I agree with Bruce on this one!
A 600 hp TRANS AM engine can run forever with a
single Holley BLUE pump and the small regulator
that goes with the system. This is because a Trans Am car has a average acceleration curve off
Idle and the pump is able to keep the bowls filled everytime the driver is off the gas in a turn.
A DRAG car is at WOT from the time it leaves the line, it needs a massive amount of fuel immediately (along with high pressure to overcome initial acceleration forces (as Bruce said), and
has a hard time getting enough fuel through a two
bowl - two needle and seat fuel system.
Some of my math:
600 hp engine (.5 lb fuel per horsepower hr) will
require 300 lb fuel in an hour.
300 divided by 60 = 5 lb per minute (not quite 1
gallon per minute).
You noticed how the fuel flow dropped off as the pressure in your system went up, by 25% in just 4 psi change. In order to have the fuel move forward at a 1 lb per minute rate on a drag car you may need 20 psi to push the fuel forward or more. Most people also run a 1/2 fuel line to the front of the car which makes it even harder for the pump to overcome the slug of fuel wanting to go to the rear of the vehicle on acceleration.
This is why a BIG fuel system can sometimes be
worth 3 tenths on a 10 second car without showing
any lose in fuel pressure on the gauge with the
smaller fuel system.
The pressure in the line at the carb was dampened
buy the line length but there was a big hole in
the fuel delivery volume when the car left. You
typically do not see the "Hole" (lack of fuel) as
the bowl is vented to the air. The bowl fuel level
just drops due to the lack of fuel volume at the
needle and seat and the mixture goes leaner.
Hope this helps.
Tom V.
