Question for head porters

[War Horse]

Just wondering , when checking for flow on a port, do you install the valves and check the flow by incrementally opening the valve until maximum lift is achieved (from highest vacuum) to the closing point (lowest vacuum). Or does it get tested only by flowing a wide open port (minus valves) at a constant vacuum. Sorry for my ignorance, I have never used a flow bench, and realise that there are other factors involved.

[mayor]

I'm not a head porter, but I think standard practice is to test flow at various valve lift.  Here's a paper on head flow that you may find interesting: HD TC Heads: Flow Bench Study

[War Horse]

Thanks Mayor, interesting , I will have to read this again as I don't understand some of the numbers on the vacuum side of the graphs. I do know that testing was done at 28inhg, but the percentages are inconsistent , in my mind anyway. I just need to know what I'm looking at. Like I said, sorry for my ignorance.