angus67, I remember reading about one of the twin engine Bonneville record cars that they were trying to do some ungodly speed in. They ran it all day and couldn't get that last little bit of performance. When they finally got the record run the driver said that the tachs were perfectly synced all the way through. So I guess that's the real trick of it.
My question is what's the advantage of a dual engine bike over an 1100cc bike (or higher)? I get the advantage of more cylinders, but they've been making 4 cylinder liter+ bikes since the 70s, why two XS motors over that?