If all the stuff before combustion had to go infront of the cylinders, then the engine would be under the seat, and the C of G would be no-where near 50:50, as you plus engine = most of the bikes weight, all sat on the back wheel!
Carbs need still air to work properly, and although injection is much better at dealing with forced air it's still easier to work with still air (even if it's pressurised by forced air or turbo's) hence the continuing need for large airboxes.
Why a V twin then? Because it has better primary balance than a parallel twin (I think) so it lasts longer and saps less power.
Manufacturing expansion chambers to fit between the frame rails would be another pain, and the heat transfer to personal body parts is quite uncomfortable I am led to believe! Not to mention frying electrics...
Perhaps a leteral V twin (like a Guzzi) would be best, with a central airbox and rear facing exhausts. But then again, exhaust length is an issue, so the pipe might end up on a trailer to get the proper length!
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
