[pfilean]

Quote:
Originally Posted by pfilean View Post
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.

In my case I'm only trying to fill empty (3) carbs after extended down time. The engine is not running so ignition and throttle are not important. Momentary switch is independently powered. I could use the electric pump to try to help the mechanical pump, if necessary, which is seldom to never is.

The reason for the switchover valve is that I thought that the check valve trick might (stress might) add flow resistance through the check valve. Didn't want any unnecessary strain on the mechanical pump. Flow through the switchover is straight through with no interference.

[Jay S]

Originally Posted by Shiny

Thanks for the explanations. I apologize, but I'm still struggling to understand the pressure at the carb inlet when an electric pump is in series with a stock mechanical pump and there is low fuel demand.. (at idle).



This is the part I'm trying to understand. The term "regulate" is more like "self-limiting" I think. Because the pump is all diaphragms and springs, is the max pressure it can put out imited by the diaphram spring in this image:



But isn't the max (idle) output pressure of the mechanical pump always relative to the inlet pressure?

Similarly, doesn't an electric pump build pressure at its outlet when there is low flow at idle (or dead-headed)? It may be internally regulated or limited but I have to believe it is going to be 5-7 psi, correct?

So if the pressure above atmosphere (which is what a carb cares about) is 5 psi at both the outlet of the electric pump and the inlet of the mechanical pump, how can the pressure at the carb not be the sum of both "dead-head" or low-flow pumps?

I think I am missing something here about how the mechanical pump works because no-one on this thread has mentioned flooding at idle because the pressure got too high.

I think if someone measured idle inlet pressure at the carb with and without a series pump powered, I'd at least see whether the two pressures added or if the mechanical pump somehow delivers the same output pressure regardless of inlet pressure.

Mike

A mechanical pump fuel pressure is referenced to the atmosphere. Same as an electric. There is no reference back to the inlet pressure.

I have seen some old low boost turbo set ups where mechanical pumps ported a boost reference too the intake manifold. I think it is usually up on the side of body of the pump. Tom V probably has seen that also. I think I recall seeing that on Hugh Macinnes’s turbo charging book.

It is not usual to see the idle fuel pressure jump up a couple pounds with you turn the electric on though. But only a couple lbs, depends how the electric bypass is set, and how well the bypass on the mechanical pump works.

[Tom Vaught]

Some of the Chinese mechanical pump "knock-offs" have fuel pressures at idle at almost twice the old Pontiac fuel pressure numbers, (5-5.5 psi).
Chinese knock-offs closer to 8-9 psi at idle. Not sure where this 7 psi fuel pressure number comes from.

The Pontiac service manuals give the specs (if you have the right info) for a stock pontiac engine/carb fuel pressure.

Tom V.

[Keith Seymore]

Originally Posted by 78w72

What brand/model mechanical pump? Any bypass system like shown above or just pulling through the electric?

GTO: "stock" AC mechanical fuel pump

Chevelle: Holley mechanical pump

In both cases there is no bypass; stock system pulls through the electric pump when it is not on.

K

[Shiny]

Originally Posted by Jay S

A mechanical pump fuel pressure is referenced to the atmosphere. Same as an electric. There is no reference back to the inlet pressure.

I have seen some old low boost turbo set ups where mechanical pumps ported a boost reference too the intake manifold. I think it is usually up on the side of body of the pump. Tom V probably has seen that also. I think I recall seeing that on Hugh Macinnes’s turbo charging book.

It is not usual to see the idle fuel pressure jump up a couple pounds with you turn the electric on though. But only a couple lbs, depends how the electric bypass is set, and how well the bypass on the mechanical pump works.

Ahhhhh!!! Thanks for dealing with my confusion and answering.

I'll have to digest this, as I thought gas was pulled into the pump (or pushed in by an electric pump), the diaphragm started moving, pressure built up, the inlet valve closed, and gas exited through the check valve at the outlet.. so I've got to figure out why if the gas was above atmospheric going into the pump chamber, it wouldn't stay at that pressure.

I understand if the mechanical pump was "off" (pretend the lever wasn't being actuated), an electrical pump could push right through it. If it didn't work this way, an electrical pump couldn't prime a carb.

