If you did the test right....... then just under 22gph is what I get for 1qt in 41 seconds.

I assume you tapped into the system from the line that feeds the carb, installed a valve on the end of the line, turn on the pump and close down the valve to achieve 6psi system pressure.
Then time the flow.

I would try it at 5, 4, 3 psi as well, just to see how low the system pressure would have to be to flow the fuel you need (50-55gph).

My experience has been that when flowing the entire system, while maintaining the required system pressure....... you need something like a 140gph pump....... for your power level(600-650hp).

I have seen many systems not pass this test when fuel pumps that are marginally suitable are used.

The question now is, is it the pump...... or a restriction in the line/system?

Did you see what the free flow was?

I know of one instance where the free low was more than adequate, but when tested at 6si, there was barely a dribble coming through(about 6mins to fill a gallon can).

You just learned a lesson in fuel pump flow ratings, and how the rest of the system affects what’s actually available to the carb after all those fittings, the line, the regulator, etc.

Time for a bigger pump.
Get something that’s absolutely big enough.

Is what you have mounted in the tank now?

Question for you.......

I assume you’re using a return style regulator?

Is that in the back or up in the engine bay?

When you’re doing the pressure/flow test....... was fuel still returning to the tank?

If so, perhaps a different regulator might improve the situation.

My guess is the regulator can’t keep the pressure low enough (6psi), while maintaining a high flow rate to the carb, without still returning fuel to the tank....... fuel that really should be going to the carb.

I’d plug the return to the tank and redo the timed test with the valve and see how much extra flow you get from that.
BTW, what regulator are you using?

Your pump is supposed to be capable of 60-80psi right?

If plugging the return results in a significant increase in flow into the can while maintaining 6psi(you “should” have to open the ball valve farther to get the 6psi system pressure), then I would try running two regulators.

I’d have the first stage regulator(the return regulator) set to about 25-30psi, then run the outlet of that one into a dead head unit that can handle the 25-30psi inlet pressure, and set it to 6psi.
The MagnaFuel regulators are designed to operate at 25-30psi inlet pressure.

Basically, you want it so the return regulator shuts off the fuel going back to the tank when the demand is high, and I think you’ll have a better chance of accomplishing that if that part of the system remains fairly high pressure.

If plugging the return doesn’t result in a lot more flow into the can........ then it’s on to a new pump.

If the pump will keep up, you would basically be duplicating this(only it would have higher system pressure in the first stage than the one in the link).

https://www.aeromotiveinc.com/product/efi-2-carb-dual-fuel-pressure-regulator/

So what do you get for flow now with the ball valve adjusted to maintain 6psi?

In any case, what you’ve done should show up on the time slip..... and you should find the car pulls in high gear better than it ever did.

Hopefully the weather will be nice the next time the track nearer to you has some racing.