Thanks to everyone so far, it's been really helpful and food for thought.
My current usage varies between predominantly long distance for holidays/touring and stuff and a bit of 'round town blatting'. So I'm erring towards a rear exit at the moment.
Currently, she's on a rear exit, with the rear silencer removed so I get a good sound out of her, but as others have mentioned, she does get a bit 'boomy' with the hood up.
My Dad used to have swappable tail pipes on his Plus 4 - he called them his summer and winter pipes - summer was a side exit, winter was quite a long rear exit. I could always go for that option and have the best of both worlds....
Does anyone want to buy a kidney so I can get the manifold?
