Eddy vs Holley CFM ratings?
So what you are saying is the bigger the carb the more HP it will make?
Not really, the carb rating is arbitrary it's based on at what vacuum level your reading it at.
Think of it more likes headers we know 1 5/8 goes on a mild engine 1 3/4 on a healthy one 1 7/8 on a healthy stroker etc...
All will move the same amount of air but smaller you go the more restrictive they become robbing hp. But as you go bigger there's a point where the gains get smaller and smaller and may rob low end efficiency.
Same with carbs going too small just throws away hp. Like say a 390 4bbl might kill 50 hp over a 750 but a 750 might only lose 1 hp over 1050 on a certain engine.
The main reason you got to match carb with engine and not just go for the biggest is cause of tunablity. On a drag race only car basically you only got to worry about idle and WOT so you get away with a bigger carb. Look at the Holley sniper efi they don't sale a 550/650/750 etc.. (different restrictions) They sale one for 800 hp or less so it's good from a /6 to a bad *** 800 hp 572 inch stroker. The only reason to add restriction on your engine at this point is so all the carb fuel mixture circuits will work and only need just enough to do so or your throwing away hp.
Also look at that formula that tells how many cfm your engine needs that's pretty accurate.
But here is where it gets tricky. That has nothing to really do with what carb you need.
Let's say that formula says you need 550 cfm. Doesn't mean you grab yourself a 550 cfm carb and be done with cause basically any carb you put on that engine technically becomes a 550 cfm carb from a 390 to 1050 will all flow about 550 cfm on that engine cause what will change is the vacuum level (restrictiveness) at WOT. So you want to pick a carb the will give you the right amount of vacuum. A full race car might go under .5" a street/strip might go around 1" and if you don't care about throwing away hp for mild street 1.5" aka a 550 cfm carb will do.
Think of a carb as a necessary restriction and like all restrictions you want the least you need.