Working on wing tanks for my RV-4.

Pickup lines are spec'd at -6 (3/8") in Van's plans.

Looking at a Walbro pump I replaced in my (Rusty's) RV-3B the inlet appear to be -6 but outlet is -4 (1/4") (fitting thread size -- so may actually be less).

Rusty carried -6 all the way to fuel injection rail and back to fuel regulator, but -4 back to tank from fuel regulator.

Also appears he used -4 from left wing to right wing fuel transfer. I'm using a 40105 Facet pump as transfer pump which appears to have 1/8"-27 INT fittings. It does seem to pump less than 30 GPH, but is pumping into same line as pressure regulator return line to tank. In the RV-4 I intend to have separate fittings in the right tank for fuel return and for transfer from left tank.

So the question is: is there any valid reason to have more than -4 lines after transfer pump and after high pressure pumps and filters going to the engine (and back). Higher power draw by pumps because of pumping into -4 lines instead of -6?

Obviously it'd be easier, less weight and less $ to use - 4 lines.

Finn

P.S. I think Tracy is running from the left tank, but I think advantage of running from the right tank is keep lines on the "cool" side of the engine. Probably minor.