The Zen casting will not allow the porting that this other guy designed, so no, your right, we won't see that kind of power in a Zen piston port (naturally aspriated).

Hey Dave man. If ya make more, I do have and sell a great manifold for it. It might save you some time, and it matches the port very well. It rids the manifold/pipe joint of any weld beads or steps that almost all other manifolds have. Unually, the engine will run smoother, and get more top RPM, but some pipes actually showed a good increase in hp. It has been distrubeted by TGN for about 3 years now. It is 3D machined on the inside from both sides with a CNC mill to give a smooth transition from the rectangal port, to the round pipe. Most Ped racers use them today because all stock manifolds are more restrictive and need to be matched.

http://www.teamgonads.com/Merchant2/...egory_Code=PFM

It fits a header pipe outside diameter of .875" +/- .015" (It's machined to a .890" diameter)