This might seem like a stupid question but should I port out the TB openings on the plenum, if I'm switching to a larger TB. I mean the flow characteristics can only be as good as the smallest/narrowest part, correct?
If not, can someone please explain to me how simply bolting on a larger TB increase flow?
Thanks in advance.

Yes port the plenum to match the TB, and knock down any obstructions (egr walls).

nick

Before you buy a TB, Do a search for TB and My Name.

And TB and my name.

A 58 really is too big for a stock plenum. You should see what you have to do to make it fit reasonably nicely.