how to feed twin 800cfm carb?
 

how many gph fuel pump do i have to use

I would use an electric pump that is fuel cooled[fuel goes through the motor ] they are more reliable, use a high pressure model with 1/2" line then have a fuel pressure regulator at the carbs to cut the pressure down to say 7 psi, a return line back to the tank from the regulator would work well, a setup like this should feed 800 HP , something around 120 GPH would be nice