fuel flow related info

[grumpyvette]

http://www.koolfuel.com/information.htm

 

http://www.fuel-pumps.net/fuelpumpsfaq.html

 

http://www.magnafuel.com/support/index.htm

 

 

http://www.magnumforceracing.com/store4/magnaflow/fuel_system_technical_notes.htm

 

 

http://www.rceng.com/technical.htm#WORKSHEET

 

very good system

not quite as good, but still ok

[grumpyvette]

FUEL PRESSURE REGULATORS DEADHEAD vs BY-PASS STYLE

 

dead head regulators seldom allow a stable fuel system pressure, you NEED a by-pass style system with the regulator mounted close to the carb, you can ignore the nitrous part of this diagram if your not running nitrous but the concept of the higher pressure feed bleeding off excess pressure at the regulator so that the carb sees a constant feed pressure is valid. it may help if you understand the difference in concept of how the regulators work

 

PRESSURE IS THE MEASURE OF RESISTANCE TO FLOW

 

THE DEAD HEAD STYLE REGULATOR

Works with a spring on a valve that allows the valve to open once the DIFFERANCE IN PRESSURE between the sides of the regulator valves fuel lines has changed

Think of it as a door that has 7-10psi on the feed side and you want lets assume 5.5 psi at the carb

as the fuel pump fills the line it eventually (fractions of a second) reaches the point where there’s a volume of fuel past the valve with enough pressure to allow BOTH the SPRING and the fuel pressure past the valve to close the valve until the fuel is reduced to the point that the SPRING and the remaining fuel pressure/volume beyond the valve can not hold the valve closed and the valve is force open and held open until, that difference in pressure is restored. now lets launch the car hard, the pump that had maintained 8-10 psi to the regulator, 5.5 psi past the valve and the spring in the regulator is now fighting the fuel in the line feeding the regulators inertia, and the sudden drop in pressure as the throttle drops full open in the carb, what the pump sees is the full 8-10 psi or MORE the regulator sees a sudden drop off to near zero and it opens wide, if the fuel pumps able too it tends to flood the fuel bowl for a second then the valve slams shut, until the pressure drops off as you hit each gear the cycle repeats, the result is a surge in pressure and a rapid drop off in volume then a rapid flood of fuel that rapidly cycles as you go down the track

if you had a accurate fuel pressure sensor at the carb you’ll see a rapidly cycling pressure/flow

if some crud gets stuck in the valve it cant close and your carb FLOODS OUT, because it must fully close every few fractions of a second to work correctly

 

the by-pass regulator functions in a totally different manor

Assuming the same set-up but you replace the regulator with a by-pass style regulator, the by-pass regulator works by opening a valve too a much lower pressure path for the fuel to return to the tank, the open fuel return line. Anytime the pressure exceeds the 5.5 psi, you’ve set it to, so the fuel line to the carb can only see a max at that 5.5 psi. now the pumps sitting there potentially supplying at 8-10psi just like before, but it can never exceed 5.5 psi because the bye pass regulator bleeds of any excess the pump supplies. but lets look at your launch, if the pressure drops to 6, 07 psi nothing changes at the carb, it it increases to 10 or 12 psi, nothing changes at the carb ,if it drops to 5.5 psi or less the valve to the bye pass line will close but that’s seldom a problem, it the sudden changes in pressure and over pressures that happen when you suddenly change the fuel flow required or the (G)loads on the system that potentially screw things up, the bye-pass regulator style regulator isolates the carb and maintains the desired 5.5 psi FAR MORE COBNSISTANTLY

Now let’s assume the spring get weak over time or the adjustment gets set at 4 psi in error, with the bye-pass style you’ll probably never notice, if you had a accurate fuel pressure sensor at the carb you’ll see a rock steady pressure/flow

Should some crud get stuck in the valve and it can’t close NOT MUCH HAPPENDS, because its normally OPEN not closed

If you check you’ll see MOST EFI systems are BYE-PASS regulated designs also due to control and reliability issues

 

But on the dead head the cycle just gets about 20% more erratic and more frequent in the cycles, further weakening the spring over time

 

 

 

btw your fuel pump tends to run under less stress and run cooler with a by-pass style regulator also

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if you can,t smoke the tires from a 60mph rolling start your engine needs more work!