Originally Posted by 1Gary
Now porting.RHS during a R & D research found after all the yrs of porting they have done professionally,and their best guys,couldn't port match any better than 25% and that it was very labor intensive.Now these guys I know and they have the best of the best flow benches anyone could have. BTW-you got a flow bench at all??. You need that. They constructed the CNC programs for 5 axis porting.It produced port matches that are within 5% and cut down the labor time to 8 hrs. The shape is as important as the sizing.You really need a good understanding of air flow dynamics. But one of the things RHS said was more important than the size of the ports is the cross section of the port.They added in there are many "rated" ports out there that plainly just don't flow as advertized.I know for a fact the production Vortecs stock are about 165cc intake runners and your damm lucky if you can get them to open up to 170cc's before running into water and what's more the rough intake runners is what makes Vortec's suspend the air/fuel mixture.Smooth port them and you destroy the Vortec effect.What you can do to the production Vortecs is to clean up the exhaust port to help them out.You see there is a reason behind the 180cc and 200cc Vortecs.Here again I am very sure about this.
You are correct. "Port profile" is very important, which is why aftermarket race heads have very different castings over stock heads. "Port location" and "profile" along with larger valves are why aftermarket race heads make more power. Also the valve pocket areas play a role.
In every serious race head you will ever see, the port locations are raised.
Some of them are radically relocated.
You will never achieve this with stock heads.
Intake runners should always be rough. Minimizes seperation.
Chamber and exhaust side can be polished smooth if desired. Usually doesn't result in any power gains, but can help minimize carbon deposits.