fuel pump push pull question school me

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bbrroowwnn

bbrroowwnn

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I know EFI fuel pumps are usally in the tanks to push the fuel......Whereas the mechanical pumps on the motor will suck fuel from the tank.....I am running a carberated motor but want to run an electric pump.....My fuel cell has top outlet and was going to use a red Holley Electric pump.....They state the electric holley pumps are designed to push fuel, not pull fuel....However, it states it will pull fuel from the top of the cell once a siphon effect is created.....Is anyone currently running this way and are you having any fuel starvation problems at WOT?.....My question is do they make an electric fuel pump designed to suck fuel from the top of the fuel tank? If so, what kind am I looking for?
 
.............Some ppl use them that way, not the best idea....cause u can have fuel problems......way better to have the pump lower than the cell so it gravity feeds from the bottom of it.........mech pumps were put on the engine for cost and simplicity.........kim.............
 
oldkimmer said:
.............Some ppl use them that way, not the best idea....cause u can have fuel problems......way better to have the pump lower than the cell so it gravity feeds from the bottom of it.........mech pumps were put on the engine for cost and simplicity.........kim.............
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I have the pump lower than the cell but the cell has the fittings on the top....My question is ; Is there an electric pump that is designed to suck fuel from the top of a tank like a OEM application? Turbine style?
 
The top fittings are for return and venting lines, not for outlet. I know of no external electric pump that is designed to suck fuel from the tank (especially without an internal line that goes into the fuel). While all pumps have some suction head to them these pumps are designed to have a gravity flooded inlet and push out to the carb.
 
If you really wanna get technical and split hairs.....which I just LOVE to do....LOL, all fuel pumps really pull since they have an inlet. What they mean by "PUSH" instead of "PULL" is the actual location of the pump. With the pump as close to the tank as possible, it is considered to be pushing the fuel since the majority of the fuel system is in FRONT of the pump. Conversely, an inline mounted pump somewhere in the middle of the vehicle or even under the hood is considered a puller, since there is a lot of fuel line between it and the tank. But, all pumps PULL fuel out of the tank.....there's just no getting around that fact, no matter how you slice it. I've used Holley black, red and blue pumps mounted close to the tank or cell with no problems regarding fuel pickup or starvation.
 
stumper said:
The top fittings are for return and venting lines, not for outlet. I know of no external electric pump that is designed to suck fuel from the tank (especially without an internal line that goes into the fuel). While all pumps have some suction head to them these pumps are designed to have a gravity flooded inlet and push out to the carb.
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Well said.....but there are some cells with top fittings for outlets that have siphon lines which run to the bottom of the cell. In either case, you're dead on the money. Fuel HAS to be drawn from the bottom of the tank somehow. If you don't think a Holley red pump will suck fuel out of a tank or cell with a top mounted outlet with a siphon tube going to the bottom of the tank, you should try it sometime. LOL
 
He probably has a tank like this. No low outlets, all outlets/returns come out the top. More of a street rod style tank, not a drag racing.sump oriented set up.

$(KGrHqMOKjEE330-cM!bBODS0y)6-Q~~_1.JPG


The pump should be able to pull from the tank. It's just not the ideal situation.
 
In PRACTICAL terms, unless you are running some 800 hp monster, most "street" pumps are DESIGNED for some amount of suction. In general terms, the CLOSER you get to the tank, the larger and less restricted you make the suction line (larger diameter, free flowing or no screens or filters, and a minimum of elbows) this helps to DROP the suction restriction pressure, which you can actually MEASURE with the proper gauges. A good quality vacuum gauge is probably all you really need.

The analogy is a water well pump. The old "shallow" pumps can only "suck" so far, so "back then" they put a water jet at the bottom to boost it, and finally, moved the pump right to the bottom of the well.

It matters not what kind of fan/ blower/ pump you are using, more push and less "pull" is what you want.

So, without causing a danger from damage or collision, mount the pump as low and as far to the rear as you can.

By the way, SOMEPLACE I even read an article once about outlet line size. The allegation was --specifically so far as drag racing--that an outlet tube that got "too large" held enough weight (mass) of fuel (the length of the car) that under hard acceleration this acted as "false head pressure" against which the pump had to work.

I haven't calculated the fuel mass in say, no 10 tube for 8 or 10 feet or whatever, so donnooooo

Another article was speaking of the popular motor drive, internal bypass pumps, and the idea was that when in bypass (idle, light cruise) under low-flow conditions, they may be their own enemy, the impeller churning up and heating the fuel, adding to possible vapor lock problems.

This does make some sense, and is an argument FOR a vapor return (orifice) system / or a front mount, external bypass regulator.

This alleged problem is one that mechanical pumps don't have, nor do the old "pulser" pumps of my day---they simply stopped pumping when pressure built up.
 
