CDaniel525

I am thinking of getting a Holley Black "pro-Series" electric fuel pump to accomodate future nitrous, but i was wondering if i can use my mechanical pump in conjunction with the electric??
What would be the best way to run the fuel lines??
I was thinking.....gas tank to the elec. pump, to the engine bay, split the lines with one going to the regulator, and the other to the mechanical pump, and then back into the elec pump line before the regulator or right into the line going in the carb??


Or is this just a rediculous idea that shouldnt be done??? LoL :crazy:
Thanks
Chris


[Modified by 74VETTE, 8:43 PM 11/12/2001]

daily_driver

electric pumps have been in use for a long long long long lonnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnng time

i doubt youd need a backup!!!

Barry's70LT1

Hi Chris...

Back in the "old days" when I did some racing, I installed an electric pump
at the tank, and kept the mechanical pump as well.
I had to block the return line as the electric pump was a diaphram type that
would pump until reaching pressure then it only pumped when the pressure
dropped.

I didn't see any performance improvments.

Eventually I had to remove the electric pump due to frequent vapor locks.
With the return line blocked, the fuel temperature would get too high causing
percolation.

Without the electric pump, I still managed 13.02 @ 110

Just my experience.
Thanks
Barry

CDaniel525

Thanks guys...just taking as many precautions as possible with NOS since i am going to install it sooner or later.
Chris

Tom454

I am interested in this topic as well... using an electric (non-tank mounted) fuel pump as a backup for a mechanical pump. My interest is purely for long trip security though. Anyone out there done this? What are the issues? E.G.- if the electric pump was in series with the mechanical pump, and the mechanical pump diaphragm was leaking, the electric pump would pump fuel into the oil pan... eh? How about one way check valves? Dual plumbing up to the carb line? Come on you mechanical engineers.... how could this be done? Show off your wizardry!

lars

On all the race & performance application cars I've been building, I've been installing an electric fuel pump back at the tank in addition to the mechanical pump on the engine. This has eliminated the second gear lean-out tendency of a mechanical pump used in a drag race application, and has eliminated hot-weather, high-altitude vapor lock on customer cars. A few notes on this:

I have found that electric pumps will have very short lifespan if the fuel is dead-headed. This overheats many pumps, and increases amp draw significantly. To counter this, I always run a fuel return line back to the tank when using an electric pump along with the mechanical. I run the return line as close to the carb as possible, thus always keeping cool fuel circulating all the way up to the carb. I run a small restrictor oriface at the return line to keep fuel pressure up while allowing fuel circulation. This works very well, and eliminates the lean-out condition as well as vapor lock problems.

With an electric pump, safety is of major concern. Normally, the electric pump is wired into the ignition side of the electrical system. Thus, an electric pump will run whenever the ignition is in the "on" position. If you're ever invloved in an accident and become incapacitated, the engine may be dead, but the electric pump will continue to pump fuel. You can imagine how dangerous this could be. Crispy critter.

For this reason, I always wire the electric pump through an oil pressure switch. Holley makes an oil pressure switch that will allow current flow to the pump as long as the engine has oil pressure. The pump will be shut off once oil pressure is lost (engine dies) even if the ignition is still "on." You also wire the pump into the starter solenoid wiring so that the pump runs whenever the starter is being cranked (no oil pressure at start-up, but pump runs when the starter is engaged). This keeps the installation safe and practical.

You don't need a very big electric pump to compliment the mechanical pump - just something to pressurize the fuel line from the tank to the mechanical pump. And make sure you install it with some rubber mounts so you don't get all the pump noise into the car.

CDaniel525

Sounds like a good install lars, as well as safe! Do you think it is suffucient enough for nitrous though??
Also, what is an oriface, and where to get one?
One other thing is, with the electric pump, can i use the original fuel lines to the engine compartment, or should i run new rubber hoses to the front??
Thanks again
Chris

RatRacer

There is another way of handling this issue. I used a Ford inertia switch from a Mustang that acts as a electrical breaker that cuts power to the electric pump in the event of a colision. I mounted it on the rear frame rail near my electric Holley fuel pump. I got it from a parted out Mustang for $5.

