I don't have the exact ratio worked out on this one, but make sure you put in mostly orange soda, the whole can of milk and then the rest cool whip up to the limit line in the ice cream maker container.
cover after you've mixed ingredients and use the ice cream maker as the directions say. When the machine stops, let ice cream sit and cool more and solidify a little more until desired consistency. We like ours "frosty" consistency.
For an exact replica of a Wendy's frosty: Use the same ingredients, except instead of using orange soda, use store bought chocolate milk. I add a little more cool whip in this one than I would in the orange one.
You can use whatever flavor soda you want for this recipe.