So you are probably correct about "relative to atmospheric, not inlet pressure", but how that works remains unclear to me.

I still somehow think if you plugged the outlet of the mechanical pump, you'd see the pressure generated by the upstream electrical pump inside the mechanical pump chamber, whether the mechanical pump was operating or not. And this pressure would be above atmospheric, any pressure generated by the mechanical pump would raise it even further. This is where I'm still stuck!!

I probably has to do with the way the mechanical pump pressure is limited but I'm not clear on all this yet....

hmmmmmm...

Mike

[Dragncar]

I got down to 12 flat with a 80 gph Holley mechanical pump with 3/8 line with sock off and a piece of hose extending it.
Went to a Holley Blue pump dead heading it it. No real difference.
Once I put a roller cam in I ran 1/2" line with Mallory return regulator. I soldered a 1/2" steel line from the front of the tank to the bottom point. Pump is in the front of the tank and the bottom of the pump is about level with the top of the tank. Never had a issue picking up fuel. Car was running mid 11s. 60 foots in the mid 1.5s.
Then I bought a 140gph Holley knockoff pump and the car car got down in the 11.30s. Other changes were made so all of the improvements were by no means all fuel related.
Then I got a hair brained idea and thought I would try it.
Always wondered if the 140 was big enough to keep up and the 3/8" line was still there. Tank had a 1./2" line and a 3/8 line picking up fuel from just about the same location in the stock tank.
So I put my old Holley 80 gph mechanical pump back on the 3/8" line and rant it to the primaries . That pump does not require a regulator.
I have a return regulator on the 1/2" line on the other side of the car and that goes to the secondaries . So the 140 pump just by passes back to the tank unless the throttle is mashed.
Well, it worked just fine. Never had a issue with it in any way. People thought I was nuts.
That is the fuel system that was on it when the car ran its best.
10.82 @ 121 mph with 1.43 60 foot.
I will give the system another shot only with a new 110 gph pump on the primaries just for time sake.
Everything is not going my way this summer, cam issues, work issues and now a heart by pass in the family we have get through.
When we get back from that I will thrash to get the car out for the last month of the season.
I have a 5 gallon fuel cell I can put in and bought one of Langers old pumps if I have any issues delivering gas.

[GTO TEX]

Originally Posted by 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.

The GTO currently will make full 1/4 mile pulls @ 11.58/7.37 1/8 mile with only the mechanical RobbMc 550 pump with 3/8" supply line @ 7 psi. When I got the car I had an issue with low pressure at WOT (3 psi). Sent the pump to RobbMc and found the restrictive fitting on the fuel vapor line went missing not allowing the pump to build pressure. This corrected the fuel starvation issue although the car will mph 1.5 faster in the quarter with running the electric pump. I am planning on swapping to the RobbMc 1/2" sender with -8 to the pump with a replacement Carter electric in anticipation of some possible engine changes.

[Cliff R]

Just a few side notes here to add to my first post.

This is a topic where some folks run very well w/o apparent issues with pretty basic set-ups and others can't get out of the 13's trying to do the same thing.

My opinion here is to install a system that is EASILY good for a LOT faster than your car should run at the track.

Also keep in mind these two things. I raced my car for years with nothing more than a larger 1/2" feed line in the tank, a Comp 140gph put right in front of the tank, then fed a Carter 120gph mechanical pump, then on to the carb with 1/2" lines everyplace. I also bypassed the mechanical pump with no change at all.

The car never nosed over once, but only ran around 108-109mph and typically 12.40-12.60's. It did "feel" a little "soft" up near the shift point of 5500rpm but I just figured it was running out of camshaft and head flow (RAIV cam and 6X-4 heads at 232cfm.

Over one Winter I yanked ALL of that out and sumped the tank, moved the 140gph electric pump behind the tank, Holley regulator right in front of the carb, and 8an lines fittings everywhere.

To my surprise on the very first outing I ran 12.0's at 112mph (in the heat) and the engine spun so quickly past 5500rpms I couldn't move the shifter fast enough!

