Mechanical fuel pump and electric pump. ?
 

Can operating an electric fuel pump near the tank simultaneously with the

Mechanical pump damage the mechanical pump ?


Thank you.

Why are you running both?
It’s very hard for a mechanical pump to suck thru a electric one, especially if the electric one is not gravity fed real well!

Tell me about it. When I bought my LeMans the previous owner had a cheap Mr. Gasket pusher pump installed back by the tank, above fuel level in the tank, that was in addition to the mechanical pump. That thing acted as a restriction if anything. Pulled the POS out and haven’t had an issue since.
Mount it lower than tank level or buy a pump that will lift fuel.

I run check valves so the mechanical pump is able to pull full flow and bypass the electric. I turn on the electric as a helper pump for full power at the strip (just under 600HP on a couple cars) or to prime the carb. It is off most of the time. Carter sells an electric pump kit with the check valves, it was designed to run in tandem with the mechanical pump.

I have been running a pusher at the tank through #8 hose to a factory mech pump for 25 years.Electric is on a switch under the dash,run it when racing and for priming.NO issue pulling from the pusher with a pair of 750 NASCAR AFBs.FWIW,Tom

Is there a reason you don't move strictly to an electric pump in general?

The best setup in my opinion is to use an in-tank pump, in a new EFI ready tank that has an internal sump. Then use a bypass regulator to run the 5-7psi to your carb that it requires. You can even plumb that so it takes advantage of the stock line from the mechanical pump to the carb. Unless you're specifically looking for the mechanical pump to be in place, nobody would be the wiser.

It's a bit more funds, but it's not that much more work than plumbing the electric pusher. It's the best reliability play though.

I have had that same set up for decades as well. Small pump on the frame rail looks like a fuel filter with a couple wires coming out of it. Something like 4 PSI.

Mine is a Holley,dont remember what one.Tom

Pretty much as JLmounce said, electric in the tank is the way to go if you've got a thirsty engine making some power.
It's clean, simple, and reliable and has the ability to support bigger power in the future if setup properly. It's also very quiet :)
Only real draw back is cost.

I have run an Electric Fuel Pump, at the tank for many years.
First a Holley "Red Pump". Then a Holley "Blue Pump". (Both had vane sticking issues).

Went with a Carter 4603 electric fuel pump and a By-Pass Circuit some years later.
Very dependable. E-pump was off unless priming carbs or "acceleration runs on the street". Fuel went thru the by-pass to the mechanical fuel pump.

Then I stepped up when Tanks,inc first came out with the in-tank pumps.

255 liter/hr normal installation with a good FP regulator.

Later went to a 400 liter/hr pump in the tank.

System in the car now is TWO EFI 450 liter pumps on a special fuel pump "dual mount cover" The latest EFI pumps are alcohol tolerant. Only one pump is used at a time, the other pump is a Back-up pump when I go on trips to the bridge.

The dual fuel pump mount (made in the Chicago area) required fuel tank mods to put
both 450 pumps in the tank. The tank is a aftermarket (Tanks,inc tank).

Very sweet system and the fuel with be there if I reinstall a vortech supercharger on the car: YSI (1200 HP Unit).

Tom V.

Spend the money on a good fuel system.

We did it for years and years never an issue

Ran a Conelec pump on 421 GP back in the 70s with mechanical pump. Then took same pump put on my SD. Lasted till about 8 yrs ago, pump finally gave out. Only used electric at the strip or on street for maximum fuel delivery. As car would shut off in 2nd when hot without. Now bought a Robb Mc high volume mechanical pump, 500hp. Havent got it mounted as it is little physically different,close though.

I just help someone that had a pump similar to that Mr Gasket electric pump in series with the stock pump, a few weeks ago on a OHC tempest. It wasn’t working very well and was flooding out occasionally. It has the pump similar to the Mr Gasket, I call them chatter pumps. I think they are diaphragm operated. They are usually rated for 4 psi, but when they go out of stroke I think they have a tendency to spike the pressure and push fuel past the needle and seat. Plus the flow is too irregular to work very well consistently . Maybe someone else’s has made one work, but I have never had success running them with carb with the mechanical pump, or by themselves either for that matter. I thought maybe it would halfway work in series with a mechanical pump, but that wasn’t the case. The pusher pump needs to be a vain style pump like the Holley red street pump or Carter Street pumps, or similar pumps to work very well. Something that has a built in regulator with consistent pressure, and doesn’t just go out of stroke when there is no demand.


