[KEN CROCIE]

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

[NeighborsComplaint]

Originally Posted by OG68

Have you considered using an automatic 'Downshift' switch?

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.

[Skip Fix]

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.

[NeighborsComplaint]

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.

[Formulajones]

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.

[glhs#116]

Originally Posted by Formulajones

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

[NeighborsComplaint]

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.

[lust4speed]

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.

[Cliff R]

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......

[Tom Vaught]

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.

[steve25]

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.

[tom s]

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

[tom s]

And this is the STREET section.Tom

[steve25]

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.

[Formulajones]

Originally Posted by tom s

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

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.

[Formulajones]

Originally Posted by tom s

And this is the STREET section.Tom

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.

[pfilean]

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.

[steve25]

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?

[61-63]

Originally Posted by steve25

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.

[tom s]

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