would be super easy for me to install. I have a 2psi Hobbs switch I can install in my boost block to activate the pump. My issue is controlling fuel pressure with the 2nd pump activated and the tune data being way off when the 2nd pump kicks on.

 

I don't think you would need this fitting if running the pumps in question is series. I have a single Walbro 450 in tank pump and it holds pressure at the fuel FPR for a long time after shut down. I interpret this to mean it has it's own working check valve. I also wonder about controlling a fuel pressure spike when the second pump comes on due to possible restrictions of the second inline pump.

 

You missunderstood. I was only bringing up the fitting as a example as any restriction even if its small on the exit pressure side of the pump effects pump flow easily and considerably depending on the restriction. I however believe a dead pump is MORE of a restriction than a simple check valve.

You are correct that just about any INtank fuel pump has an internal check valve. However fuel rail pressure being held when the key is off is fully dependent on the fuel pressure regulator and the pump. For example my non stock Aeromotive bypass regulator will not hold pressure with the key off, it actually drops like a rock. They are designed to do this as they dont have strict EPA regulations that the OEM stuff has to abide by.


So basically what Ive read is that with the pump inline off it creates a restriction (intank pump works harder to push fuel through) but you dont notice because the pump is making the same rail pressure that you have your regulator set to, pump is working harder to maintain the same pressure and it will get worse as fuel demand increases (since key off no fuel is consumed, or at idle its very low). Then once that second pump activates that restriction is gone, so that restriction disappears basically and thus flow is increased just at the intank pump ALONE without any help from the inline pump. so theres a flow difference there that no one can account for. Then add this...

1.) Say the pump flow is 400lph at 60psi with the 450lph intank pump. That means by itself the pump flows 400lph at 60psi. Pump flow curves are different for both the 450 intank and the 380 AEM. So flow charts need to be overlayed to know what your getting.

2.) the 2nd inline pump lets say is the same pump but external so it flows the same 400lph at 60psi. But since these pumps are in series and working together the pressures split. So the pumps really only see 30psi each to make the same 60psi of fuel pressure. But since the pumps are only seeing 30psi the pump flow increases even more! So say each pump flows 450lph at 30psi. So that means instead of getting 400+400 = 800lph at 60psi your really getting 450+450 = 900lph of flow at 60psi. The nice thing is that the fuel pressure will not drop like a rock as pressure increases. So you actually gain twice the fuel pressure capability but also gain 10-40% in flow as well since both pumps work half has hard to create the same pressure. Factor in the pressure loss of pushing fuel through a dead pump, + that same loss restored once activated, + the fuel pumps flow increasing as pressure decreases once both are activated. I'm sure the FPR is going to be doing some funky *** **** once both pumps are activated vs only one and pushing through a dead pump.

Its these reasons I'm hesitant to forge ahead. But I will do it in a heartbeat if I run out of pump currently as I can deal with it. Since my Self learning Fitech will adjust pulse width to manage my commanded AFR.

 

I can't remember the setup and I'm not going to read it. If it's a stock one and the pressure is below the setting with one then you have a restriction. If the pressure with both is higher than set then the regulator is to small. If you set a correctly sized regulator it will not let the pressure go higher with the second pump on.

 

Not sure I'm following the first part.

The regulator is a aeromotive 13301 https://www.summitracing.com/parts/aei-13301 and its good for supposidly 250 GPH flow as a carb setup (light spring) which means it will support the same at EFI pressures. I am not sure if the pressure will creep with the 2nd pump installed until I test it. The pump install would be pretty easly but I would need to make a new line (shorter) to install.

I basically wanted to see if the walbro 450 would keep up if I lowered fuel pressure from 58 to 43psi. This lowers the flow rating of my injector from 72lb at 58psi to 60lb at 43psi, but the flow of the 450 in that range increases a good bit. I will either run out of pump or injector (i'm thinking injector if I'm pushing the HP I want to) so worst case is I run both pumps in series and bump fuel pressure back up to 72psi for the 12lb increase and be done with it. If I run both pumps I could easily run even higher pressures like 72psi base pressure and make the injectors over 80lb since I wouldnt be stressing the pumps at all. I would rather not have both pumps running continuously due to fuel heating as stated and since my car is street driven it see's considerable run time in the hot months only.

If I go though the work of testing and installing the 2nd pump I would leave my regulator at 43psi and see what pressure increases happens from just the 2nd pump install. I might do it honestly just for fun as I have a few months of not being able to drive the car. I personally think there will be a bump in fuel pressure just due to the 10-40% of extra fuel flow.

 

A regulator that can handle 600lph should hold the set pressure with just one 255 walbro or two just the same. Every regulator has to handle the most fuel at key on or idle over what it does when the motor is doing work and reducing the amount of fuel returned by injecting it to burn.

The lower pressure you run as a base the less the fuel will heat from the pumping. Other sources of heat from the engine bay will still heat it the same. Your pump will also last longer and flow more, so I'd choose 3 bar over 4 bar every time I can.

 

I agree with everything you said.. But the flow pressure set at 400lph will be different than at 800lph. thats a TON more fuel flow it will have to bypass.

So here are some of the facts about each pump ( I have attached screen shots of each pump flow vs pressure as well. These pumps are actually very closely matched and should work well together!

My math dictates the following @ 43psi base pressure
walbro 450 = 0-30psi =455lph/120gph, 40psi flow drops to 430lph/113gph
AEM 380 = 0-40psi = 425lph/112gph, 45psi flow drops to 420lph/111gph (no check valve going to be used)

So if both pumps run we are talking about 43psi base pressure so each pump should see about 21.5psi of fuel pressure lol. That means the max flow total will be about 880lph or about 232GPH!! Thats right around the MAX flow of my regulator supposidly.

The more and more I look at this the better it sounds to run dual pumps in series at a lower base fuel pressure. But it will allow me to bump up base pressure to 58psi and basically not affect fuel flow at all even at 12psi of boost. 70psi of fuel pressure means the pumps are only seeing 35psi each. However theres no need to overcomplicate the system and if the 450 on its own will work just fine then theres no reason to add the extra complexity and amperage draw of the 2nd pump.

 

The point was if the regulator is rated correctly the only way it should not hold the set pressure is if you go over that number or because the change from the reference port.

I wouldn't run Aeromotive if it was given to me for free, but that is just because of the bad luck I've had with it before. Others probably only run them and have no issue, that is fine as I'm not saying they build junk. They just don't build to specs that match my luck, LOL.

I know if you get a Weldon regulator, it will hold the pressure it's set to as long as you don't feed it more than it's designed to handle.

I don't think the load works quite that way as the first pump will always have more load and be working longer. You could test this out though if your monitor the amps of each pump. First get a base of both pumps at free flow and at the set pressure. Then put them in the car and see with the first one does with the second one off and finally what they draw with both of them running.

 

Resurrecting this thread. Customblackbird how did the 2 in series work out? Did you see if turning both pumps on vs just the 450 changed your ability to maintain base fuel pressure/change tune at idle/low engine speeds? Did you wire them both to run all the time or the 380 on a hobbs switch? Plumbing mine now and need to make some choices on how to max out the Deka 80's.

 

I never got around to doing it honestly. I’ve been staying under the max power of my 60lb at 43psi injectors or 72lb at 58psi.

 

Well I'm about to try it on my build. I'll add feedback when I get that far. Don't hold your breath though, my projects move slow (busy). lol