Multiple Fuel Pumps (Injuneer please comment)

This came up on another thread. I have been trying to find out more about what happens when two pumps are connected in series. The standard way to explain this is to say that connecting pumps in series (the outlet of the first pump feeding the inlet of the second pump) doubles the pressure while connecting in parallel (both inlets drawing from a common source and outlets feeding one pipe) will double the flow.

The parallel situation seems pretty straight forward. But the series (e.g. an inline pump) is not. Is this what is meant: for two identical pumps connected in series, the combination will flow a given volume at twice the pressure as a single pump? An example: both pumps are rated at 70gph at 50psi. Connect them in parallel and you will flow 140gph at 50psi. Connect them in series and they will flow 70gph at 100psi? What will the series pumps flow at 50psi, double what one will flow at 25psi?

I think the above is correct. The practical impact is that if you want to increase fuel volume at stock pressure you can connect two pumps in parallel or replace with a single larger pump. If you want to increase pressure (to allow use of small injectors at higher pressure) add an in-inline pump.

Rich Krause

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'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"



[This message has been edited by rskrause (edited May 22, 2002).]

Personally I am not sure you would double your pressure. I think you would stay pretty much the same, because the first pump couldn't pump anything more than the second pump could take in.

What I am trying to say is, lets say you have the 1st pump rated at 255 liter/hour, and the second is rated at 190 liter/hour, I think all you could pump is 190 because of the restriction. So 2 of the same pumps could only pump what one is rated for.

Not sure if that is correct, but that is how I have thought of it.

If you have doubts, just run them in parallel, like the Turbo Buick guys do. They just mount 2 Walbro's in the tank.

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Rich, all of this is covered in Corky Bell's book on supercharging.

If I were you I would setup a 1 gal fuel cell with a secondary pump to provide the fuel needs (you are still using the Carrol SuperFueler/nitrous setup right?)

Have this teed into the fuel line to keep it filled. In effect you have a fuel cache. http://web.camaross.com/bb/smile.gif

-CAL

[This message has been edited by Luna (edited May 22, 2002).]

yea, series won't add fuel pressure persay.

I run a 2nd cell(nitrous) and it works great.

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Rich:

Yes, you are 100% correct, parallel doubles the "maximum possible" flow, series WILL double the "maximum possible" pressure.... in general terms. Not sure why two of the previous posts disagree that pressure can be doubled in this way. We do it all the time in design of systems for puming fluids in chemical and pharmaceutical plants....

I think what people are missing is that putting two pumps in the system will not automatically double the pressure in the system.... the flow-pressure operating point will reach a new equilibrium that is in fact a higher flow and a higher pressure.... depending on the configuration of the system into which the pumps are pumping. A recirculated, or even a dead-ended fuel injection fuel system incorporates a fuel pressure regulator to keep the pressure constant, so in no way will the pressure actually be doubled, but it could be if it was necessary, by cranking up the setting on the FPR.

And, you can put two pumps in parallel to gain more flow, and also gain more pressure at the same time. I know its confuing as he!!, and if you and I were at a table, I could explain it in about 2 minutes with a piece of paper and a couple of graphs.

In general, unless you want excessively high fuel system pressure with very sudden increases in pressure (e.g. - a dry nitrous system), I would go with two pumps in parallel. My two Bosch pumps are in parallel, and they operate comfortably at 58psi (4 bar). I run a dry nitrous system, but I don't need to alter the pressure, the MoTeC can simply adjust the pulse widths when it knows the nitrous is "on". I have one "master" switch that arms the nitrous solenoids, turns on the second pump, and tells the MoTeC that it is about to shift to the nitrous program..... it only actually does that when it knows the nitrous solenoids are open.

One day I was in the shop that does a lot of my work, and there was a Porsche in one bay... it had a 1973 VIN tag on it, but was mostly reinforced with tube frame, and had a fiberglass replica of a modern slant-nose body on it. The interior was two Momo seats, a lot of wire harnesses and a shift lever. It weighed absolutley nothing. Then I saw 4 Bosch fuel pumps in the nose compartment, hooked in parallel. I asked the mechanic why the Porsche had 4 pumps identical to mine, when I only needed 2 to support 800HP. He replied that the Porsche made twice as much HP as I did..... http://web.camaross.com/bb/biggrin.gif..... it had two huge turbos running at 29psi, with what looked like 5" ductwork on the discharge of each turbo.... The owner was looking for turbos that would give him more than 30psi.... I wonder how wild a ride that thing was???

