Walbro 400 install and pump pressure/flow testing
 

I finally got around to installing a Walbro 400 that David Buschur gave me (Thanks!). Its being held in with a hose clamp rather than the fuel pump cap. It takes very little clamping force to hold it in very tightly. Since it doesn't have the cap, its also lacking the bowl for the fuel siphon return. Based on other people's experiences with fuel pressure overrun at idle, I drilled out the siphon hole to 3/32" (2.4 mm). Best as I can tell, 3/32" is barely larger than stock, and from watching my fuel pressure at idle after installing the pump, my guess is that drilling it probably was not necessary to maintain fuel pressure at idle (and during cruise when the fuel pump is in low voltage mode).

Anyhow, after a bit of fiddling around with the install, I fired up my Evo. Net fuel pressure at idle was 44 psi which is what it should be. (Quick clarification: Net fuel pressure is fuel rail pressure minus boost and should always be 44 psi for a stock fuel pressure regulator.) The crossover load for full voltage mode was tuned for my Walbro 255, and as I suspected, net fuel pressure jumped to 60+ psi (should always be 44 psi) when the ECU kicked the higher flowing Walbro 400 over to full voltage, and pressure didn't drift back down to 45 psi until the fuel demand had increased by a fair amount. With my Walbro 255, it would bump up to about 46 psi net fuel pressure for just a split second and then settle back down to 44 psi. I ran out of time to fiddle around today, so tomorrow I'll be raising the crossover voltage to try to get rid of the pressure bump...

Well, I couldn't increase the crossover load nearly as much as I anticipated. Fuel pressure fell off drastically in low voltage mode for anything more than about 4 psi of boost. Final values for the crossover load are only about 5-15 load higher than what I used for my Walbro 255. Fuel pressure bumps up only slightly at the transition to full voltage.

Another suprising result is that even with this pump, net fuel pressure is still falling off somewhat at WOT high rpm with my current power of ~485 who on E85. By 7500 rpm and 27 psi of boost, my Walbro 255 falls off to about 36 psi net pressure, while the Walbro 400 is falling off to 40 psi net pressure (should be holding 44 psi all the time). This is with the fuel system in top condition - upgraded fuel pump wiring, new fuel pump carrier (i.e., new internal filter), new Walbro 400 fuel sock, new OEM grommet on the fuel pump outlet, and using a Wilson monster diameter fuel rail. Nothing much left to upgrade. With fuel pressure so similar to my Walbro 255, I'm wondering if there is a significant flow-induced pressure drop in the factory fuel line as fuel travels from the pump to the rail, and as a result, the pump seeing something like 20 psi higher fuel pressure than at the rail. I'm starting to think that replacing the stock hardline with -6AN isn't such a bad idea.

With that said, the extra 4 psi of fuel pressure from switching to the Walbro 400 did richen up the AFR by half a point. I suspect I'll pick up a few more psi of fuel pressure when I lean the AFR back out by 0.5 pt (or slightly more).

Leaning out to 12.0:1 allowed the fuel pump to hold 43 psi out the top, so its basically right at the envelope of sustaining 44 psi. I'm still puzzled why a Walbro 400 can't easily hold the pressure, so I ordered everything I need to make fuel pressure measurement at the fuel pump outlet. This weekend, I'll be doing voltage and pressure measurements at the pump.

Why didn't you chose to go with the aero motive 340 instead?

CBRD lent me one to try. Flow rate and pressure holding capacity were horrible compared to a Walbro 255 or DW300. Not sure why it was like that. Perhaps it was a defective unit.

https://www.evolutionm.net/forums/ve...mp-wiring.html

please keep posting results!

cb

I just purchased a aero motive 340 to replace my 255 thinking its a significant improvement. Looks like that was a dumb move

Holy crap finally! I've had mine in since January with good results.

This is a good pump to get the most out of a BBK on e85! 255 and the others fall a bit short.

Are you still on the stock fuel rail? I had great luck swapping in an aftermarket unit on my X, made all the difference! Veeerrrry curious to see how re-running the line does for you....I *think* I will be able to get by w/o doing that on my car...still on stock FPR.

Other thing you can try is lowering base fuel pressure...I did it by elongating the stock FPR body (inadvertently, see my build thread)...but an AFPR would be worth trying if you're needing to get a bit more out of the pump.

Did your Aeromotive unit have the polarity reverse from stock or Like stock?

Only reason i ask, i built a double pumper off two 340's. The first set i got was reverse polarity, they actually didnt work too well. Sent them back and they sent me a set that had the stock polarity....and run great, for the last 6 months.

cant wait to see the results.

