Downpipe and Cat

**mitch_gti** · 28-11-2007, 01:09 PM

Going to visit one of newcastles best exhaust shops on monday about downpipe/cat changes.

The guy said $495 will get me a 200 cell cat which complies and actually exceeds euro4 emmision regulation (he mentioned it meets California emmision regulations).

He said he will obviously have to fit the bungs for sensors. Can anyone see any problem with this? i dont want to have to have the car retuned or any warning lights.

Going to get him to do the downpipe section too. Free up some ponies.

**Timbo** · 28-11-2007, 01:20 PM

You don't have to get a new cat unless you want to return the car to stock at a later date -- saves some money and the stock cat isn't all that restrictive. If that's your plan, makes sure returning it to stock is an easy job.

No problem with the sensors, as long as the installer is careful about placement. The stock plugs really should have the ability to rotate, so the wires don't get too twisted. Just mention that to him.

Finally, ensure he gives a reasonable length of flex joint in the down pipe, as the Pog engine moves a great deal (see my thread on loose turbo bolts) and can cause problems.

What size down pipe are you going for?

**mitch_gti** · 28-11-2007, 02:04 PM

Hmmm... i would have thought the standard cat would be quite restricted.

I would have thought 2.5inch mandrel bent stainless downpipe and 2.5 inch cat would be enough.

Or am i off the tracks

**SoVeReIgN** · 28-11-2007, 02:24 PM

The standard cat IS very restrictive.

**Timbo** · 28-11-2007, 02:37 PM

I've not seen any evidence supporting that claim. Happy to change my mind if something is produced.

2.5" should be fine, but you can go to 3" on the downpipe if you want to. My exhaust guy gave me a lengthy explanation about pipe volume restrictions arising from bends which convinced me to go 3".

**mitch_gti** · 28-11-2007, 02:44 PM

ill have a good chat to him when i visit the exhaust shop.

I would have thought that 2.5inch cat and 2.5inch dump would have been better because wouldnt it be smoother flow if its all the same diameter?

If 3inch dump and 2.5 inch cat is best thats what ill do.

**GT3** · 28-11-2007, 02:56 PM

Originally Posted by Timbo

Happy to change my mind if something is produced.

lol ..no you won't

this issue has been hammered... it all comes down to $$$ and what you're after. the std cat is restricted compared to a high flow, sure. many exhaust specialists will tell you that's there's little point increasing flow through the cat if the rest of the system is still restricted - defeats the purpose. in that respect, I agree with Tim, ie dump pipe is a cost effective upgrade to stock system on its own - if you're doing the cat then its logical to do the rest of the system too.

**mitch_gti** · 28-11-2007, 03:06 PM

Is a 200 cell cat considered high flowing?

**Timbo** · 28-11-2007, 03:51 PM

At 2.5", it should be fine. The main thing with cats is to ensure they are "reputable" in that they are actually stamped with the claimed environment approvals. There's a lot of cheap stuff out there. Also, you should ask if the cat has any resonance as this can lead to the dreaded droning exhaust. A good shop should know all this.