lars

Most mechanical pumps by themselves have enough capacity to handle any engine/power requirements. The problem arises with the pump at the engine "sucking" the fuel from the tank, up the line and to the pump with the added resistance of the g-force during acceleration trying to push the fuel back to the tank. This creates a low pressure area in the fuel line near the pump. In most cases this is not a problem. However, many areas of the country have gone to oxygenated fuels where MTBE or Ethanol is used as an additive in the fuel. Problem is, these additives have a higher vapor pressure (they boil at a higher pressure) than straight gasoline, and depending on how much of the additive is used and the exact formula, the suction created on the fuel line can create vapors at the pump inlet - classic vapor lock under high-flow, high suction conditions. The instant the pump gets a gulp of vapor on the inlet side, fuel outlet pressure drops to zero and the car will fall on its face no matter how good the pump is, and no matter how perfect the fuel line and feed system is. I've seen it happen repeatedly up here at our 6000' altitude where we're forced to use these oxygenated fuels. A small boost pump at the tank to keep the fuel line under pressure solves this problem.

The boost pump should not be used as a Band-Aid to mask other system problems. It is imperative that all aspects of the fuel supply system be in good condition, with no kinked hoses, blocked vents, or plugged filters. But depending on the fuel you're running and other conditions, a boost pump may be needed to eliminate the fuel starvation problems caused by high fuel vapor pressure.

Once you have eliminated the fuel starvation problem caused by the higher vapor pressure of the fuel by simpy adding a little pressure to the fuel line, the mechanical pump will deliver large volumes of fuel at good pressure - adequate for most nitrous systems. It doesn't take much of a boost to accomplish this.

The stock fuel lines are plenty adequate for most applications. I would stay with the steel lines as much as possible, running rubber hose only at the connection points. The less rubber the better when you're running pressurized systems. But install all new rubber hoses at these points to assure no kinked hoses and to assure that the hoses are in good, leak-free condition.

gearheadz

So Lars...in your example, the return line is fed off of a "T" connection in the fuel inlet line between the mechanical pump and the carb (closer to the carb = cooler fuel).

I've seen some return lines connected AFTER the secondary bowl inlet of a dual feed carb (i.e. Holley dbl pumper, Demon).

Fuel Circuit: Tank>Inlet>Mech.Pump>Pri.Feed>Sec.Feed>R eturn>Tank

Have you seen this? Advantages...disadvantages?

Also am I correct in understanding that the need for a return line is to prevent the electric pump from burning itself up by its continual pushing against the backup of fuel (at the mech.pump)?

Mark


[Modified by mdsmith, 9:31 PM 11/13/2001]

Tom454

I'm not sure if the original question (mdsmith) has been answered or not. Please bear with me here- There are (I think) two different objectives being discussed here-
1) An electric pump as a "backup" (just to get home)
2) An electric pump as a "supplement" (racing & nitrous & altitude & oxygenated fuel etc)

I'm also not sure if the plumbing for each would be the same. Maybe they can both be satisfied with one accommodating design.

I would define "backup" as an arrangement where the electric pump is not being used until the diaphragm in the mechanical pump fails... then, a switch is thrown to activate the electric "backup" pump to get the car home. This would be a benefit if my wife is driving the car and the mechanical pump fails. Aside from her own safety issues, if she left the car, it may not be there when I get back to it. If you've ever driven on the Cross Bronx Expressway in New York, you know what I am referring to. In this case, you are not relying on the electric pump to be "on" in order for the engine to function. So, it would be "off" until necessary.

I would define "supplement" as an arrangement where the electric pump is on all of the time along with the mechanical fuel pump to address issues such as posted above by a few members. This would mean the electric pump would be on continuously, not just being used as a backup.

In either case, the wiring issues would be the same, except that the "backup" scenario would require a manual on/off switch for the electric pump. If you really want to be thorough, you could also add an "inertia switch" which is common in contemporary fuel injected vehicles (edit- as cam potter already mentioned and I failed to notice). This switch shuts off power to the electric pump in the event of a collision and must be manually reset. Both my Crown Vic and my Mustang have this switch. The question I had/have, and maybe mdsmith still has, is "How do you plumb the system?"

