Port Limitations

The limiting factor for real horsepower "overload" for XV/Viragos lies in their ports. There is too little material around them for enlargement, and they bend severely, choking off airflow.

On Gen I's, the frame -- and to a lesser degree -- the fuel tank limits where the port can end, the manifolds/flanges that can be used, and the size and configuration of carburetor(s). I see 920R/TR1 enthusiasts cobbling up adapters for FCR's -- but they leave the basic ports intact.

My assessment? For a little more flow, enlarge them slightly to match carb flanges and pipes; for a lot more flow: straighten and move them, maybe enlarge them. The valves are pretty big, and the ports are plenty sizable, just crooked as a cork-screw.