Johan K

I guess that an empty cat refers to a cat that has been totally stripped out of its contents, i.e no more honeycomb.

My RS has an empty cat, cup exhaust, K/N filter and a drilled airfilterbox. The noise is absolutely awesome! The empty cat provides a free airflow but I am not sure whether it actually results in more HPs, maybe it just makes things worse? Plus the car does not pass emission tests (I have a honeycomb cat to install for the yearly inspection). It makes a wonderful noise though .

Gavin

The original exhaust tip will make the car slightly quieter, as it does not act quite so much as a trumpet. If you want to do track days, I would suggest that you go the g-pipe route. This will allow you to enjoy sound on the road. When you have a track day booked, simply take off the g-pipe and put the original box and tip back on. It only takes 5/10 minutes to do and you then you know you can get on the track. When I was at the Bedford Autodrome I was running a g-pipe and lerger tailpipe with no cat and and a cup airbox. It failed the sound test, they let me on to see how loud it was, but soon black flagged me. Fortunately I had taken the original back box with me. I was back out on the track within 15 mins and no more trouble.