1bolt,
Thank you for the reply.
I have been doing my research and I came to the same conclusion as your advice. Actually I had thought that the orifice plate setup was simply "the next level" if you will since you can calculate actual CFM from it as per this post
DIY Super Accurate Flowbench
I didn't know it was an absolute must (though it seemed that way since my setup basically sucked)
Along the way I found some interesting information about orifice plate flow meters. I also found this great calculator to determine flow through an orifice plate of a given size amongst other parameters... you might find this interesting:
Flowrate Calculation for an Orifice Flowmeter there are several generic tables for air density vs temperature. At 25 c (around room temperature) its 1.18... the default value in that calculator is 0 c
Anyway, do you suppose a single 6.5 hp vac will be enough to flow a head that will be under 220 cfm? The stock buick V6 head is pretty horrendous, I believe at 28" it only flows 150 -160 cfm and max ported heads only get somewhat near 220.
According to the calculations I made using the link above, I came up with a 1.25" orifice plate. What size orifice plate do you use or recommend?
I did figure out my manometer fluctuations. I put a restrictor in the manometer line.. All I did was get a needle valve with 1/8 npt threads where I installed 1/8 npt to 3/8" barbs. The needle valve allows me to precisely adjust the dampening. Of course this has no effect on the consistency.
One last question for you, what is the calculation to figure out cfm of the item you are flow benching? I see how the calculator I posted above arrives at the cfm value of the orifice.. but then how do you go from there?
I'd like to make a similar spreadsheet (or if you'd like to share yours, I'd appreciate being able to check it out)
Thanks again