Does that mean cat is further down the exhaust or am I miss under standing , I know with a turbo you need back pressure to stop it over spooling but didn't realise you need any back pressure on NA setup, or is that what helps with the sound

For a normally-aspirated 2.0 Coupe, back-pressure is wanted & the optimum pipe diameter after the cat. (which is contained in the exhaust manifold) is 2.25".

Turbocharged & supercharged engines do not require back-pressure, so cat-back diameters of 2.5"/3" work well.

I would recommend Longlife Exhausts to build a quality stainless, mandrel-bent system onto your car `while -you - wait`.......you get a lifetime guarantee & the quality is FAR better than the likes of Powerflow!.

Nick.

And up to 2.5" for a NA V6 Valk? (please say yes) Mines probably getting seasick as I write, hopefully bobbing over from Korea. It will have inserts to reduce the sound level slightly.

Yup!.......a 2.5" dia. catback system will be fine for the 2.7 V6 Delta engine.
http://www.longlife.co.uk/

Nick.