HunterB

Forgive my ignorance, but can anyone tell me what a cat back box is/does in the exhaust? It's been suggested I get a bigger one!

Thanks,
Brian

alistair

It's a back box with a large pipe. The standard UK car comes with a twin mouse backbox, the scoobysport is more rat sized, but you have to go for one of the aftermarket items to get a full cat into it

harryh

So, in other words does it replace the existing pipe from the "cat back"wards? Also would it do the engine any harm to fit a Magnex 6"x4" backbox before the car has been run-in?

alistair

Your exhaust comprises 3 sections, a downpipe which connects to the back of the turbo and contains the first cat. A mid-section which also contains a cat and a back box which is a silencer. Fitting a Magnex back box will not harm the car, however, it may invalidate your warranty.

HunterB

Thanks for the replies. My car is a '96 Legacy RS. It already has a fairly large rear silencer with the exhaust entering the silencer in two pipes and exiting through a single four-inch diameter tailpipe. There's an inherent slight problem with the twin-turbo setup - a lull in the boost at around 4,000 rpm as the smaller turbo runs out of steam and the larger turbo kicks in. I've been told that a larger "cat back box" cures the problem, but I really don't want to have a tailpipe that looks like the end of the Channel Tunnel

Any further advice would be gratefully received.

Thanks,
Brian

Sith

Hi,

It sounds as though they mean you need a larger diameter tubing through the system rather than a tail pipe that an elephant could hide up (HKS Super Drager et al.)
A larger pipe bore will allow more gases flowed through the system. This allows for better performance. But if you go too big it upsets the back pressure and ruins performance.
You could also find that there is normally a gap between small and large turbo. Not having driven this setup before I can't be 100%
This is as far as my exhaust knowledge goes. No doubt if I spouted any rubbish I will be told