I have two cars with in tank pump Tanks Inc systems feeding carbs. They work pretty much flawlessly, but are quite a bit more elaborate to set up versus the pusher and mech pump with the check valves. On my cars with Tanks set ups the fuel system was done from scratch. I just tied into the stock line adding the pusher pump with the stock mechanical pump on the pusher pumps.

Versus feeding a fuel injection set up, the in-tank set up returns a lot more fuel when set for the low pressure. The return line really needs to be as big as the feed line. My cars with the in Tanks setup are hard to keep clean where the tank vents from the fuel vapors. I suppose you could use a charcoal canister and fix that. Lots of vapors coming out of it on a hot day though, might take a couple canisters and a pretty elaborate set up to the carb for making it happy. The vent is stupid simple.

I have another car with a sump welded to the stock tank and is all electric with tandem electrics. One pump pulls from the stock factory pickup, and the other pulls from the sump with a check valve inline, running low pressure street pumps with no regulator, ussually kick in the sump pump at the track. I have another car with a fuel cell and 2 holley's blue 15psi pumps and a fuel regulator. 2 trash grinders is a bit on the loud side!

That's how I set them up here. Yeah it's a bit involved to set up and when said and done costs about a grand start to finish but it's a fantastic setup for a bigger HP carb setup, and about a necessity if going EFI.
In fact I ran these Tanks Inc fuel setups on carbs for years and when those cars were switched to EFI, it was just as simple as changing the spring in the regulator for EFI pressures and done.
When I do this I always set them up with 1/2" feed and return lines so when I'm running carb pressures, the 1/2" return does the job.

If the car is equipped with the charcoal cannister, I use it. This requires welding some extra connections on the Tank Inc tank so I can hook up all the lines required, but will function as the factory intended when finished, and vent through the cannister. Works excellent.

In fact the Tanks Inc systems have worked so well for me I completely modified the floor of a Vega I'm restoring now just to accept a 2nd Gen F-body Tanks Inc 21 gallon tank, complete with a walbro pump and sender etc.... It's also getting 1/2" feed and return lines, and will be supplying fuel to a carbed 500hp 327. That way the fuel system is solid and ready for more power later.

Been running the SD TA that H-O Racing built for street the way they set it up for a Q-jet for 44 years.

They used Carter pumps on it. Rotary mounted in front of the tank to a larger than stock line to a mechanical Carter on the engine. The original Rotary electric finally failed about 8 years back so just replaced it with another identical unit from Carter. Still has the mechanical pump that was on it in 1979...
My understanding was that with the small fuel bowl of the Q jets having more volume (not pressure and IIRC it is the lower 4ish psi unit) is key and helps at the top end keeping the bowl full.

I don't believe it wears out anything having both a mechanical and electric rotary.

Just under a grand is pretty close to what I spent not counting labor, 1/2” the entire way.

Good good to know that the existing charcoal setup can work with the tanks system. So far I have put them on 69 and older cars without a factory charcoal canister. I would want to try running if the system was on the car already.

I've been really closely pondering something like this. But I've had some thoughts that are maybe specific to just how I think about things...

• I am sorta into really minimising the modifications (especially obvious ones). For example, I sorta really want to keep the stock pump-to-carb hard line and mechanical pump
• I'm pretty keen that an electric pump not stay running in case of an accident or something. Usually this means an oil pressure switch in conjunction with something that can override that while starting
• I hate electrical complexity
• I hate the sound of an external electric pump
• I don't want to have to replace the tank and replumb everything

So what I've been leaning towards as an idea is this:
• Keep my factory style mechanical pump
• Add a pusher pump with bypass like https://www.summitracing.com/parts/crt-p4602rv
• Add a full throttle switch like one of these "nitrous switches" and tie that to the electric pump

To my thinking this could be about perfect. Nice quiet stock functionality for most street driving. Electric kicks in for passing and at the track without me having to remember anything. I can just briefly hold the pedal down for a few seconds before starting if I want to prime. No worries about the pump running when the motor's off because of the throttle return spring and no need to plumb some oil pressure switch.

To my thinking this seems almost a flawless plan. Am I missing something obvious? Has anyone used a good WOT switch that fits nicely to a QuadraJet?

Sam

Have you considered using an automatic 'Downshift' switch?

Thank you all.
 

