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Lift Pump selection and Amperage draw

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Hello everyone,

I am building a S13 240SX with a LS3 (ish... 6.2L L92). I have found a massive leak in my fuel tank and instead of sourcing a new one or "good" condition used one, I am just going to install a fuel cell, with Radium Fuel Cell Surge Tank. I will have the opportunity to put multiple pumps in. etc. etc. I am going to be on E85. Since I am N/A for now, I am just going to run a single Walbro 450. Per Radium's recommendation, they say you should run a lift pump that is approximately 50% of the primary pumps, which would be 225 LPH (or a 255LPH to keep it simple). I am also running a Nexus R5 and don't really want a fuel pump that exceeds one of the 8A HCO's, because I only have one left and I also don't want to have to upgrade EVERYTHING once I do go forced induction. Would a 255 be sufficient in feeding a surge tank that has potentially two 450LPH fuel pumps?

As of right now, I have one 25A HCO for the primary pump and would like to use an 8A HCO for the lift pump. If that doesn't seem feasible, I could always run a 450 and a relay triggered by a DPO for the lift pump until I get Haltech's PD16.

I hope this jumble mess of a post makes sense...

Hi Kevin,

What you are looking for with a lift pump is volume and not pressure, so you may find (I haven't used the Walbro 255 so I do not have any "real world" data) that the 255 feeding the surge tank only, and not having to pressurise the fuel system may have a quite low current requirement. Otherwise, have a look for a HVLP fuel pump, such as pumps designed for high power carby installations.

As to whether it is capable of keeping up with the two 450's, that depends on the amount of return fuel in the system assisting in filling the surge tank, and the length of time that the vehicle spends at the maximum fuel burn. If it is just short squirts such as drag racing, drifting or road use, then it it possibly going to be okay, but if the car is constantly in the maximum fuel burn area, then the lift pump may not be able to keep up with the feed requirements and lead to fuel starvation.

Thank you for the quick response. I think I will just run the lift pump off a relay for the time being and move it to a 25A in future when I get the PD16. Might as well just match the primary pumps with the lift pump.

Are you sure the lift pump was 50% and not 150% of the pressure pump flow?

With the former, the pressure pump would rapidly lose pressure as the surge tank ran dry, whereas with the latter it would keep the surge tank full and have sufficient flow to ensure it's bled of any air in the system.

As Steve said, running with little, or no, pressure head the pump will have a much lower current draw and higher flow rate, than if it was presurising the system to the rail pressure.

However, if you're using a fuel cell, have you considered using an in-tank assembly with an in-build 'surge tank' around the pick-up? If you have a dual, or triple, pump type you can run one as an initial pressure pump, avoiding the lift pump and external surge tank?

Forgot, is the vehicle using a 'dead head' fuel system, without a return, or a recirculating type and, if the latter, return to surge tank or fuel tank? If it's the former it's more important to avoid picking up air as it's not self bleeding, like the latter.

Current draw should be significantly lower at near no head pressure. There are a few web sites which have published flow/pressure/Current draw of a range of common pumps if you search.

I plan on using the Radium FCST which is an in-cell surge tank system. I am running a return style fuel system. The Radium FCST returns fuel into the surge tank.

The example Radium gave was if my injectors require a flow of 800 LPH I need a lift pump that can supply 400 LPH to the surge.

That's basically what they said in an email to me, but here is a blog post from Radium about fuel pump selection that says the same:

http://www.radiumauto.com/Blog/Post/Selecting-Surge-Tank-Fuel-Pumps-101

If I am running off of fuel pump data I have found online a Walbro 450 will still draw around 14A at 13.5V at 0PSI. Which leads to needing 2 8A HCO or 1 25A HCO, of which I only have one potentially spare 8A HCO to use.

So they do, but if you do that, rather than match the flow of the pressure pumps, make sure you have something in place to monitor the rail fuel pressure.

I plan on putting an analog gauge at at least one rail end and one sensor at the regulator.