[This message has been edited by Injuneer 94FormM6 (edited May 23, 2002).]

Fred: thanks. It is finally clear in my mind. In my own case of two non-identical pumps in series, the system works fine now that I removed the T-Rex, so I will go the parallel route only if future upgrades require it.

In case it's of use to anyone else, here's short version of what my problem was and how I solved it. My SC setup had enough fuel with a 255lph Bosch in-tank and a T-Rex in-line. Stock reguator and stock lines. It did need a Kenne Bell "Boost-a-Pump" though. When I added a small (150hp) wet nitrous shot on top the FP would drop when the nitrous activated. When I removed the T-Rex, problem solved. I assume that the T-rex was limiting flow in some way, since it has a lower flow than the Bosch ay max FP of ~55psi.

Rich Krause

<font face="Verdana, Arial" size="2">Originally posted by Injuneer 94FormM6:
Rich:

Yes, you are 100% correct, parallel doubles the "maximum possible" flow, series WILL double the "maximum possible" pressure.... in general terms. Not sure why two of the previous posts disagree that pressure can be doubled in this way. We do it all the time in design of systems for puming fluids in chemical and pharmaceutical plants....

I think what people are missing is that putting two pumps in the system will not automatically double the pressure in the system.... the flow-pressure operating point will reach a new equilibrium that is in fact a higher flow and a higher pressure.... depending on the configuration of the system into which the pumps are pumping. A recirculated, or even a dead-ended fuel injection fuel system incorporates a fuel pressure regulator to keep the pressure constant, so in no way will the pressure actually be doubled, but it could be if it was necessary, by cranking up the setting on the FPR.

And, you can put two pumps in parallel to gain more flow, and also gain more pressure at the same time. I know its confuing as he!!, and if you and I were at a table, I could explain it in about 2 minutes with a piece of paper and a couple of graphs.

In general, unless you want excessively high fuel system pressure with very sudden increases in pressure (e.g. - a dry nitrous system), I would go with two pumps in parallel. My two Bosch pumps are in parallel, and they operate comfortably at 58psi (4 bar). I run a dry nitrous system, but I don't need to alter the pressure, the MoTeC can simply adjust the pulse widths when it knows the nitrous is "on". I have one "master" switch that arms the nitrous solenoids, turns on the second pump, and tells the MoTeC that it is about to shift to the nitrous program..... it only actually does that when it knows the nitrous solenoids are open.

One day I was in the shop that does a lot of my work, and there was a Porsche in one bay... it had a 1973 VIN tag on it, but was mostly reinforced with tube frame, and had a fiberglass replica of a modern slant-nose body on it. The interior was two Momo seats, a lot of wire harnesses and a shift lever. It weighed absolutley nothing. Then I saw 4 Bosch fuel pumps in the nose compartment, hooked in parallel. I asked the mechanic why the Porsche had 4 pumps identical to mine, when I only needed 2 to support 800HP. He replied that the Porsche made twice as much HP as I did..... http://web.camaross.com/bb/biggrin.gif..... it had two huge turbos running at 29psi, with what looked like 5" ductwork on the discharge of each turbo.... The owner was looking for turbos that would give him more than 30psi.... I wonder how wild a ride that thing was???

[This message has been edited by Injuneer 94FormM6 (edited May 23, 2002).]</font>



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'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"

<font face="Verdana, Arial" size="2">Originally posted by rskrause:

In case it's of use to anyone else, here's short version of what my problem was and how I solved it. My SC setup had enough fuel with a 255lph Bosch in-tank and a T-Rex in-line. Stock reguator and stock lines. It did need a Kenne Bell "Boost-a-Pump" though. When I added a small (150hp) wet nitrous shot on top the FP would drop when the nitrous activated. When I removed the T-Rex, problem solved. I assume that the T-rex was limiting flow in some way, since it has a lower flow than the Bosch ay max FP of ~55psi.

Rich Krause
</font>


Location of different fuel pumps matter also. You want the better pump in front.

<font face="Verdana, Arial" size="2">Originally posted by Luna:

Location of different fuel pumps matter also. You want the better pump in front.

</font>

Makes sense! Thanks.

