Actually, it's the friction losses in the feed line that create artificially high pressures at the pump head at the worst possible point in the curve - around peak hp. That means to get an indicated 75 psi at the rail, the pump is working against 85-90 psi, which reduces volumetric capacity as any pump flow chart illustrates.

The second part of the problem is because unless the car can be operated at WOT in high gear with someone carefully watching a fuel pressure gauge all the way through the run, this problem usually goes unnoticed. The reduced pressure across the injectors is a one-way ticket to destruction. There are forum members experiencing this problem right now, but they're unaware of it.

The factory return creates issues at low speeds, the factory feed creates issues at high speed, high power. Everyone talks about the former because it's easy to see. They aren't talking about the latter so much because it isn't easy to see. Most that do have pressure gauges have rail-mounted gauges, and they've not taken steps to check it at high load, high power. When not on the dyno, this can be done by connecting an external fuel gauge and line to the rail, and running the tubing and gauge up to the windshield so it can be monitored. It isn't pretty, but it works, and it saved my rear end at least once.

 

Let's say you get all those problems well taken care of (the FPR, lines, return, everything good) and now you just want to calculate how much of a fuel pump you need to support a certain hp level. Can you get a pretty accurate picture for that by using the Deatsch Werks calculators?
I'm thinking for example on an AWD 4g63 car:
700 awhp .... if drive train loss is about 15%, then crank hp is about 823.
put 823 into the top line of their Fuel Injector Calculator http://www.deatschwerks.com/resource...tor-calculator
fill the rest of the blanks, turbo, e85, 100% duty cycle = 1404cc/min injectors required.

Then in their Fuel Pump Calculator
http://www.deatschwerks.com/resource...ump-calculator
Fill in the blanks: 4, 1404, 43.5, 30, Return, Calculate = 337 LPH fuel pump capability required at 73.5 psi


This would be a bare minimum because I put 100% duty cycle in the injector calculator, which you wouldn't want, but for getting the minimum fuel pump size, would this be pretty realistic? These numbers I picked BTW are just about smack-on with what a Walbro chart shows for the 450, at ~75psi and 13.5 volts.

 

The calculated minimum pump size is realistic for your calculations, but it is a minimum. These calculators are based upon well-trodden physics, and provide good guidelines for the minimum of what would be needed. When it comes to pump, injectors, and fuel lines, one should size everything for more than those minimums by a reasonable margin (e.g. 25%), particularly where the pump is concerned.

 

Right, cool, understood, and thanks!

If I were to try to estimate how many liters per hour flow I could get from 2 Walbro 255hp pumps in series with each other (1 in-tank going to 1 inline) at some fuel rail pressure XXpsi, using the Walbro charts, and well-trodden physics – how would I do that? I’m kind of interested in the comparison of a pump setup like that, versus a single Walbro 450, or versus anything for that matter.

 

In that case, you would save yourself the trouble of making estimations and look at the magenta line on the chart attached here. Keep in mind that this data is reported at 14V, which means heavy gauge power and ground wiring to each pump is required to reproduce these figures.

 

I doubt even with good wiring the pump sees 14v. I routinely see my system voltage drop to 13 on data logs at WOT..

 

I have two 255s running full time, with 4 AWG power and ground wiring, and pump voltage never drops below 14V at WOT. This is why I am frequently emphasizing the importance of power and ground wiring that supports the full demand of these pumps.

 

I've never measured power at the pump, I was just referencing system voltage in my logs. But I don't see how the pump would get more power than the ECU.


My walbro 450 is wired to the battery which is 3ft away in the trunk with a 30 amp relay and 10g wire supplied in the STM kit, and a 10g ground. This wiring is activated when the stock system goes to high voltage, and it supplements the stock wiring. The pump runs only on the stock wiring when the system is in low voltage mode.

 

This chart is excellent, so thanks, I had not found this before.

Interesting to me in 2 ways:

1.) The red line they show for 2 255’s in series does what I thought it would. They show about 288 lph at 75 psi. I was estimating about 270 lph at 75 psi just using the Walbro charts and basic physics, at 13.5 volts. Pretty close! And of course the flow is less if you go to higher pressures. So I get that red line.

