The intake tract works as an entire system to deliver air to the cylinder. Y'see the interesting thing about intakes, is that no matter what you do, you can never ever get more than 14.7 psi of pressure differential across the entire intake. The carb is designed for a certain flow rate based on that pressure drop. If you streamline the intake tract, it has the effect of increasing that flowrate and therefore require a carb capable of more flow. If your engine is ported with 4 petal reeds, it is flowing way more than the stock crappy 2 petal that the 15 bing is meant for. At that point, you have enough flow that you will keep a steady diff. p across that bigger carb. The flow will be directly related to your horsepower. If you can rev a polini to 16 grand with a huge 4 petal reed, and make 12 or 14 horsepower out of it, you better account for that on the chart.
I dont care how skinny you are, you cant go 60 plus miles per hour on anything with less than 7 or 8 horsepower. You guys that are pushing 65 on your metrakits and polini's have to be making more than 8 horse. My calculations, and testing, have shown 60 mph on a scale model pinto requres 8.6 horsepower to overcome estimated losses.