the flowbench really dictates the minimum flow capacity requirements only. The cam redline pretty much sets the flow need initially. Then it's more of the porter's experience with different r/s ratios and engines (here's where the science ends and the black art begins) which determines how and where they change the shape of the port...the overall port size can also be tested empirically using pressure manometers and pitot tubes which measure flow speed for 1 stream of the many parallel streams or layers in laminar flow. I believe I covered the equation for redline determinants of cfm and vacuum based flow equations over on the "Gotten Head Lately?" article over at Hondavision.com's Tech Review article section and I also state the Bernoulli equation using the measurements off the pressure manometers and pitot tubes placed in a conduit (head port).Jacksont001 on Sep/03/02 said:hmm, Mike I know you have addressed this before. in all your articles. port sizes are designed flow a certain volume at a certain speed. what speed would this be? the reason I ask is so we can develop a primer based on swept volume vs. rate of fill over time(based on piston speed) + total time valves are open (based on cam profile) so they can get an Idea of the flow requirements from start to finish and the size(quantity/quality/velocity) requirements for each step along the way.