Here's an easy to make surge tank

[Pop N Wood]

Low pressure usually means carb type pressures, maybe 6 to 12 PSI. Fuel injection, well I don't know what pressure fuel injectors need to operate at but isn't it 35-60 PSI.

 

Don't confuse "pressure" with high or low flow. They are two physically different pumps.

 

One pump just keeps the reservior full. It doesn't pressurize the cannister cause the cannister has a return like back to the tank that won't allow that.

 

The second pump, the one drawing off the cannister and feeding the engine, has to the right pump for the engine you are running. If it is carbed it will be a low pressure pump, fuel injected it will be high pressure.

[Careless]

Low pressure usually means carb type pressures, maybe 6 to 12 PSI. Fuel injection, well I don't know what pressure fuel injectors need to operate at but isn't it 35-60 PSI.

 

Don't confuse "pressure" with high or low flow. They are two physically different pumps.

 

One pump just keeps the reservior full. It doesn't pressurize the cannister cause the cannister has a return like back to the tank that won't allow that.

 

The second pump, the one drawing off the cannister and feeding the engine, has to the right pump for the engine you are running. If it is carbed it will be a low pressure pump, fuel injected it will be high pressure.

 

so again, does the low pressure pump have to be one that flows more than the high pressure pump to keep the system going without introducing air?

 

that was my main concern, because I know the difference between flow and pressure, but the reservoir was posing a problem for me in the event that it runs dry.

[blueovalz]

Perhaps this will help. In the simplest terms, the low pressure pump flow should be = to, or > than the high pressure pump flow. In practice though, your low pressure pump will be happily pumping away at pretty much optimum (maximum) flow due the the return line back to the tank, whereas the high pressure pump, even though it is also happily pumping away, depending upon engine loading, will be returning some of the fuel NOT back to the tank, but instead, back into the reservoir. When this happens, some of the fuel being removed from the reservoir is being returned back to the reservoir (again, the amount depends upon engine loading). So in reality, depending on actual fuel usage, you could find that in practice, the low pressure pump could be rated at a lower flow value than your high pressure pump, and still provide uninterrupted fuel supply to the high pressure pump.

 

You could even go so far as to be "marginal" in that under high load conditions, the high pressure pump pulls the fuel level of the reservoir down a certain amount that will be immediately recovered by the low pressure pump once the engine loading is reduced (for example, at idle or light cruising mode).

 

So to answer the question, you should have a low pressure pump flow capability that is = to, or > than the fuel usage at the motor's highest power output. If the high pressue pump rated flow is excessively greater than what could be used by the motor, than you will skew your requirements for the low pressure flow IF you are only comparing pump to pump, and not pump to fuel usage.

[Careless]

Perhaps this will help. In the simplest terms, the low pressure pump flow should be = to, or > than the high pressure pump flow. In practice though, your low pressure pump will be happily pumping away at pretty much optimum (maximum) flow due the the return line back to the tank, whereas the high pressure pump, even though it is also happily pumping away, depending upon engine loading, will be returning some of the fuel NOT back to the tank, but instead, back into the reservoir. When this happens, some of the fuel being removed from the reservoir is being returned back to the reservoir (again, the amount depends upon engine loading). So in reality, depending on actual fuel usage, you could find that in practice, the low pressure pump could be rated at a lower flow value than your high pressure pump, and still provide uninterrupted fuel supply to the high pressure pump.

 

You could even go so far as to be "marginal" in that under high load conditions, the high pressure pump pulls the fuel level of the reservoir down a certain amount that will be immediately recovered by the low pressure pump once the engine loading is reduced (for example, at idle or light cruising mode).

 

So to answer the question, you should have a low pressure pump flow capability that is = to, or > than the fuel usage at the motor's highest power output. If the high pressue pump rated flow is excessively greater than what could be used by the motor, than you will skew your requirements for the low pressure flow IF you are only comparing pump to pump, and not pump to fuel usage.

 

I see.

 

ok, cause the picture had originally confused me a bit regarding the flow/pressure balance between the two pumps.

 

Thanks for clearing that up

 

Now back to the Receiver Dryer.

 

I've pulled the one off my S14 front clip that I sawed in half to fit in my van (fun stuff!). It has a glass viewing hole, a sensor, two holes, and a bolt that is fastened on as well. A total of 5 holes if I remove the glass (which i think i will keep, so i can see if i have fuel flow =) and I can see metal disc inside that has small holes in it as well.

