Hiboost

iTrader: (9)

So I'm aiming for 550 whp on the STM Mustang Dyno which is just over 700 crank HP. We're using a Fuel Labs fuel pump with about 400 LPH capacity feeding off a surge tank from MAP along with one of those new Fuel Lab electronic fuel pressure regulators that is supposed to work on a demand based setup to ramp up power to the pump only when needed. That part should work fine...

Right now the stock fuel pump is still in the main fuel tank as it was fine supplying fuel to keep the surge tank filled at 350-400 whp levels. I know the stock fuel pump is rated for around 210 LPH @ 43 psi and gives out at 380 whp or 500 crank HP, but that is when pressurizing the rail with it.

The question is, at what point does the flow of the pump into a surge tank at 0 psi start falling behind, how to I calculate it? I know the volume of fuel it can move is quite a bit higher but I don't want to find out the surge tank is running empty after a long stretch of WOT on a road course.

I may just upgrade it to at least a Walbro to add some safety factor but figured that maybe someone already did the math or tested this at WOT for longer than 10 seconds. I'm thinking it might be ok for pump gas but E85 would throw it over the edge, the thing is I can't really leave it to guesswork either.

AWDTerror

iTrader: (2)

I need some clarification on the 0psi. Wouldn't base pressure be above this?

Well we would really only be concerned with WOT, as that will be the shortest time of available fuel.
How big is the surge tank? And doing some math @ 43psi, the pump would be flowing 3.5 liters per second.

Hiboost

iTrader: (9)

Well the stock pump is only feeding the surge tank and that means it's not fighting to pressurize it beyond 0 PSI unless it is already completely full.

I believe the one MAP sells (actually MPR makes it) is only 1 Liter capacity but you also have the return line filling it with whatever fuel isn't sprayed by the injectors at the rail which is in addition to what the in tank stock fuel pump is constantly sending to the surge tank.

The Fuel Lab fuel pump draws from the bottom of the surge tank and pressurizes the fuel rail to 43 psi base and raises it 1:1 with boost. There is an electronic fuel pressure regulator that actually is demand based so that at idle and low load the return line won't have to flow all 400LPH that the pump can output.

400 LPH would be 6.67 L per minute or .11 L per second assuming no stock pump or return line refilling the surge tank it probably runs dry in just under 10 seconds worst case scenario.

Since I think we will at worst be running 75% fuel pump duty cycle on pump gas (around 550 whp mustang Dyno), that means we will only use 300 LPH which means 100 LPH returns to the surge tank at WOT. So that means .028 L per second is refilling from the return line.

Now take the stock pump at 0 PSI where it's flowing around an estimated 250-275 LPH. That would get the fuel flow into the surge tank with the return line to around 350-375 LPH which is "close" to the capacity of the fuel pump.

If my rough math is correct then 50 LPH or .83 L per minute or .014 L per second is being used out of the Surge Tank worst case scenario on pump gas which is 72 seconds of WOT, I guess I should be good for anything but top speed runs on the salt flats!

Can anyone confirm my math? with E85 using 25-30% more fuel it might still be wise to upgrade the in tank pump though, looks like just a Walbro might do the trick.

AWDTerror

iTrader: (2)

Here is what I found for the stock fuel pump, so your estimate should be correct, worst case scenario is you can just use the 250LPH number, so that way you have an extra margin for error, because I doubt that a pump would flow less @ 0psi than @ 40psi.

This is a 14v mind you.


Your math is correct. What are the LPH specs of the fuel lines? More specifically the return line?

Hiboost

iTrader: (9)

Ah forgot about those graphs that AMS posted, good info.

The feed is -6 AN and the return line is -4 AN since the electronic fuel pressure regulator should keep the pump at low speed for low demand. Worst case we might have to weld in a -6 AN return line to the surge tank and run -6 AN but we should be ok. The overflow from the surge tank to the OEM fuel tank is also -4 AN but the stock nozzle is likely the restriction at -3 AN or there abouts.

AWDTerror

iTrader: (2)

This was the only thing I could find on flow rates for AN sizes.


4GPM = 16LPM which is about .27LPS. for -6AN @ 40PSI.

Hiboost

iTrader: (9)

After talking with Cory we decided to put in a Walbro pump with kit just to be on the safe side. Course now we'll need a fuel filter of some kind, got to love the chain reaction stuff.