Smokey
-good refresher for me too!
For our purposes- the focus on the bend in the bowl area- I think this is the pertinent part:
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We want to run water pressure through the port and valve and exit into the combustion chamber to see what happens at 0.050 to 0.600 of valve lift. Most water pressure is 30 to 60 PSI, so we need to have a pressure regulator and cut it back to 'bout 5 PSI so we can vary velocity to look for changes. Water will do exactly what air does. You are gonna notice the water comes around the valve from the bottom of intake port where guide ends, to some distance after the valve head in combustion chamber. The shorter the cone the better the flow; the higher the pressure, the more defined the cone is. A perfect 360-degree even cone is affected by shrouding. Anything closer than a 1/2 inch to the edge of the valve slows flow down. And it's possible in heavy shrouding to only flow about 300 degrees around the valve and the other 60 degrees just bubbles, rolls, and twists. You'll also notice, that not a drop of water hits the lower inner area around the valve stem, or for that matter, over a 1/4 inch (at worst) inward of the valve, and you'll notice on the bottom side of the valve combustion-chamber side that it isn't touched by water either.
So you see, swirl in the port and whatever has been done to the valve or valve exit in the combustion chamber is overridden by the huge pressure drop at the valve seat caused by the tremendous increase in velocity. Remember, before that valve cracks open, the air column's velocity was at zero and pressure was at the maximum. That tremendous flow acceleration, accompanied by the sudden steep pressure drop, overrules all other physics. As the valve opens farther, velocity starts to drop and pressure starts to rise, but the kinetic energy induced by the start of the event remains in total control.
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I have his book and it has an even better description of of these phenomena, along with illustrations.
And there is this:
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What's the best port angle? Shallow as you can get-the top of the port up against the valve spring seat. Take any port shape, straighten it out all that you can, and for every degree you straighten it out, with no other changes and for every degree you straighten it out, the more you flow. That's great for airflow, but the compression target has to be addressed.
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I don't have access to my book right now and I've forgotten what he says specifically about guide bosses.