Stock Fuel Pump enough for surge setup?
 

Hey guys, anyone know if stock pump is sufficient as a feeder to the surge tank?

Car will be running the following:

-2.5Liter Aluminum Surge Tank - 6an In/Out/Overflow and 8an Feed to High Pressure pump

-Feed from tank to surge 6an, surge back to tank 6an, return to surge tank 6an

-Fuel Lab 42401 200GHP High Pressure Pump
-Fuel Lab Electronic Feedback Regulator to control pump speed (minimizes return flow)


Pretty simple setup. I'm just not certain about the volume of fuel from tank to surge. Is it even possible to drain a 2.5Liter surge? I'd imagine you'd have to be on throttle for SERIOUS time like 5th gear pulls back to back to back


What are your thoughts on in tank pump?

i feel like this is one of those math problems where a train leaves New York traveling X MPH, and a train leaving Washing DC leaves at the same time traveling X MPH, where would they crash?

basically how many seconds of WOT will it take to drain 2.5 liters, and how much fuel would the stock pump push into the surge tank during that time.

what is the stock pump flow at no restriction? vs what is the max fuel flow you will need at you power levels?

Going back over these numbers again hold on thanks!

Ok heres the actual calculations:

Fuel Demand @ WOT @ 1000rwhp (calculated using BSFC, Fuel Pressure Drop, IDC, Injector Size)
127 GPH
429 LPH
7.98 LPM
0.13 Liter/Second

Lift Pump Capacity (Refill Potential)
Walbro 255 @ 0 PSI
285 LPH
4.75 LPM
0.08 Liter/Second

Surge Tank Capacity
1.5 Liter Tank
11.27 Seconds to Drain @ WOT
18.75 seconds to Refill (OFF THROTTLE)

Figures:
-0.133 liters of fuel consumer per second @ WOT
0.08 liters of fuel restoring (constant, off or on throttle)
*-0.05 Liters Per Second NET FUEL CONSUMPTION (without starvation and WOT)

If fuel consumption at WOT of 0.133 liters per second, while refilling at 0.08 liters per second, -0.27 liters utilized in 5 seconds.

-0.53 NET loss @ 10 seconds
-0.80 NET loss @ 15 seconds
-1.06 NET loss @ 20 seconds
-1.33 NET loss @ 25 seconds


Conclusion:
At WOT, with no starvation present, maximum WOT duration of 25 seconds permitted before STALL

At WOT, with max starvation present, maximum WOT duration of 11.27 seconds permitted before STALL



So the grey area is, depending on how much starvation is present, the refill time before you can get back on the throttle varies. But what this does show is at least 11.27 sec worst case scenario of constant fuel at a demand of 1000rwhp (that's with literally no fuel pickup or return).


Is this an acceptable amount of reserve capacity for a surge tank?

If a pump could be had that pushes 400LPH (like a walbro 400), this would give only a net loss of -0.02 Liters per second! But a walbro 400, at 0psi is going to explode the surge tank with like 1000lph :) :) :)

- I wouldn't feel comfortable with a lift pump that could not supply the volume of the engine at WOT.
- A lift pump that overfills the surge tank is not an issue as the surge tank should return to the main tank anyway.
- The pump speed of the lift pump could be controlled just like the pressure pump. And, FWIW, you don't need the high dollar Fuelab regulator to run their pump with the ECU you're going to run. Your ECU can send the PWM signal to the Fuelab pump to control it directly.

^^ agree, you should overflow your surge tank so you NEVER run the risk of starvation

Hey Chris,

thanks for the insight, the Walbro 400 would probably totally dominate the Fuel Lab pump at 0psi in the tank. I've just been reading that if there's overkill on the in-tank pump, it will pressurize the surge and add pressure to the system. And I do see what you're saying, that walbro could be controlled with PWM as well right? I just like to keep it as simple as possible and not mess with fuel pump speed on the tank if possible.

Do you think Walbro 400 will be okay? Maybe it wouldn't be a bad idea to run stock 5/16ths feed to the surge, and then for overflow from the top of the surge use a -8an back to the tank to ensure that it doesn't backup with pressure

Also have a aeromotive 340lph pump



And regarding the PWM, yea, I'd love to use the PWM off the ECU and avoid the extra expense of the regulator, so long as figuring out the most efficient duty cycle map doesn't take more tuning time in labor cost than the extra PNP cost of the regulator

As long as there isn't a restriction in the return between the surge tank and the main tank, you won't build pressure in the surge tank. On a 1000hp build, I would do -8 feed to the surge tank at a minimum. No reason to restrict the flow going into the surge tank. -8 in and -8 return with a -10 feed to the pressure pump. That's my thoughts on minimum sizing.

Amen, problem solved will do!

Why is having pressure in the surge tank a problem? I'm doing this on purpose to maximise my efi pump and it works.

I agree. Pressurizing the inlet of the pressure pump will help its efficiency. You'll need a second bypass regulator for the surge tank though. Guess it comes down to what is the simplest solution that works?

This is all new to me, but as long as the preset fuel pressure doesn't drop off in the event that the walbro cavitates/starves I guess it doesn't matter at all.

I've just read something of guys using large lift pump, in respect to their overall fuel consumption/delivery pump, and not being able to get the fuel pressure down under 60psi base etc. This is more than likely from not having a large enough return line right?


And ya know what, maybe it is a cool idea to pressurize the surge tank, because even if the lift/main tank is cavitating from heat etc, the higher pressure in the surge will keep boiling point up!


Ideally though, I'm simply looking for the least amount of plumbing, the least amount of wiring, and the least amount of potential fail points. So, if a Walbro 400 in the tank works, feeding a small 1.5L surge, feeding the big pump, thats more than enough for me!