i want to pose a question. Beyond normal porting techniques (not to be confused with simply going and making things bigger), why would you try to really crazily increase the exhaust flow on a lower flowing head?
What happens on a typical street type exhaust system is the upper lift flow gets short circuited to the max flow capability of the exhaust system itself. So, the 180 cfm exhaust port (flowed naked or with unrealistically short stub) will only be capable of moving about 135 cfm on a 1 5/8 header to a 2 1/2 system.
A crazy flowing port, in a situation like this will drive the seat timing need downward, while still needing the good valve activity on the mid and upper lifts. This means the exh lobe need becomes incredibly steep, impractically steep.
For example, the low lift exh/int ratio may be 90%, but mid lift exh/int may 65%. If you do put a decreased lobe ramp into this combination, the seat duration has to increase, and it takes away from cylinder pressure. To Recoup, the static compression has to be increased. A Similar effect to putting a larger exhaust on a motor and losing low/mid output.
Running a 180 cfm port on a 1 3/4 header to a 3" system is a whole other situation and can really take advantage of the port AND work properly with the intake and also make lobe needs a whole lot more practical.
The valve event needs of lower flowing inlet paired up,with a very high exh/int ratio drive towards very delayed and shortened timing, something that is not available in any ots cams have ever seen.
The cylinder sees the entire inlet path and exh path capability, not just what gets measured on a flow vench with a naked head.
Just throwing info out for to think about.
With all my thoughts on the valve events, i forgot to add a critical part of exhaust porting. The flow path has to be directed into the header , the flow hitting the header at an angle kills all the port work effort.
Case in point, i have some old crane fireball heads that flow crazily on the exhaust side, But the flow exits the port at a crazy angle. On the last set of 351 heads i did, we got 150 and it directed perfectly out of the face at a nearly perfect angle (90 deg to the exit face (header flange).
In the old days, we ported to the mr gasket dimensions and the roof of the port always angled up. Looked great, flowed great, until we got older and noticed where the flow was really going