For around 20psi for the second pump to kick on. Second pump wired right from the battery with hobhobs switch controlling the relay. Will be the cheapest option. Unless you've already got the ash controller. Also might want to think about using a bulk head on the top of the tank to get rid of the 5/16 fitting that is on there stock. And upgrading to larger fuel lines. I do not know the flow capibility of stock but for my piece of mind I have upgraded to braided stainless lines. -10 from the tank to the filter and -8 to the fuel rails then -6 as a return.