Not much over stock. Actually, you may take a slight loss. EfI fires directly into the cylinders and does not allow for any pooling of fuel. As such, it is a more efficent burn. With the carb and intake, there is a less direct fuel delivery, and the fuel is already heated. Unless you plan to modify beyond the intake and carb, you may want to just leave it EFI. Unless you plan to make it an all retro engine.