I was under the assumption that the new walbro was only minimally higher flow then the tried and true 255 at stock voltage, but run them 16-20 volts and they really start to shine, kind of like a big turbo at low boost..

I've had a Wilson fuel rail for the last year or more. It has 11/16" ID, one of the biggest on the market. Depending on the fuel pressure results, I may get an AFPR. I have a pretty strong feeling that a -6 AN fuel feed line will make a huge difference and may actually force me to get an AFPR to prevent overrun.

I didn't pay attention to whether it had reverse polarity. Interesting to know.

FYI

From Aeromotive FAQ page:

11.) Q: I heard the 340 Stealth Pump may have reverse-polarity compared to the pump I have in my car now. What does this mean, what should I do about it, and if the fuel pump is accidently wired wrong, could it be damaged?

A: The original version of the 340 Stealth Pump, which began shipping in February 2011, had a positive/negative (+/-) orientation on the pump that was later found to be opposite factory orientation in some of the more popular applications. A change was made to the +/- position of the pins on the pump and the included pig-tail, in the fall of 2011, correcting this issue. At the same time additional updates were performed to the inlet end caps of the 11141 and 11142 pumps in order to better fit and secure the inlet filter/sock. In order to help distinguish the new version, and for enhanced cosmetic appeal, at that time the inlet end cap color was changed from white to red, so all current Stealth pumps feature inlet and outlet end caps molded in red.

In all cases, the original and the current version 340 Stealth pumps have had the correct markings for +/- (correct wiring polarity) molded into the pump’s outlet end cap, just below the pins in the plug. Simply confirming that the wire connected to the terminal marked with the + sign is the 12V hot lead from the car’s harness is all that is necessary to ensure proper electrical polarity of the motor. This is true for any 340 Stealth Pump, regardless of version.

So what if the pump was accidentally wired backwards? Since the 340 Stealth Pump employs a DC 12 Volt motor, reverse wiring is not immediately damaging to the motor, however the pump will run in the wrong (backward) direction, resulting in no positive flow or fuel pressure. Continued running of the fuel pump in this manner will eventually damage the pumping mechanism and motor shaft bushings due to lack of lubrication and cooling flow. If your fuel pump runs when power upt, but does not make flow and/or pressure, be sure to check the polarity of the wiring before running the pump repeatedly, or for extended periods of time.

http://aeromotiveinc.com/tech-help/f...th-fuel-pumps/

Thanks. The one I tried had a red cap (and it flowed fuel), so that eliminates it as being an older model with reversed polarity at the terminals.

So is the 400 a better pump than the 340 or we havent gotten to that conclusion yet

I was right about the pressure drop in the stock fuel line. I measured a whopping 16 psi pressure difference between the pump housing outlet and the fuel rail at WOT 7800 rpm just before I let off. Its probably 1-2 psi worse at the pump outlet itself.

First set of pics below show the adapter I made up log fuel pressure. It just barely all fits in there. I had to tweak the 45 deg connector to get everything to line up. I would have loved to log outlet pressure using a pressure sensor, but it wasn't worth the cost of another sensor. I checked the accuracy of the gauge by starting the car, letting it warm up and then killing the motor. Fuel pressure holds high because the check valve in the pump outlet prevents pressure release. The gauge pressure matched the rail pressure of 43 psi pretty much exactly.

I ended up using my camera to make a video of the gauge during my WOT run. Worked like a charm and got good pressure data. The data plot shows pump outlet pressure sitting approximately 14 psi higher than fuel rail pressure for most of the run, and then as the motor revved out past 7500 rpm, the pressure difference increased to 16 psi with the pump housing outlet sitting at 84 psi just before I lifted. Fuel pressure directly at the pump outlet is probably 1-2 psi higher. During the run, I observed fuel pump voltage to be about 13 volts, so using the Walbro 400 data chart, I get an estimate pump flow rate of 250 lph at 85 psi and 13 volts. The FIC1100 injectors are at about 90% IDC (E85), so 90% * 4 injectors * 1.1 lpm *60 minutes = 237 lph. It all adds up pretty well, and basically what's happening at WOT is that my injectors are consuming all the available fuel that the pump can send with virtually none going down the return line. No eff'in wonder I can't maintain any margin of fuel pressure at the rail.

So there ya go. I think the bottom line is that anyone making more than 450 whp ought to considering running larger diameter fuel line from the pump housing to the rail. -6 AN is what most people run, and it should reduce the pressure drop to less than 5 psi at 500 whp of E85 fuel flow. Its either that or run a boost-a-pump, but that will likely drive pump outlet pressure up to 90+ psi where the pump flow begins to fall like a rock.