Thanks for the response. 👍

I would want a roll over safety switch even in a street car that has a electric pump that I have added!

glhs: that's the way to go. Like 455dan says: "been running that set up for 44 years"

I had mine (Holley Red Pusher Pump/Carter Mechanical) wired that way for a while. After I had my very first vapor lock symptoms occur, I switched to a toggle under the dashboard. Pressurizing the system eliminates any tendency to vapor lock in hot weather.

I never have found the need to run a bypass. While I was installing, I checked it with a hand vacuum pump and a vacuum gauge and found the same vacuum drawing through the pump as through a plain 3/8 hose. The Holley pump did not impede the draw of the mechanical pump and I mounted it below the level of the fuel outlet on the tank.

I run a dual feel Holley and have never had a fuel starvation issue but can't speak for those who run Quadrajets with their smaller bowl capacity.

I can tell you a mechanical can not pull through a Mallory pump! The Carter I had on the old 409 Impala in high school yep just on when racing otherwise the mechanical fed the dual quads.

Yeah, the way the Holley is constructer, the vane rotor is an eccentric and only has close contact to housing at single point. The inlet and outlet are positioned so as to allow free flow around the rotor. It's not a particularly efficient pump but only needs to deliver 5.5 psi when running.

You can hold it up to your mouth and blow air straight through it when turned off.

I keep things looking stock, including "dummy" mechanical pumps.

It's pretty easy to fab up stuff to look like it works and still have a good fuel supply system with an in tank electric pump.

I've even done that on EFI systems so the car still looks like it's using a carb and mechanical pump. So worrying about things not looking original really isn't a concern with a little ingenuity.

You know, it's one of those products I'm surprised no one has made. If I ever went to an in-tank pump I'd want a fuel pressure regulator in a mechanical pump housing. I'd bolt it to the side of the block just like a mechanical and no one would think twice about the return line from it. I'd love that!

Sam

If you choose a mechanical pump that has a return port like the Carter M6907, you don't have to worry about over-pressurizing and rupturing the pump's diaphragm.

A few thoughts on combinations.

Impossible to pull fuel through a gerotor style pump.

Hard, but somewhat possible to pull through a vane style pump, but the fuel will be spinning the vanes to get through the pump.

Fairly easy to draw fuel through a pulsating pump since it is basically free flowing through check valves. Unfortunately any restriction back at the electric pump is going to create more of a negative pressure and the system is going to be much more prone to vapor lock with the pump off. Besides the negative pressure the physical restrictions of the pump or bypass check valves is going to limit flow and possibly lead to starvation at heavy throttle. Wheelspin (Les) and I did quite a bit of testing on his GTO and the TA and despite our valiant efforts found that the electric pump needed to be running even taking a brisk run up a long freeway onramp. Even though the front pump was a RobbMc 1100HP he was experiencing the dreaded drop out at the top of 2nd gear. Adding the electric pump back near the tank totally solved the problem when the pump was on, but even with the bypass check valves the fuel starvation happen sooner if the pump wasn't on. So he ended up running the pump most of the time. Hindsight says that we should also have added an additional circuit that would turn the pump on with anything over half throttle position.

Also found out contrary to what was said on the internet that adding a 6 PSI electric pump to a 6 PSI mechanical pump didn't keep the output to the carb at 6 pounds. With the electric pump running we were seeing almost 9 PSI so we had to add a regulator before the carb.

It really makes no sense to put a mechanical pump in front of a good electric pump as it simply becomes a restriction for it. Electric pumps are "free flow" and mechanical pumps have valves that open/close and obstruct the flow from the electric pump.

I'd add that unless you are using a rear sump, in tank pump or fuel cell running an electric pump in front of the tank will still have limitations as you need to do two things when using an electric pump It needs unrestricted feed and works better if placed BEHIND the tank vs in front of it, at least if you have a pretty fast car. This allow us to use the forward movement of the car to help feed the pump, vs trying to use it when the car leaves hard and all the fuel is pinned up on the bumper!..

I've tried every conceivable combination of tanks, sumps, fuel cells, line sizes and electric/mechanical pumps over the years. For the most part you can get away with a small electric pump in front of the tank feeded an engine mounted mechanical pump with mild to moderate performance improvments. Even so, when you really start hooking up and leaving hard the factory in tank pick-up becomes the stumbling block no how many or the location of the pumps in front of the tank.......FWIW......

Agree, which is why the Baffled "Tanks, inc" fuel tank does a better job with a EFI pump located in the front of the tank vs a pick-up in a fabricated sump and rear mounted
electric fuel pump.

