EFI cars use a boost referenced fuel pressure regulator, that adds fuel pressure in direct proportion to the boost pressure so the pressure across the fuel injector is always constant.
I my car the base fuel pressure is 43 psi, at 20 psi boost, the fuel rail pressure would be 63 psi gage, but the actual differential pressure across the fuel injector is still 43 psi.
Fuel flow varies at the square root of the pressure drop across the injector so even small boost pressure can lean you out without a boost referenced fuel pressure regulator.
If you are running a carburetor, many setups enclose the carb in a pressurized box so its air circuits see the same boost pressure as the manifold, or they use a draw through setup where the carb is upstream from the blower so both the fuel and air go through the blower. The fuel in that case helps cool and seal the blower on roots type blowers. On centrifugal blowers there is less advantage to the fuel cooling, but the heat of compression does ensure the fuel is completely atomized.
Larry
Larry