 

It seems to be about the same size. Should i remove this metal disc? cause I'd imagine it would be pretty damn hard. LOL.

 

 

EDIT:

 

also, what's a good fitting size to tap into this thing, for say, a 300 - 500 hp engine.

[strotter]

Glad we got the high pressure/low pressure thing figured out.

 

Careless, the metal disk can stay, but any desiccant pellets and filter or bag has to go. The disk is there to restrain the desiccant and filter, so you'll find them "under" it. And of course the whole thing needs a thorough rinsing with something voluble that'll put the a/c lubricant into suspension. I used mineral spirits then acetone, not for any chemical reason but 'cause I ran out of mineral spirits. If you have a good sniffer you can smell the esther lubricant, even over the other smells.

 

As for fittings, you're only limited by what will fit. I ended up using 3/8 i.d. for everything, though note that there are different threads available for the same i.d.; the smallest I could find at OSH was 1/2" npt.

[Careless]

awesome, I'll clean the unit up on the outside using a wire wheel later today, and I'll inspect what kind of holes i need to make. I think i might have enough so that I dont even have to make one.. but I'd like to relocate one to the bottom anyways.

 

Heck, I might as well buy a small fuel pressure guage to shove into one of the holes so I can tell how much pressure I have in the 'voir too

[Doug71zt]

You won't have any significant pressure in the surge tank, because of the return line to the tank.

[MrFancypants]

also, what's a good fitting size to tap into this thing, for say, a 300 - 500 hp engine.

 

3/8" would be plenty. You could even probably get away with 5/16". 1/2" would be total overkill.

 

This idea is a really great idea, by the way! Very resourceful!

 

 

 

- Greg -

[Careless]

You won't have any significant pressure in the surge tank, because of the return line to the tank.

 

good point.

 

 

i guess i'll have to find a bolt to block off those holes =)

 

but the glass eyelet on this receiver driver is a neat tool to check if fuel actually is in there

 

im gonna drill it out for 3/8'ths for now, and if i need to go bigger, I will. Im just at my dads house who has a drill press, so I gotta get it squared no, or i wont get it done for a while.

 

 

not like i will be using it any time soon anyways, but i want to be able to do something worthwhile with my time.

[Tony D]

My feeder/booster pump for years was the stock 240 electric pump!

 

So that means you can get away with a VERY small 'booster' pump. Especially if your EFI return line is coming back to the surge tank.

[BLKMGK]

FWIW, Jegs and Summit sell radiator overflow tanks that can be used for this. I have an aluminum one on my car that might even hold more than a dryer. Wasn't super expensive - here's one http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_225620_-1

 

That kind of thing might be even easier to adapt. Just be careful as neither of these solutions have anything to prevent aeration. Most of the stuff I've seen purpose built for this has had something to help separate air. I too have wondered how best to get EFI going on my car and a surge tank type deal seems like the way to go with my fuel cell...

[Careless]

FWIW, Jegs and Summit sell radiator overflow tanks that can be used for this. I have an aluminum one on my car that might even hold more than a dryer. Wasn't super expensive - here's one http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_225620_-1

 

That kind of thing might be even easier to adapt. Just be careful as neither of these solutions have anything to prevent aeration. Most of the stuff I've seen purpose built for this has had something to help separate air. I too have wondered how best to get EFI going on my car and a surge tank type deal seems like the way to go with my fuel cell...

 

do you know of any check valves that one could use for the air-release?

 

I have 4 holes on the top of my 240sx s14 dryer. 2 of them are already tapped. One was for a pressure sensor, and the other was blocked off (perhaps they are mounted differently in JDM cars, so they make two sensor bungs)

 

I could now tap one for rail-return, and one for aeration. Any ideas?

 

EDIT:

how about this, with a crank-case vent filter:

 

http://cgi.ebay.com/LINDE-REVERSE-FLOW-CHECK-VALVE_W0QQitemZ180080986141QQihZ008QQcategoryZ67059QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

[strotter]

BLKMGK, that looks like a good solution. However, I noted that the upper fitting appears to be set into a boss at the top, leading me to wonder what the wall thickness is on the unit. You're going to have to tap two more fittings into the top, aren't you? I wouldn't be comfortable unless there were at least a couple of threads worth of aluminum there...

