The trigger wheel tells the electronics of the bike when to fire a plug. The "trigger wheel" is the same thing as a TPR and is attached to the end of the crank. The trigger wheel was designed to advance the timing 4 or 6 degrees on the 1500 Wings and Valkyrie.
The biggest difference between the 1500 and 1800 is the computerized fuel injection. Timing could be played with on the 1500 because of the lack of the state of the art computerized engine controls. The 1800 has the computer controlling all of the timing stuff. I would be surprised if changing a trigger wheel could do anything for the power. I think the only things that could be done for performance is: Better air flow (both in and out) and some kind of modification to the ecm (computer) for better fuel control.