2.) They also show “Walbro 255 lph hp in-tank to external 255 lph hp parallel” with the light blue line. What the heck is that? I mean, diagram wise, what are they doing there? How do you have an in-tank and an external in parallel? That system, whatever it is, sounds like what I might want!

 

Checking power at the pump is the only way to know what's happening at the pump. The same is true for any component. Do not assume the ECU voltage data to be reflective of anything aside from voltage at that particular point in the ECU. Check the voltage at your alternator with engine running at reasonable speed (e.g. 2000 rpm) as a reference, realizing that less voltage at any point elsewhere in the system reflects a voltage drop. Where this is difficult to do, checking the voltage at the battery terminals with engine running at 2k as a secondary option. That is your reference point.


I don't know exactly what AMS did for its test rig, but it may have involved an aftermarket, external fuel cell with a sump for external pump. Dedicated race cars often use these.

 

Yeah, I looked around a little bit for somebody using this on a street setup and it wasn't exactly jumping out at me. I put an email question in to AMS to explain it to me, not expecting much on that, will probably call them at some point to ask about it. Seems to me like any way of adapting it to a stock fuel tank setup would have the problem where the external pump would start up dry every time it switches in, or else you would have to run it continuously which would delete one of the reasons for having it in the first place.

Just thought I would mention this factoid: Book value for resistance of 10 gauge wire is 0.9989 ohms per 1000 feet. So 3 feet of 10 ga wire would have a resistance of .003 ohms.
V= IR
V=20 x .003 (where 20 is a high guess at your current to the pump, in amps)
= .06 volts voltage drop in your 3 foot run of wire - not much! Times 2 if you have another 3 foot run of 10 ga ground wire. Still not much at .12 volts, but it would have a little effect.
http://www.powerstream.com/Wire_Size.htm

I like the dual voltage thing. Do you know what the lower voltage is, about?

 

Whatever factory is. I think its in the 10 volt range. But only the factory wiring supplies the pump with power in low voltage mode. When the stock system kicks into high voltage, both the stock wiring AND the "rewire" I did supply the pump with full voltage.


If the car ever gets a full fuel system upgrade, I will probably redo it to simply be acitivated by a hobbs switch. Its a bit complicated the way it is now. I don't even remember how it's done without looking at the diagram I made for it, but I had to use two relays for it to function properly.

 

If you do ever fix the fuel system problems you mentioned earlier, I would be interested in knowing what your injector duty cycles are at max. Currently I imagine they are higher than they should be because of the issues. I am going with the FIC high-Z 1650's also, which is why.

I see in your sig "English Racing tuned - Mustang dyno 452whp". Do you have any thoughts on how the Mustang numbers compare with numbers from the ER dynojet?

Did ER have any comments pro or con about the Walbro 450?

 

Here's my experience with the W450:

https://www.evolutionm.net/forums/ev...w-testing.html

This thread includes drag pressure measurements for the factory supply line and -6 AN line for a ~500 whp Evo on E85.

The OP of this thread was probably splitting the grommet for several reasons. My guess is that it could be a combination of all four of the following: 1) Possibly had stuffed the grommet over the W450 barbs which are huge. 2) Possibly had hardwired the pump for full time full voltage. 3) Possibly had not drilled the siphon. 4) Possibly using a crappy aftermarket grommet.

Bottom line is that the W450 needs the following to work properly:

1) Drilled out siphon.
2) Two stage power supply.

For anything more than ~480 whp on E85, the factory supply line should be swapped for at least -6 AN to reduce drag losses. My feeling is that the factory return line is adequate as long as Items #1 and #2 are implemented properly.

 

My punched 255 is simply running out of flow. I have not rewired or drilled anything. Is this something I should entertain before purchasing a walbro 450?

I had hoped I could leave everything as is other than dropping in the 450 and POSSIBLY replacing the FPR.

Does anyone have a clean how to for rewiring the fuel pump to retain dual voltage operation? I keep hearing hard wired this and that makes me visualize huge wires sliced right into a battery.