 

Careless, I think BLKMGK is talking about air bubbles "mixed" with the fuel so that it enters the high-pressure pickup at the bottom, where it'll get sent out to the injectors. You don't really need to separate the air out - any air that finds itself at the top of the reservoir is going to "go with the flow" back to the tank via the low-pressure return anyway: you just need to keep it away from the bottom of the tank. It's a concern, especially with a reservoir like this one, 'cause there's a torrent of fuel being squirted into the reservoir from the high-pressure return at the top, straight down, ensuring that if there's an air-pocket at the top it'll shoot a stream of bubbles all the way to the bottom where they'll get picked up by the high-pressure inlet. To a lesser extent that'll be true of the low-pressure pump as well. This will be especially true at idle, when the return-line is flowing at its' maximum. At full demand, the high-pressure return will be flowing just a trickle (because all the fuel will be exiting via the injectors and not returning to the reservoir, assuming the high-pressure pump isn't radically oversized for your engine).

 

I think the best solution is to guarantee that an air gap never forms at the top of the reservoir. The only way *that* can happen is if the mass-flow out exceeds the mass-flow in. Hey, let's make an equation!

 

(Lo=Low pressure system, Hi=High Pressure system, "in" & "out" means in & out of the reservoir)

 

MassFlowIn >= MassFlowOut

 

MassLowIn + MassHiIn >= MassLowOut + MassHiOut

 

but ... MassHiIn = MassHiOut - MassInjectorFlow (at max demand)

 

so we substitute that in and we get...

 

MassLowIn + MassHiOut - MassInjectorflow >= MassLowOut + MassHiOut

 

and let's cancel MassHiOut on both sides,

 

MassLowIn - MassInjectorflow >= MassLowOut

 

and then let's move some things around,

 

MassLowIn - MassLowOut >= MassInjectorFlow

 

and then if we say that MassLowOut can = "0" at max demand,

 

MassLowIn >= MassInjectorFlow.

 

Which means that so long as the low-pressure pump can keep up with the max demand of the injectors, you'll never form an air bubble on the top of the reservoir, and therefore never have aeration.

[Careless]

BLKMGK, that looks like a good solution. However, I noted that the upper fitting appears to be set into a boss at the top, leading me to wonder what the wall thickness is on the unit. You're going to have to tap two more fittings into the top, aren't you? I wouldn't be comfortable unless there were at least a couple of threads worth of aluminum there...

 

Careless, I think BLKMGK is talking about air bubbles "mixed" with the fuel so that it enters the high-pressure pickup at the bottom, where it'll get sent out to the injectors. You don't really need to separate the air out - any air that finds itself at the top of the reservoir is going to "go with the flow" back to the tank via the low-pressure return anyway: you just need to keep it away from the bottom of the tank. It's a concern, especially with a reservoir like this one, 'cause there's a torrent of fuel being squirted into the reservoir from the high-pressure return at the top, straight down, ensuring that if there's an air-pocket at the top it'll shoot a stream of bubbles all the way to the bottom where they'll get picked up by the high-pressure inlet. To a lesser extent that'll be true of the low-pressure pump as well. This will be especially true at idle, when the return-line is flowing at its' maximum. At full demand, the high-pressure return will be flowing just a trickle (because all the fuel will be exiting via the injectors and not returning to the reservoir, assuming the high-pressure pump isn't radically oversized for your engine).

 

I think the best solution is to guarantee that an air gap never forms at the top of the reservoir. The only way *that* can happen is if the mass-flow out exceeds the mass-flow in. Hey, let's make an equation!

 

(Lo=Low pressure system, Hi=High Pressure system, "in" & "out" means in & out of the reservoir)

 

MassFlowIn >= MassFlowOut

 

MassLowIn + MassHiIn >= MassLowOut + MassHiOut

 

but ... MassHiIn = MassHiOut - MassInjectorFlow (at max demand)

 

so we substitute that in and we get...

 

MassLowIn + MassHiOut - MassInjectorflow >= MassLowOut + MassHiOut

 

and let's cancel MassHiOut on both sides,

 

MassLowIn - MassInjectorflow >= MassLowOut

 

and then let's move some things around,

 

MassLowIn - MassLowOut >= MassInjectorFlow

 

and then if we say that MassLowOut can = "0" at max demand,

 

MassLowIn >= MassInjectorFlow.

