David Vizard wrote:
Rick360 wrote:What variables go into calculating port energy? Velocity I assume ... but is it average port Velocity or at MCSA?? Flowbench velocity or running velocity? and area is probably included ... but again the question of which area ... avg or min? What about engine or cylinder cid or port length? What all is used to determine this Port Energy calculation?
Port energy uses mean area, CFM, resultant velocity and mass of port air. The real comparative deal here, and it is not in this current program but will be, is the 'port energy density per foot length'. With this you can make caparisons across the board including 2 v vs 4 v heads.
If you need to know the mean velocity at any give point down the port you can enter that area instead of the mean area.
The Mach Index uses the mean area and the numbers generated are by my method not Charles Fayette Taylor's. My method returns numbers more akin to high rpm engines not blown 2800 rpm 2800 cube units Taylor experimented with. Beautiful though those big radials are I don't have a Bear Cat, Thunderbolt or a Corsair to put one in.
Seems to be the flaw there is that flow benches use room temperature air heated to a value determined by the vacuum source motors while running engines use significantly hotter exhaust gasses. That undeniably changes the resultant velocity value. This is one reason why flow benches are less than adequate for thorough exhaust port analysis unless corrections are applied to compensate for such differences.
One can use CFM/Sq.In with measured pitot velocity and / or calculated mean velocity to derive data of equal relevance. It's all just numbers and they can be manipulated to show any value that may be helpful to paint a picture.
What precisely is "port energy density per foot length" and why would you measure in feet when no such port length would ever exist?