Rich Krause

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'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"

well i'll let all you guys know what a pair of dual intanks will handle over this summer

i plan to push them pretty hard....but most of the buick guys i talked to about them say they usually use a hobbs switch and only engage the second pump in 3rd gear

Interesting topic, and a timely one at that as I am going through the same ordeal currently...or so I think.

In a nutshell I am running a mildly built 350 (rebuilt LT4, heads, cam, FAST, Vortech, you name it) and have been having a hard time since last year getting this thing to rev and make power past 5600rpms. Currently the S/C is making right around 10psi of boost, fuel pressure is 44psi at idle and sees about a 1psi increase per/lb with the AFPR.
Last year on the dyno I was able to put down 532 rwhp at only 5600 rpms before a 60hp drop by 5700rpms. The engine should make power to 6400 at least and rev to 7K.

Fast foward to this year, I made some changes thinking my problem may have been ignition related or valvetrain float related. Take the car out this week to do some testing and all is fine until about the 5K range again where I feel a slight sputter and witness some black smoke out the tailpipe.
After logging some runs on FAST it becomes apparent that soemthing is amiss with the fuel system. At only 4600 rpms, my 50# injectors are already at 90% duty cycle and climbing fast. By 5800 rpms we are at 110% duty cycle. Obviously these things are going static and dumping fuel.

Now I am told that the 50# injectors should be good for 800 crank hp, which I shouldn't really be near, so I get to thinking that perhaps my two fuel pumps are to blame. Then I see this thread and notice that Rich and I were basically running the same system. (Intank 255lph, TRex inline).

At the advice of Precision Turbo&Engineering I have decided to bypass the TRex and just try running with the Holley 255lph in tank to see if the problem clears. I have also ordered the MSD fuel pump voltage booster to try and help out as well.

I guess my question is does it seem feasible that the TRex could be a hindrance to the 255 intank and be causing the FAST to be commanding a high duty cycle to the injectors because of poor flow? Would this also explain my inability to make power past the 5600rpm mark?

Ultimately my goal is to get this car to hit 600 rwhp, which considering where I was last year shouldn't be too hard with a little more tuning, better fuel delivery and better usage of my aftercooler. Nice thread, glad this one popped up http://web.camaross.com/bb/smile.gif

Tom

[This message has been edited by ZBass28 (edited May 24, 2002).]

Are you loggin the fuel pressure by any chance? This would be the easy way to tell.


I guess the reason I like the fuel cell idea is it will allow for you to have enough fuel on tap for even a 1000 RWHP setup and still maintain pressure and stock fuel lines.

This will allow for operation without the drop in pressure/lean condition due to big injectors opening up and the lag in the fuel system. The presure will not be achieved instantly especially since the pump is so far down stream. Use the trex pump for the fuel cell. The amount of fuel we use during a 1/4 run is minimal, so a gallon cell up front would suffice. Now if doing long distance, high speed runs then you have to upgrade the the complete fuel system.

-CAL

ZBass: Not sure if it's germane to your problem. But it reminds me of difficulty I had with some 42lb Siemans injectors at one time. When trying to run them over ~85% duty cycle they would get flaky and would usually make the car go lean, occasionally though it would be rich. IOW you could not control them at &gt;85% duty cycle. I assume they were overheating or something like that.

It does sound as though having a smaller pump downstream of a bigger pump is not a good solution when you need high volume and not high pressure though. As I said before, I am supporting 733rwhp with a single 255lph intank, stock lines, stock regulator. The same setup did NOT work with the T-Rex installed. I am using the Kenne Bell "Boost-a-Pump" as well. The system is inadeqaute with the BaP disconnected. It increases voltage to the pump to 17 volts when under boost. This is much easier and cheaper than trying to add another pump in parallel, though if I take this thing any further it seems as if that will be needed.

Rich Krause

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'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"

I will be adding the MSD version of the boost-a-pump tonight. The bypassing of the Trex has been done. Hopefully this will solve my problem in the same way that yours got better. There should be no way I am maxing out these injectors just yet.

I'll let ya know if this helps, thanks for the info guys.

Z Bass, did the fuel pump bypass of the Trex work? I really need to know because I am having the same problem. I seem to run out of fuel at 4,000. The car just won't pull any more. It is like I hit the breaks. I need to know if it is in my programming or in my inline fuel system. Keep us posted as I know I am not the only one with this problem.

