Exhaust header design

[t walgamuth]

I am removing the head on my Formula ford race car and notice that the exhaust header pipes must be at least 1/4" larger diameter than the ports coming out of the head. I tried to read a bit about it and it seems that bigger tubes will raise the rpm level at which torque peaks and longer pipes do the same.

I am thinking of making some pipes which are smaller diameter and lots shorter, like the 37 Auto union racers with the shorty pipes exiting straight out and no collection at all. Lower torque delivery and lighter weight.

Anybody with expertise on these here?