So the entire time I was "marginal" for fuel delivery for the power level and vehicle performance but never knew it. I went on to make other changes and run a LOT quicker, and never experienced a hint of any fuel delivery issues since even with much more powerful engines installed and running a lot quicker at the track.....FWIW....

[jhein]

I've thought about an electric pusher pump before so this is an interesting discussion.

I had some really bad fuel starvation initially with the new motor. The first problem was improperly vented tank, which most people probably won't have, but it's something to think about. That made a huge difference in my case. But my 120 gph Carter style pump from BOP still wouldn't keep up. The RobbMc 550 pump stopped any overt starvation but as Cliff said, I think more fuel would still improve things. My next step will be a 1/2 or 8AN line and pick up and a baffled tank.

I know the ultimate setup is the in-tank electric and if I was racing and wanted every tenth, then that's the way to go. But for a strictly street car that's not what I want.

[Cliff R]

One thing that I am NOT fond of with any of this is having to run more than a stone stock fuel system when we start upping power levels and take other steps (DOT's, slicks, suspension mods, etc) to make our car leave harder and quicker ET's on race day.

Like many others I prefer the stock look, simplicity and reliability in long term service of the stock set-ups. I am NOT fond of any type of electric pump and not overly fond of the high output high pressure mechanical pumps. It would certainly be nice to be able to run "stock" parts and still bust right into the 11's or even quicker without putting in a fuel system that delivers a "garden hose" of fuel delivery no matter how hard the car leaves.

Sady enough that's just NOT going to happen with most of these cars, big HP/Torque upgrades, etc, and rest assured you can NOT defy the laws of physics with these things. When you are pinned HARD against the seat in a WOT run ALL the fuel in the tank is pinned up on the bumper!!........

[Tom Vaught]

Originally Posted by Cliff R

Sady enough that's just NOT going to happen with most of these cars, big HP/Torque upgrades, etc, and rest assured you can NOT defy the laws of physics with these things. When you are pinned HARD against the seat in a WOT run ALL the fuel in the tank is pinned up on the bumper!!........

INFO FOR MY 64 GTO EFI / CARB FUEL TANK WITH INTERNAL BAFFLES:

https://www.tanksinc.com/index.cfm/p...rod/prd417.htm

1964 Pontiac GTO, Lemans and Tempest EFI Gas Tank
Fuel Injection Ready!
Includes 2 piece neck design that connects with supplied 2" ID rubber hose
Utilizes our GPA series fuel pumps, available in sizes from 109 to 450 liters per hour.
Uses aftermarket 5-bolt senders. Multiple Ohm ranges available to work with factory or aftermarket gauges. If using tube sender length is 6"
EFI style internal baffling with extra large 4.8 liter dual tube baffled fuel tray to prevent fuel pump starvation.

Perfect for your Pro-Touring, Autocross or Road Racing Ride
Fuel pump and sender are recessed in the tank for easy installation with no modification needed to your car.
Looks like an OE tank when installed.
Coated galvanized steel then Powder Coated Silver.
24 Gallon Capacity
1" Deeper than stock


SO THE FUEL CANNOT RUN AWAY FROM THE TANKS,inc PICK-UPS ON A DRAG RACE LAUNCH. BUT it will "run away" on any factory GTO tank.

Tom V.

[Tim Corcoran]

Originally Posted by Tom Vaught

Tim, here you go.

Picture is worth 1000 words

Tom V.

Thanks Tom

[Cliff R]

That's some cool stuff right there Tom. If I had to do it all over again with the Ventura I would have replaced the tank with one set-up with baffles and a pump in the bottom of it instead of welding the CE sump on the stock tank. I never liked the look of the sump nor having to mount an external pump behind the tank tucked up in front of the bumper. With these things it is ALWAYS better to push ALL the fuel vs running any sort of suction line from the tank to the pump, especially if the electric pump is mounted in front of the tank.......

[Formulajones]

In your defense Cliff, and actually many of us that have been around this hobby long enough, that was your only option decades ago. We had to sump stock tanks and run big external electric pumps just to feed these engines if you actually had something that ran decent back then.

The only other option was a custom made tank and pump setup that was extremely expensive at the time, almost no one was doing that on their hot street cars.