ZBass:

By my calculations, a 50# injector probably isn't good for any more than about 700crankHP on a power adder engine....

Just plugging in some values...

-710crankHP
-0.53#/Hr BSFC
-85% duty cycle
-53.5psi (43.5 + 10)

... a 50# injector is at its limit. You might want to look at a little more pressure, or a larger injector. I run 64's at 58psi for slightly less than 800crankHP (less than 70% duty cycle).

With the gradual pressure rise, I would think you would want pumps in parallel, rather than in series. I saw an intank pump plus a T-Rex in parallel make over 800crankHP at a fairly high fuel pressure with 83# injectors.

Personally, I don't even see why those multiple inline external pumps are necessary. Rich said he's making 730+ rwhp on a single 255 lph intank, and I know Derrick Redd is making 550ish on the stock bottom end with a single 255 lph intank. My friend has a Vette with a few inline external pumps. When one goes out, the total system pressure drops to crap. It's completely retarded. I don't see the point, really.

All you need is a single bad-ass intank, or if you feel the need to: a single bad-ass external - friend has a 1000 hp-compatible external Aeromotive on his Mustang which sounds like a chainsaw http://web.camaross.com/bb/smile.gif All of this multiple external inline stuff is for the birds.

Mike

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Part of it has to do with the use the car sees. In a street car, that has to operate at very low fuel demand, a "1000HP pump" is going to be recirculating an awful lot of fuel... that fuel gets heated up in the pump, heated up in the lines when it passes the exhaust system, and heated up in fuel rails. Heat it up enough, and you are going to generate excessive vapor loads in the tank, and eventually heat up the entire fuel supply. I have seen it happen, and it required a fuel cooler to correct. More weight.... more plumbing.

A pure track car doesn't have this problem, and can handle the short periods of high recirculation. A "chain saw" sound might also be more acceptable on a track car than on a street car..... http://web.camaross.com/bb/smile.gif

A properly sized fuel system, with the correct fuel pressure regulator will not vary in pressure when the extra (parallel) pump is turned on or off. Mine doesn't. You might see the needle on the gauge "twitch" one psi or so at most, but the pressure stays in complete control.

Fred: Thanks for the run down on the injectors, looks like I will need to address that and look for some slightly bigger ones.

For those that wondered whether bypassing the T-Rex has helped I honestly can't say yet. I haven't had a chance to really hammer on the car as 2 new problems have surfaced, one stemming from me and a buddy apparently running the MSD fuel pump voltage booster incorrectly and possibly frying the sender in the tank for the fuel level gauge. Might be the time to drop the tank and put the better 255lph Walbro in instead of the standard 255lph that I currently run.

Either way, with Fred's explanation it looks like I will be running out of injector.

<font face="Verdana, Arial" size="2">Originally posted by ZBass28:
Fred: Thanks for the run down on the injectors, looks like I will need to address that and look for some slightly bigger ones.
</font>

You don't want to be running 100% DC for long but there is nothing wrong with it.

80 to 85% is a good range for prolonged use but for a street/strip burner 100% is fine. We aren't normally doing high speed runs with these cars. People go hogwild with injectors alot of the time when then aren't needed.

That I understand...

Currently though I am seeing near 100% duty cycle just barely over 5000 rpms. By 5800 it was at 110%.

Also, not sure how this factors in to Fred's equation but the injectors were flow tested at 44.7-44.9 lbs I think at 80% duty cycle.
I don't want to go too big but I would like some nice headroom to work with.

Two Aeromotive 1000hp EFI fuel pumps in parallel. One pump will serve as the primary pump and the secondary pump speed will vary based on engine rpm. Both pumps are controlled by their own Aeromotive billet fuel pump controller. -10 AN fuel feed line, and a -08 AN fuel return line.

http://www.montygwilliams.com/fuel_pumps_filters.jpg

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Hey guys, what about inline pumps that are higher than intank pumps.

Say, a 255lph intank, with a 405lph inline. Will that cause a problem?

<font face="Verdana, Arial" size="2">Originally posted by SprayedZ28:
Hey guys, what about inline pumps that are higher than intank pumps.

Say, a 255lph intank, with a 405lph inline. Will that cause a problem?</font>

From the experience Rich had, id say you'll be fine since the inline flows more than the intank.