MS3X Dual Fuel pump control

[5.3LS10]

I have a MS3 with the MS3X expansion card controlling a turbo LQ4 6.0 with a T56 in a foxbody. Car currently has a single Walbro 255lph pump and since we now added the turbo we need to increase the fuel supply. The 255 is an external inline pump and fuel cell has an additional -8 supply bung that can be used. Base pressure will be 58psi and a 1:1 regulator is used at the engine. Intake pressure levels are expected to be 12-18psi (only the dyno will tell). Quick cheap option is to add a second 255 to meet the fuel volume demands. HP goal is around 600-700hp. Already have a 1/2 line feed the car so was thinking about add a y block between my existing 255 and the 1/2 line. I know 2 of these pumps in parallel should more than handle the fuel supply but I have a few questions.
Should I run both pumps all the time?
Should I run one pump as main and have the other one come on after a certain amount of manifold pressure? Should be able to do this in the Advanced -> IO section
What will happen to the pressurized fuel leaving fuel pump A. Will it flow backwards through the y adapter through fuel pump B when it is not running?

Thanks
Shane

[nathaninwa]

I ran an ide focal setup to fuel my 2j. 255 primary and an 044 Y'd in. No troubles back feeding the 044, and had it turn on with tps rather than map so everything could be upto speed before actually needed. You can program the output to run for about 2 seconds with a key cycle too, but it's also nice to be able to tap the throttle and hear the pump while testing and things like that

[TheSilverBuick]

I run a staged pump through the simple ON/OFF outputs based on rpm and TPS so like nathaninwa says the fuel is already flowing by the time the engine needs it. On mine, the RPM is more conservative than the TPS. I have the second pump come on at 3,000rpm figuring if I'm holding a gear or cruising at a higher rpm, then I am likely to mash the throttle at any second and I want the fuel system ready. If I mash the throttle below 3,000rpm, the single pump can easily handle the fuel requirements of the engine below 3,000rpm so as the second pump comes on via TPS, by the time it crests 3,000rpm the second pump is on and ready with the extra fuel. My single pump is good to around 4,500rpm so my "safety" window is 1,500rpm wide so to speak.

I don't let the second pump shut off until below 2,000rpm though, and no minimum on the TPS because its a manual trans and shifting will see various points of low throttle and I don't want the pump to kick off between gears if I short shift it because of traction, etc.