StrokerScamp said:
Well said.....but there are some cells with top fittings for outlets that have siphon lines which run to the bottom of the cell. In either case, you're dead on the money. Fuel HAS to be drawn from the bottom of the tank somehow. If you don't think a Holley red pump will suck fuel out of a tank or cell with a top mounted outlet with a siphon tube going to the bottom of the tank, you should try it sometime. LOL
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Yes, mine has one vent on top and one outlet on top that has the hose inside going tot he bottom of the cell.....
So stroker, you have used all three holley pumps on a cell sucking from the top????
I have it mounted below the cell and about 1 foot in front of it....so it is pushing most of the way to the carb.....
 
crackedback said:
He probably has a tank like this. No low outlets, all outlets/returns come out the top. More of a street rod style tank, not a drag racing.sump oriented set up.

$%28KGrHqMOKjEE330-cM%21bBODS0y%296-Q%7E%7E_1.JPG


The pump should be able to pull from the tank. It's just not the ideal situation.
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Yes, it is similar.....there is no 2" sump in the bottom.....no fittings on the bottom.....just a vent fitting on the top and another fitting on the top which has a hose inside that goes to the bottom of the tank.....
 
Bigger lines; we were told by Dan Dvorack that bigger=head pressure. While we were talking, he had his last Lawman, 64 Beledere, hemi, on a lift; it had 3/8 braided. But Dan starts talking faster when he sees you eye-balling his old secrets, dunno.

On the 440, he said use the 5/16".
 
bbrroowwnn said:
Yes, mine has one vent on top and one outlet on top that has the hose inside going tot he bottom of the cell.....
So stroker, you have used all three holley pumps on a cell sucking from the top????
I have it mounted below the cell and about 1 foot in front of it....so it is pushing most of the way to the carb.....
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I have run the blue and red pumps before on cells like yours, yes.
 
StrokerScamp said:
I have run the blue and red pumps before on cells like yours, yes.
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Ok, I will proceed with what I have then.....I have one of those see-through clear filters up by the carb and it is about half full at start up but after running it about 20 minutes in the garage , it is near empty....Just barely seeing fuel sputtering in the bottom......Although the motor hasn't stalled or stumbled.......As you can tell from my pics, It is going to be awhile until I can actually get it on the road and see what it does....I was just trying to save myself a headache down the road......
 
Even with a standard tank, the fuel is sucked up high before dropping down to the pump since the highest point is near the highest part of the trunk floor. The fact that your tube enters thru the top of the tank is irrelevant. What matters is how high your fuel tube goes. It seems like you run it up much higher than required. Why not put a 90 deg elbow right off the top fitting to keep the tubing lower?

Re how high could the tube go? If the pump could draw a perfect vacuum (unlikely), it would be limited to a certain height by physics, which varies with fluid density. That is why mercury is used in traditional barometers, since a water column would go to the next floor up.

Re diameter of the fuel line, there are trade-offs. A larger diameter gives less flow drop, but if too large it lessens the siphon effect. Someone mentioned the weight of fluid causing a slosh-back under acceleration. Most carbureted engines were designed with 5/16" tube, so probably sufficient. High-pressure EFI pumps bypass fuel around the engine so higher flow, though the latest vehicles must bypass within the tank (1-way trip to engine, EPA mandate). The current Corvette has a 3/8" line, but not sure that was required.
 
Hello again, Reviving this thread again.....I have since put a 90 degree fitting right on the top of the fuel cell so it doesn't have to siphon as high...... I have a new fuel cell in the car with a new inline filter then a new holley electric fuel pump then another new inline filter near the Thermoquad that is clear so I can see the fuel....The fuel filter only gets about 1/4 filled no matter how long I leave the fuel pump run before I start it....The car starts and runs great for a few minutes , great throttle response, but then the fuel in the clear filter slowly dwindles down to very little or nothing within about 10 or 15 minutes or so then it stalls....I have a vent line on my gas tank which I just have a rubber hose on open to the air in the rear of the vehicle.....My question is this, I have the 73 model year TQ and I have the two ports on the carb that normally went to the charcoal cannister plugged off.....was wondering because I looked at my original 73 dart sport with TQ and besides these two lines going to the charcoal cannister, it has 1/4 line going back to the gas tank.....So I am thinking that my problem of the fuel not getting to the carb is because there is no way for the carb to vent....Is this possible and reasonable thinking? If so, would it be OK to run a return line from one of these two ports on the carb back to my vent line on the tank? thanks Paul
 
Sounds reasonable. My 60's carbs have a vent on the top of the bowl, with a lever that opens a rubber disk to vent at idle. Later ones ran the vent to a top tube (to charcoal cannister), but have a similar valve that opens at idle. Before you go to the trouble of running a new tube, try just unplugging your vent. It won't spew gas unless the bowl overflows, and an old 60's carb would flow it out the vent too. Instead of a tube, maybe put a little air filter on it (to keep out bugs) and run a plastic hose below the engine in case of overflows. My M-B's have those on the vacuum vent lines. Look in the bubble packs at auto parts.
 
I uncapped the bowl vent that I had plugged that normally went to the charcoal cannister and it stays 3/4 filled all the time now.....So it must have needed the vent open to work as a bleeder for air to escape so fuel can come into the carburetor better....problem seems to be solved
 
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