Also the tube fuel level sender works a Lot better vs the "Toilet Bowl Float? factory type
sender.

The factory stuff with a rear sump WILL get you some capability with modifications to the tank.

Tom V.

I could not agree more with what Cliff and others are saying !
Look at it from the logical point of view that there are companies that make both electric and mechanical fuel pumps, yet they do not offer both in conjunction / in a kit so to speak with each other.

I rest my case that I started back in post #2 of this string.

For a street driven car if you loose your electric you are calling AAA or walking.Happened to me and the factory pump went on the car the next day and never looked back.FWIW,Tom

And this is the STREET section.Tom

Why cant you folks just admit the fact that if you have a electric pump that’s not on you then have some level of a restriction taking place, it’s just that some folks cars are making enough HP and accelerating hard enough to experience that fault.

In fact if you want to get right down to it and detailed about it every added bend / angle in the system joss or fitting wise as when using a bypass check valve at the pump is a restriction.

With the pump in the tank the chances of it dying are very slim. It's basically the same setup that every OEM has been using since the 80's which has proven to be very reliable. Typically a proper setup like this will go 100k miles and/or 10 years or more without a hiccup.

As a precaution, I set them up here with a trap door in the trunk anyway. So in the event I ever have to change the pump I can literally have it out in 10 minutes without even dropping the tank, or even worry about draining the tank. So if I wanted to take a 2000 mile road trip across country, the smart thing to do would be to just carry a spare pump just in case since it's a simple 20 minute road side repair with a trap door. No different than what I would do with a mechanical pump car, I'd carry a spare mechanical for those long trips.

Changing the mechanical pump actually isn't as fun though, laying on your back and getting gas in your armpits on the side of the road. The trap door in the trunk to swap the in tank electric is actually an easier swap.

It's pretty easy these days to exceed the stock mechanical pumps ability to keep up with a street car. You can pretty much throw an engine together today with off the shelf parts and not think too hard about it and make 500hp. 600hp isn't much more difficult either. A mechanical pump just isn't going to cut it with setups like that.

You might be able to putt around town but any rambunctious driving is just going to show itself. Especially if the car hooks at all.

I just wanted a priming system for tri-power to be used after long inactive times with all gas evaporated from carbs. Hard on starters with extended cranking to fill carbs.

First used the electric pump and check valves and on a momentary contact toggle switch. Just hold the switch for 25-30 seconds then pump the accelerator once and it starts right up. But if I looked in the ends of the check valves it looked like a lot of restriction. So to get away from the restriction I changed to a switchover valve like would be used with saddle tanks on a truck. Same principle. Hold the momentary switch for a bit and start it up. If I was in a street race I could always hold the switch for a quick fuel boost. But I really don't drive it that way. Just a cruiser.

So in regards to the above comment you think that electric pump can push through a mechanical one if the motor is not at least cranking?

The electrical pump DOES push through the mechanical pump. Like Tom I've used a cheap $39 electric pump with a toggle switch under the dash to fill my float bowls if the car has sat for any length of time. When the float bowls are full and the little electric pump meets resistance it's tone changes so I turn it off. Then two or three pumps on the pedal and the engine starts right up. These are street cars not race cars so any restrictions have never been noticed by me. I did this because I didn't like grinding the starter to get the mechanical pump to fill the float bowls.

Steve,like John said.On my Lemans I just turn on the electric and you can listen to the pump when the flote bowls are full it changes tone.Pushes thru my Carter street pump with no problem.Tom

Humor my rambling...

Seems there are two scenarios being discussed: 1. priming a carb and 2. supplementing a mechanical pump. To me, priming is of interest but needs little flow so is easier. Goal 2., which OP seems to want, sounds difficult.

As to priming through a mechanical pump, I think they just have simple flapper-type valves on inlet and outlet so should be easy to get some flow if electric pump generates the same low pressure. The check valves in the pump operate just fine with the low pressure the mechanical pump diaphragm generates so should also work with an upstream low-pressure electric.

For priming only, my guess is the impulse pumps will be less likely to overpressure the mechanical diaphragm and offer less restriction to the mechanical pump than a rotary-vane pump.

Pushing high volume through a mechanical pump sounds difficult, if not impossible, without overpressuring the diaphragm in the mechanical. Those check valves are probably what limits the flow. Pushing harder on them will certainly flow more but the higher pressure needed would add risk and complexity.

