I understand what your saying but heres the numbers that lead me to my decision. I have dash 16 coming in to the block. That's 0.880" ID. Right out of my sea pump theres a dash 16 T that has a reducer on the T down to dash 10 that runs off to my intercooler. So, we have 0.880" ID hose going in and dual dash 10s going out to the exhaust. Dash 10 is 0.563" ID so my theory is that since the volume of the dash 10 hose X2 is 1.126" and ive only got 0.880 coming in, There wont be any restriction. In fact, the water should flow easier through the 2 dash 10 lines then it will the single 16 coming in. Going to a larger hose will only slow the water down as it will have less velocity, which shouldn't matter anyways. Now if im wrong, please let me know. These are just my thoughts.
You are way wrong with your figuring... Its radius squared times pie... you can also figure hose resistance in there too if you want. but a number 16 AN is .608 sa and two number 10's equates to .4978sa,,, So you are creating back pressure with that setup.
