How much oil a engine needs is pretty much dependent on the RPM a engine makes. The higher the RPM, the more oil it should have generally. Thats why Zen suggests 25:1 I am sure. I run 28:1 with Maxima Castor 927. I allways liked castor oils, but in the old days they could get pretty gummy (and actually gum a ring in a piston groove). But this oil is a castor/synthetic blend, and runs pretty clean with good jetting and fuel mix. This oil has a high flash point compared to a lot of other oils, and I think it can handle the heat a bit better than most. But that is just my opinion. Oil is a personal preference, and there are a lot of good oils out there. It seems, when you find a oil you like, you tend to stick with it.
Here is a neat little measuring cup that measures any ratio you want for 1, 1.5, 2, and I think 2.5 gallons. Liters may be on there too, I am not sure. I would not mix without it.
http://www.davesmotors.com/cgi-bin/s...9247fa14dd4780