I like the idea of an empty mechanical pump body with an electric pump doing the real work.

I used an AC Delco EP12S inline electric pump. Quiet and reliable. Small and easy to mount. They don't lift fuel very well, so mounting it low on the frame is a good idea. Mechanical pump has no problem pulling fuel through it. I like the overall safety and reliability of a mechanical fuel pump. But for priming an engine that sits for long periods or has multiple float bowls, priming with a small electric pump makes starting much easier. Electric pump also helps in hot weather vapor lock situations by keeping the fuel line under a little pressure raising the boiling point.

I've posted this on here in the past because this topic has come up several times over the years, but here is the pusher (priming) pump setup in my '63 Catalina. The pump is grounded on the frame and the wire going up into the floor goes to the toggle switch under the dash.

Sounds like many have done this & the electric pumps do indeed push through the mechanical pump when not cranking or when running... & vice versa that a mechanical will pull through the right type of electric pump.

Ive read about this for years on here and seems to work fine for those that do it, for starting after sitting awhile as well as for added fuel supply when needed.... its not ideal for added fuel supply but it works when set up right.

Bypass circuit
 

Went with a Carter 4603 electric fuel pump and a By-Pass Circuit some years later.
Very dependable. E-pump was off unless priming carbs or "acceleration runs on the street". Fuel went thru the by-pass to the mechanical fuel pump.

Tom V.

Tom

Would you send a diagram of the by pass circuit? Thanks

Tim, here you go.

Picture is worth 1000 words

Tom V.

OK, help me here.

Is the benefit of this bypass config just to avoid a flow restriction when running only the mechanical pump?

If, OTOH, the electric pump is used to add more flow at the carb, it can only do this by adding more pressure, right? So does this mean you MUST also have a regulator to stay carb-friendly?

I measured the inlet pressure that overwhelmed my needle and seat, and it was 12 psi sitting still. I guess if a mechanical pump typically delivers 5-7 psi, there is some margin to allow maybe 4 or 5 psi "boost" from the electrical pump. If flow through the mechanical pump is directly proportional to pressure, then the electric pump could almost double the flow ?? So does that electric pump have a low-pressure output or do you need a regulator somewhere to stay carb-friendly?

Mike

I’m curious about this as well, ever since I heard about fuel evaporating from the bowl.

I’m thinking of the primer need, not a booster when getting on it, and something that works like modern FI cars. To that point, is there a “momentary” relay, or similar animal? A gizmo that is triggered when ignition is in the run position, but will only stay on (closed) for a short period of time?

I searched the web, but I’m not too bright when it comes to detailed electrical jargon. Does this site cover something that fits?

https://www.macromatic.com/support/k...elay-functions

I don’t think the “momentary” fuel switch will work very well. It takes to long for the pump to build pressure and purge the air out. It will get behind. Even my Walbro in tank carb set up takes a considerable amount of time time when it is first turned on to fill the carb. Longer anyway than a EFI set up, the lower pressure 7 psi doesn’t force they air out nearly as fast as 40 plus psi EFI set up.

Those diaphram pumps like the ACDelco and Mr Gasket are usually rated at 30 gph at operating pressure. I don’t know what the pressure and volume performance curves look like on those. My feeling is the mechanical pumps is doing most all the full throttle work if those pumps are feeding a mechanical pump. But I could be wrong, since I have never seen the performance chart. By itself 30 gph would only be good for 300 HP.

The Carter M6122 mechanical pump is rate for 40 GPH at pressure. Free flow is 120 gph.

The free flow of the Carter vane pumps is not published, but rated at 50 gph at pressure. My guess is it is about 100 gph free flow.

The Holley street pumps have higher ratings, but are rated differently than Carter. Not all that accurate in my opinion. The flow drops a lot with head pressure at the outlet, I think they run closer to 70 gph at a normal carb operating pressure. Just a guess though. Better than the Carter, not as good a 140 Mallory.

The idea of the pumps in series, both pumps do some of the work. The electric pump becomes a charge pump for the mechanical pump. Each pump has less losses. They operate at lower pressure on their performance curves. Not bullet proof for drag racing, but an improvement over a single pump that does not pull from a sump or a in-tank setup.

Jay,
the "momentary" switch is only a toggle switch that is spring loaded to return to its original position when pressure is removed from the switch. As long as you hold the switch it powers one circuit and when you release it it returns to its original position to power the other circuit. Completely independent of the ignition switch.