Rounded 45 radius using a Quikrete tube.

[Knocker]

Had to do a 45 Bend in my port but wasn't too keen on using a 45 flat piece of wood since I thought that might disrupt airflow. So since my port was exactly 5 in in diameter I found an exact 10 inch diameter Quikrete tube at Home Depot. Then I did this...

[Knocker]

I measured 18.75 in which was the exact height of the port then used a zip tie as a guide and cut it with an oscillating multi tool. Came out perfect

[Knocker]

 

Then I cut exactly one quarter of it (45°).

[Knocker]

Then I test fitted it into the port bend and sanded down the edges (yes that's a spider).

[Knocker]

Then I glued, caulked, and taped it. It turned out to be rigid enough to where I didn't have to fill the space behind it with foam or whatever. Now my port is exactly 5 in in diameter even throughout the 45 degree turn radius and I'm sure there are less little vortices coming off of the curve as opposed to using a solid flat 45 degree transition.. I don't know if it made any significant difference but I can't see how it didn't help, especially at high port velocity near tuning. I'm curious if anybody else here has done the same thing. It was easy and fun to do. Hope this helps anyone who decides to try it.