HarleyTechTalk

did you ever think a standard Twin-Cam ports are around 2inchs in length. not much to work with. so lets discuss what we can do in those 2 inches of port length
VALVES: we can change the valve diameter for sure. on 2in valves beware of TDC lift. Valves also come in many different shapes than help or hurt air flow.Port design and valve seat profiles come into play. also a larger valve the throat ratio has to be adjusted. the normal throat ratio are from 89%-to 92%..
VALVE SEAT Profiles: remember all air that flow through a head needs to flow through here.
Contact seat angle: the standard is 45 degrees, this can be altered.the contact width is normally around 1mm-1,5 this canoe altered.
INTAKE SEAT angles or radius: it seams intake seat like angles or break in the profile , remember to design to get proper throat ratio. beside contact angle the angle above this angle is know as the critical angle and directs air into combustion chamber
In  head porting the inch above the contact angle and the niche below the contact angle is where the magic of enhancing air flow an port velocity. The cross sectional area of a port comes into play in this area below the seat and how the short side radius is designed
Exhaust Port: I see the standard now is a radius type seat.Seeing a lot of reverse radius exhaust seats
Valve Guides; the standard seems to be a nickel bronze type
Combustion Chamber is very critical in design to unshourd the valve as it opens. the radius of chamber comes into play
Advanced head designs we are  seeing the valves seats pockets bores being off-set these designed heads flow lots of air and amazing port velocity. this design can be implement in the stock Harley heads
Isotropic cylinder head components are becoming the standard in performance cylinder heads
Valve spring design for you cam lift is a must
Textured intake ports and combustion chamber are becoming the norm with a sanding rolled exhaust port.