[WSSix]

Because with two in tank pumps the two pumps are pulling through separate lines. Adding an inline pump means it is pulling fuel through the other pump or simply boosting the fuel the other pump is supplying. It works but at the level you've built the car two, two in tank pumps is smarter.

Jody and gearheadsgarage are correct though, just take it easy at first and pay attention to the data log to know where your fuel is at. Data logging is real time so you can easily let off the throttle if it starts to go too lean and not hurt anything.

Check with Rick's and Racetronix. I think Racetronix had a setup that puts two intake pumps through the same sending unit. I know I've seen this setup somewhere. Essentially, it could allow you to simply drop a twin pump setup into your current tank and not modify anything major.

Oh and always remember that pressure is separate from flow volume. This is with any fluid and air is a fluid.