Many Exige 380/Evora 400 owners are new to Lotus and I'm using this page to give some information on their present exhaust design. The differences between the early and later systems are: Early downpipes - 51mm diameter. Later downpipes - 60mm. Check out that 2-1 merge collector on the Later design - almost a T-junction! Flattened for clearance too - not great.
Early link pipe (between downpipes and silencer) - 63.5mm. Later link pipe - 76mm.
All of these pipe diameter increases are to reduce the exhaust back-pressure. Those UTC's (Ultra Thin Catalysers) in the factory manifolds/headers are under increasing stress with every new model released and the attendant power hike. We're up to the "430" models now! They can't remove those manifolds/headers, (much as they would like to!), so they open up the exhaust further down the line to reduce the stresses. Unfortunately, bigger-bore exhausts are harder to control noise-wise.
Early silencer: check out the comparison images. The valve merge pipe on the early cars appears to be more efficient flow-wise. Both pipes are 63.5mm, although the valve "closed" pipework reduces to 54mm internally.
Later silencer: again, looking at the comparison images. The valve merge pipe has a smaller(!) "closed" pipework - 48mm. With a connection to the larger/LOUDER 76mm merge pipe, they had to keep it smaller/quieter than the earlier design to help pass the EU drive-by noise test.
Some Evora S owners would like to have the exhaust sound of the 400 series and any exhaust fabricator can make that 3" (76mm) system fit to their 2.5" (63.5mm) link pipe BUT if they want the authentic 400 sound they ALSO need to fit the 2 3/8" (60mm) downpipes. Do that and you wouldn't need to modify anything, just a straight swap - and with the bigger-bore pipework you would a LOT of boost and power - so you STILL wouldn't sound like a 400 series motor. ;-)