Everyone is different, but there's a point at which more oil is just that - more oil. The liver can only spill out so much bile at once. If you take in too much, you feel awful and queezy for a LONG time. So if you dno't know your limits, start out small and stick with 1/2 to 1 cup of oil at most.
I take 1/2 cup oil to 3/4 cups juice. 30 minutes later, if I'm not burping and queezy, I take another dose. I keep it small because I'm a tiny person. ;)
If you want to maximize your flushes, then be sure to take herbs to cleanse the liver and increase bile production.
Hope that answers your question! :)