On EFI applications the return fuel is under little to no pressure compared to the supply so it can tolerate a smaller line. I wouldn't push my luck though on a 1/4" line though.
EDIT - Also, with some EFI setups you can PWM control the pump so you may have very little return flow so that makes running a smaller line way more feasible.
AG.
Correct. If the EFI pump is sized correctly then the return line should not have much pressure in it so it can be smaller. All the EFI cars that I've plumbed lately have used a regulator in the trunk (race cars) or the regulator is in the tank (street cars) so I don't use a return line anymore. The OEM guys don't use return lines.
