Originally posted by mtber
From Tials site:
Flow capacity. Contrary to popular belief, larger higher HP applications do not necessarily require the largest wastegate available. The lower the boost pressure you are gunning for the larger your wastegate needs to be. An engine/turbo combination that is set to 25+psi has a smaller wastegate flow requirement than the same application set to 7 psi. This is because the wastegate is used to lower the boost not raise it, the lower the boost pressure is set the more flow the wastegate must allow.
Exactly, except for the fact that you have to add engine displacement and compression into the equation. The more exhaust gas energy you produce the larger the wastegate may need to be.