EFI advantages:
1. the FI manifold can includes shapes and volumes that will not suspend fuel droplets and would cause fuel distribution issues with a carburetor. Sometimes this is worth some power, but it depends on the manifold design. Example: Ford 5.0, where the air from the TB reverses direction in the plenum.
2. the FI throttle disc(s) area can be greater than a carburetor because engine vacuum does not actually pull fuel from the bowl, and will work below .25 Hg". This gives a slight improvement in pumping loss - but only if you use a system larger than your carburetor. 4 bbl. carburetors are normally calibrated for engines that can pull 1.5 Hg" at WOT. Carburetors rated by CFM are fictional: "600CFM" means it will flow 600 CFM at 1.5 Hg" on an engine that flows 600 CFM. If the engine is bigger, it will flow more than 600 because it will pull higher than 1.5 vacuum. If the engine is smaller, vacuum will drop and the carb will flow less than 600. For a V8* the usual calculation for CFM, where:
D = displacement in inches
RPM = engine speed at peak power
VE = efficiency, less than 100% in anything but a race engine
CFM = D X RPM X VE / 3,456
Example: 298", 5,500 RPM, 95% (excellent) VE
CFM = 298 X 5,500 X .95 / 3,456 = 451
Conclusion: 600 is already too big
* the intake characteristics of engines with less than 7 cylinders are quite different than a V8. The CFM capacity for a 6 cylinder has been estimated at 10% higher than a V8, 4 or less cylinders even higher.
