I have a 1999 K1200 LT I was wondering if anybody has ever changed the airfilter airbox to one off a 2003 K1200 RS they look like they have larger air velocity stacks going from the box to the throttle bodies, I know it would probably move the HP and torque numbers up the RPM range would the computer be able to handle it anyone know and what difference in gas mileage and power?
Of course the air-box is different on K1200RS, however this only a small part of the equation:
1) K1200RS have higher compression pistons
2) K1200RS have different camshafts (intake and exhaust)
3) K1200RS have larger throttle-bodies (34mm for early K1200LT, 36 for K1200LT 2004-2009 , 38mm for K1200RS)
4) And OF COURSE the Motronic-EFI sysetn is tuned differently according to effects of all above items.
In my opinion, you will achieve noting (or very little) by changing only a single small part of this whole system. Unless you modify all the above items, or install a K1200RS engine (with its matching ECU) you are on wrong track ;-)
The 2005-2009 K1200LT horsepower is somewhere in between the early K1200LT and a K1200RS, because they have increased compression , changed Camshafts profile, and increase the throttle-bodies by 2mm. Not enough to acheive the full 130HP of the K1200RS, but better tuned for low end torque - something a 900 lbs beast needs...
P.S.: Did all this typing for nothing.... as I saved my message I just saw Jzeiler has given you roughly the same answer ;-)