wpc
You should look up look up friction loss/100ft. Four 2in. pipes will not give you the equivalent of a 4in. pipe. You have to consider the gpm. For ex. a 100 foot run of 2in. @ 200gpm will net a pressure loss of approximately 25# in each of the 2in. pipes. A 4in. pipe will net a pressure loss of 1# in the line, this is due to the boundary friction, water that is in contact with the pipe. figures used here are for smooth pipe(copper). These are taken from the standard plumbing code.
