Orifice in a Tube

[DFab86]

Not to bump an old thread. But is this possible using a single shopvac or even multiple shop vacs? I've seen several designs documented. I was looking to flow test a set of exhaust headers and compare the real world to CFD analysis. I'm curious if I need to spec the orifice differently for a tube design. Also I'm ok with converting to 28" if that's not feasible with this design.