Fuel pressure drop

I never really noticed my fuel pressure drop until this year after some changes to my engine. I set my dead head Quickfuel regulator to 6 psi and it drops to 3 during a full throttle run through the gears. My car pulls hard at the stripe 6200 RPM 124 MPH and doesn't nose over so I think I have enough volume.
What is an acceptable drop

Gus

What model pump.....

I'm still old school running a Carter high pressure race pump with -10 to the pump and 1/2" aluminum line to the reg. The car runs perfect I was just looking at the gauges closely with the new cam and intake to make sure everything was cool. It's making more power in the mid-upper range now with the new combo.
Pump is rated at 100GPH / 380 Lph 9-16 psi. 3/8" in and outlet.
Gus

Pressure is not a good way to think you have enough volume, instead jet it up at the track to see if you can slow the MPH down in the 1/4 mile
I know a NOS racer that had enough fuel volume to run 913 to 9.16 at 147. 3 to 147.8 MPH., he changed the jets from 80 in the fronts with a power valve and 90 in the rear with no power valve in two size increments up to 90 in the front and 100 in the back the same night within 5 hours and it didn't change the MPH at all It ended up slowing down the 60 ft. times, the 660 and 1000 ft. times but not the 1/4 mile ET and MPH enough to be noticeable
He added another fuel pump and line on the car, he ran the NOS on the old Holley pump and switch the carb to the new BG280 pump and ended up running 8.80s at 151+ MPH with the carb jetted up to 82 and 92 the next weekend with very similar D.A.
BTW, he had fuel pressure on both weekends, his needles and seats where holding the car back at low pressures
I've had the same thing happen on one of my cars when I ASSUME that the new Holley Dominator would have the same size needles and seats in it from the factory, WRONG
It had a .120 in the front with a .110 in the rear, I had added jet extensions and jetted the carb up but the MPH wouldn't hardly change in the 1/4 mile but it was slowing down from the 60ft. clocks all the way to the 1000 ft. clocks but not at the 1/4 mile clocks
I change the rear needle and seat to .120 and then it responded like it should have I hate Murphy
He does teach me to be more thorough though

It’s time for a flow test.......

Put a ball valve on the end of the line that feeds the carb....... a line attached to the valve going to a fuel container.
Turn on the pump and adjust the valve so the pressure gauge reads the minimum pressure you’d be satisfied with running....... leave the valve set like that.
Shut pump off.

Using some sort of container that you can fairly accurately measure a gallon with........ turn the pump on and time how long it takes to pump the gallon......... then calculate the gph flow at the observed/desired pressure.
Use the estimated HP from your 1/4 mile runs to determine the fuel requirement...... and see if the pump meets that requirement.

A 650hp motor needs about 54gph, at the desired pressure........ so just about a gallon a minute.
I like to see the pressure not drop below 4psi.

The pumps free flow ratings tell you nothing useful.

Thanks Dwayne it's time to drain the fuel for the winter anyway so I can check my volume then.
Gus

Sounds like that pump isn't doing the job, even though it should be able to. How is the voltage AT THE PUMP during the run? Hard to tell for sure but look over your wiring and ground and make sure you have eliminated any line loss. I assume you run an alternater? If everything is ok and the voltage is 14 v at the traps, then i would do what Herb McCandeless told me to do. Tape a dollar to that thing, throw it in a ditch, and say i lost a dollar in that ditch!

I had a Magnafuel 270 pump on my old pump gas Duster that I couldn't jet up the six pack enough to slow it down in the 1/4 mile so I bought a Magnafuel 300 pump to replace the 270.
I flow tested the 270 with all three fuel lines into a 5 gallon plastic pail three times for 11 seconds, it flow within 3 ounces on all three test, I then replace that pump with the 300 and reflow it three times, it flowed exactly the same amount as the 275
I called Magnafuel and told them what and how I did the two tests and they told me by allowing the fuel to flow out of the lines with no restriction I wasn't loading either pump to its full capacity, They said to put restrictors in the lines and retest the pumps. I hook one line to a carb and that stupid(300 pump) flow almost 50 % more out of two lines
I ended up finding that I had screwed up the system by using a BG 500 10 micron fuel filter between the pump and the tank, I didn't know that all paper element fuel filters are rated at 10 microns
Many ,many gremlins out there
Have fun Gus, let us know what you learn and find