Thanks for that
It seems my car has in the past been retro fitted with a tail-pipe from a smaller engined car, a 2000 or 2300 perhaps, because it looked terribly small to me, and having owned 2600s, 3500SEs, Vanden Plas's (?) and Vitesses before I never remember them being this small....
Maybe it was done at a "Kwik-fit" type establishment some years ago, and this smaller bore tail-box was the only remaining SD1 stock they had left at that time.
I can't measure it because it came off from the back of the rear box and is lost
I may approach a local company who makes up exhaust systems and get them to build me a tail-pipe, perhaps losing the rear box altogether, should give me nicer deeper V8 rumble
Jay