Exh manifolds in an Early A...

Treblig said

You will be going from 1 5/8" to 2.5, the resistance to flow is proportional to one over the radius squared, so if the radius (or diameter) is cut in half, the velocity of the fluid will decrease by a factor of 2^2 or a factor of 4. So in a pipe 1/2 as large, 2.5" down to 1.25", flow will decrease 4 times. This is true for fluids in a pipe I'm not sure about air flow but I do know it decreases dramatically.

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Just to stir the pot, velocity, flow past a point and "volume" are all different parts of the same thing. I'm only thinking out loud, not a flow export but it "seems" that, yes, the velocity would decrease, and the flow past a point would decrease due to the enlarged cross section. A river passing a million gallons of water over a rapids, still passes a million gallons of water at a wider point, it is just spread out. The total volume of water is the same. No?

So yes, I agree the flow rate at a wider cross section will be slower but the volume of gas should remain the same?