I'll try to keep this as politically correct as I can. Any carb is a restriction on the induction at WOT. the smaller the carb, the higher there restriction, bigger less. With higher restriction the engine has to use more power to pump the air in. So the first part of the equation is making the carb as large as the engine will tolerate.
For the second part, why not just put a huge single or pair on it? It's because of two reasons, signal to pull fuel in and how well the fuel is atomized, vaporized, and equally distributed to each cylinder. In this case the smaller carb provides a higher vacuum or pressure difference. This pressure difference is like how an air conditioner works, the change in pressure will make the fuel vaporize at a lower temp and that aids in induction cooling, homogenization, and distribution.
So now that you see both parts every engine will have a balance of how big the carb can be. Now you can skew those numbers a little, by making the carb do a better job of atomizing the fuel, and tuning to provide equal distribution. Using a single four barrel will almost always make less than two, even if you could equal the single carb to flow the same as two. The reason is distribution.
So now we have the big single hole carb. How do we effectively manage distribution? Sure you have jets on each corner, but the discharge area is small compared to the hole area, leaving a lot of dry flow. Now if you put one on any particular engine and distribution happens to fall in line and the tuneup is real close, then it will run reasonably well. If distribution is not so good, then you might chase your tail trying to make it work. I had a local guy run one, for him it ran well. As soon as he made some engine upgrades it wouldn't work, kept burning pistons.
Look at this video, and pay attention to where the fuel is mostly distributed. Can you see what cylinders might end up lean?
