exhaust pipe diameter for a mildly modified 340

Correct, i've built a few cars and maximum power or racing is not important, but when i step on it
something has to happen.
I actually bought a complete inexpensive used 2" exhaust just to get me driving when i reach that
point with the current project.
So i thought i would see what some of the more knowledgeable guys on the site thought about how
much would be left on the table? Maybe it will be adequate