fuel pump help

[Sir_Loin]

ok so my z has a 350 crate engine with a 750 carb and my fuel pump went out on me and I didnt do the swap myself plus the car wasnt running great with the old one anyway so I need to pick a completly new one, but im not sure what gph or psi it should be able to make, help appreciated, btw my engine does about 250 at the wheels

[grumpyvette]

do you intend to replace it with a mechanical or electric replacement pump?

do you have a fuel pressure regulator and return line?

 

Holley 12-327-11 $75 PUMP

Holley 12-803BP $67.39 regulator

 

 

 

 

http://store.summitracing.com/partdetail.asp?autofilter=1&part=HLY%2D12%2D327%2D11&N=700+115&autoview=sku

 

http://store.summitracing.com/partdetail.asp?part=MRG-1561

 

http://store.summitracing.com/partdetail.asp?autofilter=1&part=HLY%2D12%2D803BP&N=700+115&autoview=sku

 

if you want a steady and fully adjustable pressure fuel flow youll need a return line style regulator and a decent pump in the 80-140 gph range matched to the correct sized fuel lines

 

http://www.centuryperformance.com/fuelish-tendencies-understanding-fuel-pressure-and-volume-spg-140.html

 

theres a good deal of usefull info in this link above

do the job correctly the first time and avoid the problems and guess work and testing ,cheap auto store replacement stock pumps usually get you envolved with

[Sir_Loin]

electric external, no regulator, no return line

[naviathan]

ok so my z has a 350 crate engine with a 750 carb and my fuel pump went out on me and I didnt do the swap myself plus the car wasnt running great with the old one anyway so I need to pick a completly new one, but im not sure what gph or psi it should be able to make, help appreciated, btw my engine does about 250 at the wheels

I think I just went cross eyed trying to read that giant run-on sentence...

 

This gets my vote for Run-On of the Week!

[grumpyvette]

DO YOURSELF A BIG FAVOR and don,t slap the cheapest P.O.S stock replacement type pump into the car with no return line or regulator and no fuel pressure gauge,...... youll be FAR better off with a RETURN LINE and FUEL PRESSURE REGULATOR installed and a fuel pressure gauge so you can instantly adjust and check your fuel pressure, even if you use a electric fuel pump, keep in mind electric fuel pumps PUSH fuel far more efficiently than they PULL fuel and electric pumps use the fuel FLOWING THRU them as a COOLANT, so mount the pump as close to the lower surface level of the fuel tank and as far to the rear of the car, inside the frame rails as you can.

 

http://store.summitracing.com/partdetail.asp?autofilter=1&part=CRT%2DP4594&N=700+115&autoview=sku

 

 

ADEQUATE (for your current set up)

http://store.summitracing.com/partdetail.asp?autofilter=1&part=CRT%2DP4601HP&N=700+115&autoview=sku

 

 

OR

 

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2DG3136%2D2&N=700+115&autoview=sku

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2DG3136%2D2&N=700+115&autoview=sku

 

BETTER

(and YEAH ID SURE INSTALL a return line,regulator and fuel pressure gauge)

[grumpyvette]

IF you have not yet done so, take the time and effort to read thru these whole links,

 

http://www.centuryperformance.com/fuelish-tendencies-understanding-fuel-pressure-and-volume-spg-140.html

 

http://www.fuel-pumps.net/fuelpumpsfaq2.html#2

 

 

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 theres a voluum of fuel past the valve with enought pressure to allow BOTH the SPRING and the fuel pressure past the valve to close the valve untill the fuel is reduced to the point that the SPRING and the remaining fuel pressure/voluum beyond the valve can not hold the valve closed and the valve is force open and held open untill, that diffearance 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 enertia, 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, untill 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 voluum 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 youll 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 bye-pass regulator functions in a totally differant manor

assuming the same set-up but you replace the regulator with a bye-pass style regulator, the bye-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,youve 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 potenially 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 to 5.5 psi or less the valve to the bye pass line will close but thats 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 CONSISTANTLY

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

should some crud get stuck in the valve and it cant close NOT MUCH HAPPENDS, because its normally OPEN not closed

if you check youll see MOST EFI systems are BYE-PASS regulated designs also due to control and relieability 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 bye-pass style regulator also

 

[Sir_Loin]

thanks for the help