(I THINK) Only if the lower duration cam can't evacuate the cylinder of spent gases. An efficient exhaust port vs a less efficient exhaust port, the less efficient port could use more duration.

 

Right! Especially with the LS rectangular port head, where the exhaust port is much smaller in proportion to the intake, compared to the cathedral heads.

 

Or could it be that the longer exhaust duration contributes to more scavenging of the intake into the cylinder thus allowing more efficient cylinder filling at higher rpms making more power, and that the exhaust port isnt inefficient per say but more efficient at lower rpms and because we cant add more valves so we make them hang open longer, consequently hurting idle quality and vacuum. Just rambling.

 

It's not that extremely different really. Cathedrals have around a 76 percent exh to intake flow rate vs 70 percent on the squares. They both suffer the same thing, one just a hair more.... suffrage.

 

After reading the super chevy article JoeNova posted I don't think I would want square ports in a situation where I was going to have to make a choice.

They made within a couple of horse power of the square ports same cam and using FAST 102 intakes, but the cathedrals should be a bit more fun of a driver head.