I use 30w non detergent in my V1. 20w is hard to find, but 30 you can usually find at Ace hardware. It's used in air compressors so it's easier to find it at a hardware store than at an auto parts store.
The V1 uses one pint. The oil check screw on the case is about 1.25 pints before it leaks out.
On mine if I fill it up till it drips out of the check screw, it'll leak out of the breather while riding.
So what I'm saying is, use one pint.
Detergent oils foam up, too. Which can destroy your seals, deteriorate your clutch pads, and blow out of your breather cap.