I think any reasonably made x-pipe will be better than factory H-pipe overall but H-pipe might deliver a bit more torque at low rpm at certain scenarios. There is no such thing as best x-pipe for all conditions, it's a compromise. Pipe size, location, entry and exit angles as well connecting cross-section will determine at which rpm it will increase torque more. If you want to make it simple and generalise then steeper angle and closer to engine will increase high rpm torque and max BHP at cost of low rpm torque. Shallower angles and further from the engine will give more low end torque at cost of max BHP.

and none at at sounds really good but I have no idea what it does to power :D

You could make the new system so that the x section is independently removable, then you can play with different styles and see what it does.

That's the usual wisdom of X-pipe vs H-pipe (that X-pipe surrenders some low end torque).
However the one I have been looking at that was developed for Porsche 928 seems to increase torque across the whole range.
http://www.performance928.com/cgi-bi...ss_parent=1128

But on the other hand will it work well with Audi's 4.2 V8? How different is the 928's V8 from the Audi V8? who knows.

I would think any X-pipe works better before the cats, not sure that the cross-over can pull the gasses from opposite bank as well through the mesh of the cat. I'm not sure if there is enough room in the D2 to put it before the cats.

I'd have to disagree about the sound Mikki, I had a x-pipe on my previous S8 it sounded gorgeous. Also just check out some of them on youtube, they sound very good.

https://www.youtube.com/watch?v=QbaSAxgxtPc

https://www.youtube.com/watch?v=nqrufMqTQpY

I'm not saying an x pipe doesn't sound good, just that no x also sounds good :)

This isn't the vid I wanted, but it'll do.

https://www.youtube.com/watch?v=mANtLFlyYrw

I tried open downpipes with my old V8 too. Thats also interesting :D

Yup that sounds pretty damn good :)
You inspired me to find a no-exhaust video

https://www.youtube.com/watch?v=N26o9C5OBY0

found a better one, wow this is amazing!
https://www.youtube.com/watch?v=KkglRtuqDt8


Just chopping out the rear box sounds amazing too!

https://www.youtube.com/watch?v=SYLUfVVCkb4

Yes it does, I've done that on my D2 and it sounds awesome - deep boomy v8 when driving and like that video you linked to when you floor it! +++

Hi,

On my previous LPG car (V6 Vectra) I removed the CAT as LPG clean enough to not need it.

Sound improved no end...

Robert