For any given engine, there are 3 ways to improve performance. Make it Bigger - easily done Spin it Faster - if it can't breathe, it won't spin faster Improve Efficiency - porting, cams, carburetion, ignition, friction elimination
Porting is about improving efficiency Let's keep things on a very simple level to start with. A flow bench measures the amount of airflow passing through a port. That's it. It's not mystery. It's not rocket science. It's a measured value. It's meaningful and it's meaningless at the same time. CFM is an indicator of what can be obtained in Horsepower if everything is working properly as a system. But just measuring and knowing CFM capacity is only part of the information you need. 
Velocity is an important part of the picture as well. It's velocity that indicates potentials and problems. It's very important to test velocity with a velocity probe [pitot tube]. You can see the local velocity picture of the port. You discover fast areas and slow areas. The trick comes in balancing everything out to help keep the velocity as equal as possible throughout the port. That prevents air separation and turbulence. Initial Analysis Prior to porting, each cylinder head undergoes a comprehensive analysis to determine the requirements for the intended purpose of the engine. Crucial aspects of the engine's components are entered into a special software application and requirements to meet the design goal are determined. Port lengths, cross sectional areas, valve size, bore, stroke, connecting rod length, camshaft parameters, mean piston speed, intended Peak Horsepower RPM are key data elements that comprise the total engine package. We evaluate all of those in order to establish the proper port dimensions. You don't get off the shelf port work. You get port work designed for your specific engine. Once the design criteria has been established, an initial baseline flow of the cylinder head is performed, documented and charted using FPexcel. This is a software spreadsheet application I wrote and sell to other porting shops. It's being used in the USA, England, Europe & Australia. 
Looking at valve and port coefficients, calculated and measured velocity allows us to establish the potential of a particular cylinder head to produce power. We monitor flow data during the porting process in order to maintain correct velocity profiles and ultimately the proper port sizes in critical areas that will help your engine produce more power. Upon completion, your head is shipped back to the customer with complete flow analysis data. 
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