moper
Well-Known Member
If you have control over the shape & size of the hole in the flange and we're still talking N/A I'd aim to keep the same size as the port opening on the roof and "outside" of the first bend in the respective primary tube. The "inside" and floor really don't matter much IMO in that scenario. If you're going to turbo(s) the same size and shape would be best case and don't make the header primary tubing any larger between the port and turbo flange.
