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  #1 (permalink)  
Old 06-05-2003, 05:47 AM
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Post Fuel pump question

I need a little help figuring this out folks. I'm building a '46 Chevy Panel truck with a SBC 350, mild cam, TH350 trans and a 650 cfm carb. I'm putting the fuel system in now and want to put an electric pump in the back near the tank and a mechanical on the block. What I need to know is what should I be looking at for GPM rates for these pumps??

Thanks for the help folks.

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Old 06-05-2003, 06:12 AM
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you need to run one(mechanical) or the other(electric) but not both style pumps. Something around 120 gph and 6 psi should do fine.

[ June 05, 2003: Message edited by: engineczar ]</p>
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Old 06-05-2003, 06:19 AM
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I'm not sure why you would want a mechanical pump on the engine but I would think that your electrical pump would only have to pump what ever the maximum GPM is that your mechanical pump can produce. My concern would be that the mechanical pump could build enough pressure on the inlet side of your mechanical pump to bust the diaphragm and fill the crank case with fuel. You should be able to get the maximum GPM on your mechanical pump from the manufacturer spec sheet. I hope this helps.
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Old 06-05-2003, 06:40 AM
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I run a Carter 5psi, street rotary fuel pump - Summit part #CRT-P4070, $57, pump - on all my cars. Haven't had a problem in 20 years. Can also get a 7psi unit, #CRT-P4594, also $57, but that extra pressure isn't needed on a street engine and will cause more problems that it will solve. Both flow 72gph, plenty for a warm 350.
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Old 06-05-2003, 11:29 AM
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Hey Willys:
How loud are those Carters? I would need to run 2 I think. I have 2 fuel tanks that are switched, I was thinking of switching fuel pumps as well. Originally the car had 2 fuel pumps but in the convertion they were taken out.

Regards
Mark
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Old 06-05-2003, 11:34 AM
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They are rotary pumps, not vibrating diphragm type so they are very quiet. Plus they come with a 100% rubber isolated mount so I never hear them running.
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Old 06-05-2003, 11:55 AM
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Nice price too. I went to summit and took a look but I couldn't get the diamentions of them off the web site. Oh yeah do you use a pressure switch or anything to shut it off in case of emergency?

Regards
Mark

[ June 05, 2003: Message edited by: Jag Daddy ]</p>
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Old 06-05-2003, 03:35 PM
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The thing is nice and compact - about the size of a big fist. No, I don't use a safety pressure switch - guess I should look into that.
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Old 06-06-2003, 07:31 AM
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My Bronco II had a inertia switch that was located in the passenger compartment of the truck on the passenger side. I haven't seen one for aftermarket pumps, I wonder if they are vehicle specific. The pressure switch looks like a viable option but hanging the pressure switch and the oil pressure sender off a tee seems like it would be a bit heavy on a brass fitting.

Regards
Mark

[ June 06, 2003: Message edited by: Jag Daddy ]

[ June 06, 2003: Message edited by: Jag Daddy ]</p>
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Old 06-06-2003, 07:56 AM
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Well, I do have a pressure switch on my Willys on the back of the oil gauge that turns off the ignition if pressure drops to 7psig. It is on a Tee on the back of my gauge and the switch is one of those long ones but hasn't seemed to cause any problems in 7 or 8 years. I guess I could work my fuel pump into this switch too. Thanks for the hint.
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Old 06-06-2003, 08:18 AM
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Only problem I can see with that willys is you won't get any fuel pressure at start up until you pass the 7 psi limit. You might have to rig in a wire off the starter solinoid wire so that you'll have pre-start voltage to the fuel pump so you can pressurize the system. Then have the pressure switch kick in as a safety switch. The other option would be a momentary switch that would supply power to the fuel pump long enough to presurize the system (maybe on the dash with a cool blinking LED)

Regards
Mark

[ June 06, 2003: Message edited by: Jag Daddy ]</p>
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Old 06-06-2003, 01:30 PM
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I like the inertia switch idea. My Ford has one, and it does seem to be tripped, although rarely, by small impacts (parking by ear, etc.). I think if I were using an electric pump, I would mount the switch somewhere I could reach it from the seat. It might be less sensitive, and easier to reset if necessary. I don't think they're vehicl-specific. Mine is just mounted to the rear trunk wall.
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Old 03-16-2004, 08:20 AM
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Quote:
Originally posted by Jag Daddy
Only problem I can see with that willys is you won't get any fuel pressure at start up until you pass the 7 psi limit. You might have to rig in a wire off the starter solinoid wire so that you'll have pre-start voltage to the fuel pump so you can pressurize the system. Then have the pressure switch kick in as a safety switch. The other option would be a momentary switch that would supply power to the fuel pump long enough to presurize the system (maybe on the dash with a cool blinking LED)

Regards
Mark

[ June 06, 2003: Message edited by: Jag Daddy ]</p>
Didn't notice this comment a year ago! I use an electical bypass of the pressure switch for startup. Never a problem.
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Old 03-16-2004, 08:43 AM
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I have a 350 Pontiac motor with an 670 cfm street avenger carb and am running holleys street avenger fuel pump (12-389-11). Flows @ 110 gph 6.5-8 psi and runs great! These mechanical fuel pumps are part of their dyno proven system and are not noisy either. Plus i like mechanical because if something were to happen the electric pump would still be pumpng out tons of gas as the mechanical would stop. Just something to think about.
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