Choosing a Mechanical Fuel Pump

[AntRant]

I'v decided to go with the Mechanical fuel pump but wich one? How much GPH do i need? Which psi should i run? Edelbrock said don't go over 6psi, Holly said 6.5-7psi. I currently run a mostly stock 460 w/600cfm Holly double pumper(750cfm somewere down the lake)I'm so lost on this topic so if any body can help PLEASE DO SO............p.s. I'd like to stay away from running a return fuel line......... Thanks

[temporary name]

i just happen to be reading this when i saw your post maybe of some help.http://www.centuryperformance.com/fuel.asp

[Infomaniac]

A 6 check valve holley or Edelbrock at 6 psi is more than enough. I have run 600 HP 1,000 CFM carbed engines no problem with one. Be sure to check the float bowl level after installing the new pump.
Also, I prefer to filter the fuel after the pump. A partially clogged filter has less effect on fuel flow when installed in the pressure side. You should run a coarse screen of some type before the pump to keep the big chunks out.

[AntRant]

Temporary name, What do they mean by "H.P. per hour" for that fomula?

[temporary name]

in that formula they are changing the average .5 pounds per 1 hour into gallons per hour. the formula could also be written
hp x .5 x .167 = gph

[Costello]

I'm no professional engine builder or tuner, basically just a hack, but that formula would only require 41.75 gph for an engine producing 500 hp. I didn't read the article yet, maybe that's the actual consumption of fuel, but I know for sure you nee a pump producing much more flow than that to adequately supply an engine making 500 hp.

[LVjetboy]

Costello,
A couple of things to consider. Pump rated flow is usually stated at 0 psi, so the flow at 6 psi will be less. For example, the Mallory 110 is rated at 110 gph but at 6 psi flows 95 gph.
Secondly, urban legend (and fuel pump marketing) claims bigger is better. My guess...most people oversize their fuel pumps. 42 gph for 500 hp should be close, believe it or not. Just for example, I have a dyno sheet for a blower motor output of 843 hp burning 458 lb/hr of fuel (measured). 458 lb/hr = 76 gph. And for 843 hp, the above fuel equation calculates 70 gph...not far off from actual dyno sheet measurements, and able to be supplied by the lowly Mallory 110 at 6 psi. Would I use a 110 on a 850 hp engine? No. Because that engine would be bumping the pump's design limit. But on a 500 hp or less engine? The 110 is well within design limits. And on AntRants mostly stock 460? The 110 is overkill.
AntRant,
For your engine, I'd shoot for 6 or 6.5 psi and a rated flow of 80 or 110 gph at the most (in case of future engine upgrades) If you go high on fuel pressure (7 or 7+) you're asking for needle valve leaks and flooding problems.
Finally, are you sure you want mechanical? Mechanicals can be reliable, but they're slow to prime on the first start (longer engine cranking) and lack the security of a hidden cutout switch when you park overnight. Just some thoughts...
jer

[AntRant]

LVjetboy, Changed my mind i'm gona use a Carter electric pump. A street rod friend convinced me....

[LVjetboy]

I think you'll be happy with the Carter. I used those on both my first jet and my firebird and they worked well.
jer

[Costello]

I'm with you LV. What I was saying is with the engine you listed consuming 70 in the equation and 76 gph on the dyno sheets, we don't select a pump equal to that number. Even at 6 psi and around 95 gph, you have some cushion there between actual consumption and pump rating. Thanks.

[LVjetboy]

Good point Costello. Although I haven't seen a hard number, I would double the required flow (calculated by HP/12) to equal pump design limit at psi. This gives cushion for fuel filter and line restrictions...etc. The Carter flows 72 GPH @ 7 psi, so should be good to 450 hp with cushion.
Just as a point of interest (and to test my new picture hosting service http://free.***boat.net/ubb/smile.gif here's a chart with dyno data (compliments of MikeW) and Mallory fuel pump design limits:
http://users.lvcm.com/lvjetboy/FuelFlow.jpg
Hope the picture works
jer