981cc for the 920
We now have 95mm 981cc 8.8:1 piston sets for XV920s. Stock, Yamaha claimed 8.3:1. From shear displacement increase there will be more power across the board -- especially down low. To really benefit, while the engine is out and torn down, it would be an excellent opportunity to add sports cams and springs, a free-flowing exhaust, and maybe some carbs. These will fit all 920s: Virago, Midnight, and Chain-drive. Note that you can't simply run thousand cylinders -- the sleeves have a larger OD; they won't fit the 920 cases without some machine work; either to enlarge the spigot hole in the cases, or to turn down the thousand's sleeves a mm or two to fit the 920 cases. Back when I first got my Euro (chain-drive) I ran 96mm pistons and rings (with a surfaced head) for 100k miles until the front head gasket blew, then another 125k miles before the rings started blowing-by enough to make me pull the top-end again. [BTW -- the same rear gasket has been on the engine for 370k miles so far; same pins and clips, and rubber gaskets too] The 95mm "kit" is actually just some cleaned up XV1000 Virago pistons with a set of new after-market rings. They shall be bored into a pair of 920 cylinders, which have been blasted and freshly painted. The greater swept volume into the 920 combustion chamber yields approximately an eight point eight compression ratio. I just blasted the barrels and shot them black. If that does not suit you, the paint will strip or blast off, but keep in mind these are thirty years old; I'd suggest just leaving them.
You will feel a difference. Just leaving everything else as it is will yield gains across the board.
A re-cap: these cylinders have been bored and are sporting a nice 45 degree cross-hatch. I spent some time polishing the gasket surfaces with a buffing wheel -- you can hardly tell. The pins are a slip fit in the pistons, the dowel holes have been dressed to allow easy assembly. Everything has been doused in a light machine oil to preclude corrosion and then wrapped in plastic. I recommend a thorough scrubbing with dish detergent and water just before assembly. Slip it together dry except for a dab of assembly lube on the piston skirts and pins. The dry rings will quickly mate with the cylinder walls and all will be lubricated within a minute of start up.