If the diaphragm in the mechanical pump ruptures, and the input line leading up to it is pressurized by an electric pump, is there not a possibility that fuel will be forced past the diaphragm and into the cavity where the pump rod resides, and then through the oil drainback hole into the oil pan? And.... how about the same thing happening due to back pressure from the carb? How about fuel finding its way to the weep hole in the mechanical pump under the same conditions? I have seen pumps leak at the weep hole when they fail. Anybody have a plumbing schematic that addresses these issues? Are one-way check valves inserted into the lines?

RE: Rubber fuel lines- I use rubber lines all of the time because I maintain my vehicles regularly, and I don't Bubba the connections. Even on my TriPower setup. But in this case, I think I (personally) would stick to steel wherever possible because some pressurized lines would be under the car and not easily inspected. You can buy those new-fangled spring/clip/o-ring fittings and tubes (for maintenance/removal purposes), then use an inverted flare tool to mate them to your standard steel tubing. If you have to use rubber, I would keep it to a minimum as recommended above.

So, again, anybody have a plumbing schematic that addresses the pressure/mechanical pump failure issues? Are one-way check valves inserted into the lines to avoid leaks at a ruptured mechanical pump? Or am I just being ****?



[Modified by Tom454, 9:12 AM 11/14/2001]

gearheadz

Lars Oh Lars.....please respond.

427V8

PLEASE don't use holly fuel pumps.
If they last an entire summer you'll be lucky.
I had to replace mine after about 6 months of use and I know of other people who have had them fail.
( of course the WAS a Holly Red pump.)

Mallory seems to make good pumps...

RatRacer

Funny, I've been running the same Holley blue pump for 5 years on my '71 LS-5. It's important to get full voltage to them. I run a heavy wire directly from the positive terminal of my battery to a bosch relay, then to the electric pump.

Cookwithvette

A friend of mine bought a 69 Camaro. This thing is incredible but caused him the most hair pulling trouble. Driven normally it would go 3 miles then knock like crazy and quit. Driven like the race car it is it would go 30 yards before acting up. Turns out that the guy he bought it from installed an electric fuel pump in the trunk rather stealthily. All the lines looked normal unless you got under the car and looked in one little crevice near the tank. The pump wasn't powered and got clogged with crap causing him to lean out. We figured that it was leaning out but had no idea why. That was so funny, months we spent agonizing over what the heck was wrong and it turned out to be a hidden fuel pump. It was there for NOS security too.

Tom454

Nobody engineered this stuff yet? C'mon... someone must have addressed the leaking diaphragm/back-pressure issues... please?

PRNDL

Tom, Limited tho it is, my understanding was that when an elec pump is piggybacked onto a mech pump, the purpose is to suplement the working mech pump, not to back it up if it fails - so the design of the dual pump system (if you can call it a "design") does not contemplate how it all works when the mech pump fails.

But it is still an interesting question: How do you design a system that will still work (ie, get your wife home) if the mech pump fails. MJ

lars

Tom -
If you're looking the create the "backup" system where the electric pump is used in the eventual failure of the mechanical pump (implying rupture of the diaphragm with subsequent fuel contamination of the engine oil), there is, indeed, a way to do this. There are solenoid operated valves and checkvalves available (from industrial valve and fitting supply warehouses and from industrial supply houses) that will route the fuel one way when de-energized, and another way when energized. We use these all the time in various test setups we do here at Lockheed Martin. If you hook one of these solenoid valves into the fuel system and wire it to the electric pump, the fuel would be routed to the mechanical pump in the "normal" mode, but when the electric pump was activated (in the event of mechanical pump failure), the solenoid would close fuel flow to the mechanical pump and bypass it. A checkvalve at the mechanical pump outlet would prevent fuel flow from reversing through the mechanical pump while the electric was running.

Building such a system would not be difficult, but it would be a little bit of work to do it right and hard-plumb it with the "T" fittings, parallel fuel lines, and the checkvalves and solenoid valve. I think it would be easier to just replace the mechanical pump once every 5 years as a matter of preventative maintenance since you'd be putting a lot of work and effort into preventing a seldom-occurring failure mode. You're probably more likely to blow an HEI ignition module and loose a voltage regulator than you are loosing a fuel pump without notice (most pump failures start off by some fuel "weeping" out of the weep holes in the pump).