It depends on the wall thickness of the Zard pipes, but yes, it should be close for the peak power rpm I am targeting.
The big deal (in comparing the two) is not the diameter, but the length
and shape of primaries and collectors. The merge collector with diverging cone, and AR tubes in the flanges will alter things quite a bit as well.
I think the Zard and Arrow designs are close, but not quite there. They are forced to make some compromizes due to the production pricing limitations.
I have seen a well designed header gain 3% power and widen the torque band by simply adding a well designed merge collector. But they are expensive (and time consuming) to produce, and can add 50-100% to the price of a header.
The reason I am going with 0.035 inch (0.889mm) wall thickness is to reduce weight and increase interior area. In a 1.5 inch OD, going from 0.065 inch to 0.035 inch wall thickness reduces weight nearly 54% ( 0.065 inch Ti is only about 42% lighter than SS), and interior area increases 8.82%.
The AR cone in the flange will add low end torque and throttle response.
When all of this is added to heads that have increased compression and have a bit of port clean up, power throughout the engine's rev range should increase. With custom cams, even more is possible. But the header design will still work very well with a TOTALLY stock engine.
I am interested in making peak power at a maximum or 9500 rpm, so that the overall nature of the engine and bike does not change. Shifting the powerband anymore than this is not preferable to me. I learned this the hard way with some of the intake work I have done. I can make more peak power, but I lose some of the low end and midrange torque, and the bike's nature is changed.
I do not want to make this bike into a Daytona or Hypersports type bike.
Merge collector (high velocity/low drag):
notice angle of merge and taper of area.
Diverging collector cone(increased expansion/suction):
notice 2 inch stabilization area before 14 degree expansion cone.