 

Which means that so long as the low-pressure pump can keep up with the max demand of the injectors, you'll never form an air bubble on the top of the reservoir, and therefore never have aeration.

 

I'm at work so i haven't the time to read the equation, however - i will once i get home. thanks

 

question though. since my 'voir has 4 inlets at the top, can i instead, drill a hole through one so that I can stick a pickup tube in there, and have that as the main pump pick up, rather than have the return fuel line dropping gasoline on the lower barb fitting?

 

would that eliminate the air to any degree?

[strotter]

Careless wrote:

question though. since my 'voir has 4 inlets at the top, can i instead, drill a hole through one so that I can stick a pickup tube in there, and have that as the main pump pick up, rather than have the return fuel line dropping gasoline on the lower barb fitting?

 

I don't see why not. It just seemed easier to me to tap the bottom, but whatever works!

[Careless]

I'm at work so i haven't the time to read the equation, however - i will once i get home. thanks

 

question though. since my 'voir has 4 inlets at the top, can i instead, drill a hole through one so that I can stick a pickup tube in there, and have that as the main pump pick up, rather than have the return fuel line dropping gasoline on the lower barb fitting?

 

would that eliminate the air to any degree?

 

would that eliminate the chances of air getting into the system though, as it would have to syphon from a pool of gas sitting at the bottom rather than funnel the gas dropping in and splashing around as you said in a post earlier?

 

I'm probably gonna end up using the stock 280z FI fuel pump to pump in, and the new pump that i will get will pump out.

 

both will have a higher pressure than 30 psi though, so is that going to be a problem =/

 

?

 

i got the fittings yesterday, but now i have to drill out the holes and tap them, and the tap/die set i have has no such fitting. only 1/4 NPT. =(

[strotter]

Careless wrote:

would that eliminate the chances of air getting into the system though, as it would have to syphon from a pool of gas sitting at the bottom rather than funnel the gas dropping in and splashing around as you said in a post earlier?

 

Well, nothing will eliminate air getting in, I suppose, but minimizing the chance that it will is as good as you can hope for. If the high-pressure system is pulling out more fuel than the low-pressure system is pushing in, the internal pressure will drop below ambient pressure and air will enter the system via the low-pressure return line, assuming the return is exposed to air in the tank - which I believe it is in the original Z tanks. Putting the pickup at the bottom of the surge tank is going to be the "best case" design, whether you pick the fuel up via tube or hole in the bottom.

 

Careless wrote:

both will have a higher pressure than 30 psi though, so is that going to be a problem =/

 

Remember, the low-pressure pump is only going to see, well, low pressure. Likely only 1 or 2 psi, depending on friction losses. As far as that pump's concerned, it's just shooting fuel around a short loop of hose and then back to the tank, so it's going to be moving a lot of fuel. The high-pressure pump, however, will be pushing against the pressure regulator up front, so will see whatever pressure the regulator is set to, somewhere between 40 and 50 psi, and will therefore pump only some fraction of its' maximum capacity.

[BLKMGK]

The overflow tank I linked is fairly lightweight. I've got one on my Z so I'll try to take a look at it - it may have a bung welded on it for the fittings.

 

FWIW, I built something somewhat like this as a water resevoir for my computer - the purchased ones in plexi kept cracking. Anyway, the volume of the tank isn't as big as I'd like it and the return is at the top. Until I filled that sucker near to the top the water comping out the bottom was FILLED with air bubbles! It must have been really churning in there - I used about 6inches of 3inch pipe. Obviously not a fuel system but even in this low volume app I was surprised at the amount of foam I generated. I wouldn't want a mixture like that being fed to my injectors for sure!

[strotter]

BLKMGK wrote:

a water resevoir for my computer

 

you just gotta tell me about this.

[Matt K]

Just out of curiousity, would it be bad to have a normal EFI high pressure pump filling the surge tank & another one (slightly more powerful) after the surge tank? My application is a 240SX (sorry, my 280ZX is stock for now!) with a VERY modified SR20DET & I'm not comfortable using only one pump at the high altitude I live in now (~5500 feet) with the crappy 91 octane they serve up as premium here. I'm currently using a Z32TT fuel pump & am afraid to push the car hard (has previously made 522 rwhp back in Okinawa with a single Walbro 255L pump).