If unrestricted with the same size opening outlet on both tests the higher pressure should flow more volume. I had a eye opening expereince several years back on unrestricted being less GPM than having a restriction in the fuel flow line I had swapped my Magnafuel 275 pump for a Magnafuel 300 pump do to running out of fuel according to my widenban, I had conducted both tests with the regulator set at 7.5 lbs on my six pak Duster motor, I flowed all three lines into a bucket for 20 seconds on both pumps, negligable differences in volume I called Magnafuel and they said to add a restrictor into the lines so the 300 pump would have more resistance and that would increase the volume It did, I hooked up one of the carb.lines to one carb and that dang 300 pump almost double the volume on the next tests through two #6 AN lines instead of three Lots of gremlins out there, I ended up finding out the large pumps like both Magnfuels don't like a fine(less than 80 microns) pre pump fuel filter in the line. I ended up removing the 10 micron fuel filter between the pump and the gas tank and put in a 80 micron prefilter there and moved the 10 micron filter between the pump and the regulator That works slick IHTHs