, it's not too late to change my mind!


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