Ok here is an odd question. I am considering doing a twin turbo set-up. Now here's my question. The exhaust ports are square and the center two ports essentially have a retangular exhaust port. Now I was thinking on making a simple straightforward log type manifold. And I was thinking the easiest way to do it. Since the ports are already square coming out of the head and since this will be a simple log tupe manifold. Could I use square box tubing for the primary tubes at the very least for the center retangular port?

 

You will get stagnation of flow in the corners, so I would not recommend it.

 

Actually the primary tubes will be straight. Like this. Think these only backwards. Instead of back and down forward and up sligthtly. Also after posting I also thought it souldn't be a problem as the intakes use square runners.

 

Intakes use square runners as a compromise between optimum flow and manufacturing cost. Note that tunnel ram intakes, tuned port intakes, and engine designed in the last 20 years use round intake runners.

 

To add to my previous post, the whole point of your exhaust manifolds is to feed as much exhaust energy as possible to the turbos. Anything that disrupts the flow and/or cools the gasses will reduce the energy in the flow and reduce the boost and thus HP from the turbos. Will square tubes work? Sure, but you'll be giving up some HP.