Checking out the factory exhaust layout. The '3rd Catalyser' placed in the exhaust bay next to the large muffler. You can see the 76mm diameter electronic valve and the small diameter bypass pipe both feeding into the muffler. The downpipes (Y-pipe) are the same as the later 400 series design - too big - with a crushed collector to achieve clearance at the gearbox. The final 76mm diameter bend has a 3-bolt flange to fit to the catalyser.
First basic mod is usually a de-cat pipe in place of that '3rd Cat'. On the Evoras (ones that had the 3rd Cat fitted!) that did make a difference to the decibel count. On the Emira install - maybe not so much. When the exhaust valve is 'open' on the Exige/Evoras the exhaust is a straight-pipe (with some sound moderation) to the tailpipes. On the Emira when the exhaust valve is 'open' it's not a straight-pipe to the tailpipes. With a restrictive/baffled muffler, fitting a de-cat pipe is not going to change the exhaust note by a dramatic amount - unfortunately.
I have the laser-cut 3-bolt flanges now, so I will be starting the R&D programme soon. Dyno first to give me a base to work from. Several different layouts planned from LOUD to trackday 'quiet'. I've looked at the early offerings from a.n.others and let's just say anyone using a bore bigger than 76mm for their de-cat pipe (just because the hole in the 3-bolt flange says so) is ignorant about the 2GR engine or is being misled by their exhaust pipe supplier.