It wasn't until Tanks Inc came along in the late 80's or early 90's when things started to look better as far as affordable tanks with electric pumps in them for us classic car guys. And even then they only started with street rod stuff, it took many years as more models became available for different types of vehicles. They've been expanding ever since. So we had to wait a long time from the days when we ran those external pumps and sumped stock tanks to have something that literally just dropped in the stock location and looked factory, but with modern fuel system performance.

Now it's just a no brainer to get an EFI style tank from Tanks Inc, even if you run a carb, and just put the pump in the tank, run lines big enough, and call it done. It's clean, it's simple, and it works.

No longer is it necessary to sump stock tanks and run big external pumps that sound like weed eaters, and of course can't forget that giant fram filters hanging down LOL, that is unless you're just going for that day 2 old school appearance and have to have all that stuff hanging below your back bumper

[Formulas]

To anyone interested in momentary powering of a electric pump

you can use the factory provided TH400 kickdown switch to trigger a relay for pump power

so imagine anytime you stomp the go pedal you have extra fuel flow

and for extended storage get in turn key on depress the gas pedal and your priming

pretty easy to do..

i favor two seperate fuel feeds and a check valve vrs two pumps in series so your not trying to pull fuel through a inop pump and two tank outlets are even better so you have two entirely seperate systems

with two seperate pickups at the tank you could feed the front of a Holley with the mechanical pump and feed secondary side with a momentary electric pump without a check valve

[David Jones]

I've run a Carter P4070 electric pump mounted between the tank and the rear axle and a factory mechanical pump on mine for 15+- years. I have the electric switched and generally keep it off...unless I'm really going to hammer on it for a while.

[Dragncar]

Originally Posted by Formulas

To anyone interested in momentary powering of a electric pump

you can use the factory provided TH400 kickdown switch to trigger a relay for pump power

so imagine anytime you stomp the go pedal you have extra fuel flow

and for extended storage get in turn key on depress the gas pedal and your priming

pretty easy to do..

i favor two seperate fuel feeds and a check valve vrs two pumps in series so your not trying to pull fuel through a inop pump and two tank outlets are even better so you have two entirely seperate systems

with two seperate pickups at the tank you could feed the front of a Holley with the mechanical pump and feed secondary side with a momentary electric pump without a check valve

Two separate pickups with a mechanical feeding the primaries does work. I did not use a check valve with my system. But a bypass regulator for the secondaries.
80 GPH to the front with 140 gph to the rear.
Next one with have 120gph to the front and 140 to the rear. 260 gph total is a lot of fuel.
They should keep up or a BG 400 is going on.
I know a guy who ran real fast with 2 Holley blue pumps. One to each fuel bowl.

[Tom Vaught]

So did I, my guy's name was Grumpy Jenkins. Not a Pontiac guy though.
At the time the Blue pumps were about the ONLY choice for the Higher HP engines.

Tom V.

[Tim Corcoran]

What I got from this thread is the most important thing is picking up fuel from the tank. The factory tank and pick up works fine for what it was designed to do but under hard acceleration the fuel climbs the rear of the tank and uncovers the inlet tube. Three choices, sump the factory tank (requires a good welder), install an aftermarket fuel tank and in tank pump or install a fuel cell.

Is there a way to modify the pickup tube to move it to the back of the tank?

[Gach]

Originally Posted by Tim Corcoran

What I got from this thread is the most important thing is picking up fuel from the tank. The factory tank and pick up works fine for what it was designed to do but under hard acceleration the fuel climbs the rear of the tank and uncovers the inlet tube. Three choices, sump the factory tank (requires a good welder), install an aftermarket fuel tank and in tank pump or install a fuel cell.

Is there a way to modify the pickup tube to move it to the back of the tank?

Exactly, on the street usually the mechanical pump works ok cruising around. Unless like your pointing out, the fuel moves away from pick up. Especially if tank is say 1/4 filled. But racing even if on the street with just a mechanical pump Eventually end up with issues. I can remember chasing those issues. Finally to resolve those issues end up sumping tank, and running a Holley blue pump, Eventually as hp grow, ended up having to go with 2 Holly Blue pumps.