The point here is that this is a live example of how the ever changing CD of an apparatus (Pipe, Port, Venturi, Orifice) has an effect on flow and or it’s retraction to. In this example the CD changed and for the same flow amount we saw almost .4” change in depression. The whole point is in using the variable object (your port) as the reference you could be forever changing and chasing your tail, but in the event where you are continually comparing the flow against a known standard the fallacy of change (In this case) would shine through. Yes I know that in this example the author of the video used restriction to make his point as the air flow change might not have had the same impact to his customer. The pipe acting as a 2.9” +/- orifice the .4 change in depression is only worth 8 CFM and buy gaining 8 CFM of airflow when putting the filter on most likely does not make the same point as showing the increase in restriction when taking it off. All in the light of selling the product.
I have never said the VD test apparatus could not depict changes in effective restrictions, but I do believe it is a far stretch to compare that to valid CFM numbers.
What concerns me is when testing at a static depression that may be higher or lower than what the engine is seeing at the same valve lift, The flow patterns that develop at that valve lift and that depression around the valve and in the port could be quite different and perhaps misrepresentitive of what the engine will see.
Jason,
This is an issue with test methodology and not bench design, a quality flow bench can provide more data than one knows what to do with. A valid test theory implemented through a grounded methodology and followed up with flow test results, dyno results and winning race vehicles are a core part of a successful R&D program
Rick
