ben.harris

iTrader: (2)

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

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

iTrader: (7)

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

iTrader: (2)

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

iTrader: (2)

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.

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

ben.harris

iTrader: (2)

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

iTrader: (1)

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

ben.harris

iTrader: (2)

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!