I bet 2 will be plenty to take 3 cylinders. They ran them back 10 feet to the merge per an old ramchargers conversation. That was a stock cam profile so your mileage may vary.
Nothing naturally aspirated needs back pressure. That's a common misconception. I have planned a very similar exhaust for mine. I plan on 2" primaries going into a Flowmaster wye and then into a single 3" pipe.
Yeah after looking at some picture of the dutra s split looks like a lot of people are running 2.25, I'll probably run 2.25 to flowmaster y that exits to 3 inch then reduce it back to 2.25 I'll keep you guys posted.
