Hi Vincent,
I can't say for a Sprint, but we fitted a Sue Miller stainless system from the 'Y' section back, keeping the original mild steel headers, to my friends series 3 & the sound is good, perhaps not exactly as an original mild steel system would be, but very close. A nice throaty bark, but not overly noisy, quite tolerable over a long journey without the need for ear plugs. And it looks correct with a " teeny pipe exiting the silencer"
. My own series 4 has an original Lotus mild steel twin pipe rear box with mild steel headers but stainless centre section & sounds lovely from a few feet away, but is really beginning to get on my nerves on anything more than a quick blast down the road, it's way too noisy & spoils the enjoyment of the car. It's something that has got to be changed, so I too would welcome any recommendations for a nice sounding but quieter 'off the shelf' rear box suitable for a series 4/sprint, but had planned to buy from Sue unless anyone knows of a better option. My +2 has a stainless box & pipe of unknown origin, again with the mild steel headers, & sounds just right, again, not too noisy, & with a nice bark, but I fitted a Christopher Neil stainless system to my first +2 & it was horrible ! It sounded really weedy & completely strangled the engine. I guess it was over baffled, & in the end I cut the box off & fitted a Peco box which restored the performance & sounded just like the Lotus original.
Regards, Tim