One other comment I'll make is that running -6 AN line will likely allow a Walbro 255 or DW300 to support significantly more power. My guess is that anyone who has been able to make more than 500 whp on either of these pumps with E85 was running upgraded fuel lines or a boost-a-pump. Either that or their fuel pressure was falling off without them knowing it.


Adapter assembly to allow monitoring fuel pump outlet housing using stock fuel feed lines. The adapter that attaches to the pump housing is Russell PN 644120 (I had previously incorrectly listed it as 670340). Its sweet. They also make one with a -8 AN outlet.
https://www.evolutionm.net/forums/at...hmentid=187191


Here's the installed adapter assembly. It just barely fit.
https://www.evolutionm.net/forums/at...hmentid=187192


Video of the gauge during the WOT run. I double-stick taped my point-and-shoot camera to the back of the console. Kinda cracks me up.
http://youtu.be/6oueiLW-5P0


Here's the data plot. Currently making at least 485 whp DJ. Might be closer to 500 whp.
https://www.evolutionm.net/forums/at...hmentid=187194


Here is the Walbro 400 flow data. Pump was at 13 V and 84 psi at liftoff. Interpolating between 85-90 psi and 12-13.5 volts, I get about 250 lph of flow which is just barely enough for 500 whp.
https://www.evolutionm.net/forums/at...hmentid=187195

Dude, this is AWESOME info and testing. Thanks for taking the time to do it and share your conclusions.

BTW, I maxed out Buscher's double pumper system (through the stock fuel lines) at about 760whp on a Mustang dyno on E-85.

I just switched everything over to a -8 feed and -6 return along with two new Walbro 400 s on the double-pumper. Will be shooting for 850-900 in a few weeks.

It certainly was an eye-opening experiment. My feeling at this point is that a fuel supply line upgrade can do more for fuel supply than a fuel pump rewire, and its not that hard to do.

I'll bet that pump pressure was 95-ish psi when you were running double-pumpers on the stock fuel line. Net fuel injector pressure was probably falling to about 20-35 psi depending on your boost level. You'll have massive amounts of flow with your new setup, probably 3x the flow capacity.

<mistake>

he's using E85, not normal pump fuel.

Awesome testing results, it's always a great feeling to prove yourself right with solid data. Well done {thumbup}

The male end all the way to the left that will allow the stock line to clip onto, have the P# for that? I need that{thumbup}

Russell PN 640940.

I've now got Earl's -6 AN braided stainless teflon hose installed from the pump to the rail. What a PITA... took me most of the day to get it installed reasonably cleanly. Below is a pic of the fittings I used to mate the hose to the fuel pump outlet. Total cost of fittings and hose was around $120. The hose is super tough and impervious to any fuel, but its super stiff. If I were to do it again, I'd be tempted to use Earl's high-end hose with the ultra flexible teflon and kevlar braid. Its 4x the cost though. At any rate, the -6 AN hose had virtually no flow restriction, and pressure at the pump outlet was only ~3 psi higher than pressure at the fuel rail. That's a 12-13 psi pressure reduction which is good for about another 50 lph of fuel. Net injector pressure now looks to be holding 44 psi across pretty much up to max fuel requirements.


Fittings at the fuel pump outlet
https://www.evolutionm.net/forums/at...hmentid=187812


Log showing only ~3 psi difference between pump outlet pressure and fuel rail pressure
https://www.evolutionm.net/forums/at...hmentid=187813

excellent! im glad more and more people are doing things the smart/correct way instead of tuning around pressure drop. there is zero downside to larger fuel lines. any added volume between the pump and regulator can only do good.

btw, russell also makes the same fitting in a direct push on model.

http://www.summitracing.com/parts/RUS-640853/

With the 400 pump we were able to make about 510 whp on E-85 with the stock wiring. Once we added a rewire kit the car was able to make 586. This happen on both Evo's and DSM's for us.


-Em

Yeah, I've seen that one. I think the one I'm using is a little more compact which is helpful for the tight space.

Factory fuel supply line?

mfred, in post #16 you're listing the adapter that attaches to the pump housing as a Russell PN 670340.

But when I check on the Summit Racing website, it shows a Russell Fuel Pressure Take-Off :

http://www.summitracing.com/parts/RUS-670340/

Would be great if you could list the part number of the adapter to the pump housing in -6AN and or -8 AN.

Thanks for your help and testing!

Oops. Correct PN for the quick connect that attaches to the pump carrier outlet is (3/8"): blue = 644120, and black = 644123

Also, if anyone wants to connect to the metal hardline, that is a different size (5/16"): blue = 644110, and black = 644113

Any updates on this?

I've been running the -6 AN hose + Walbro 400 for a few weeks now. Everything is working fine. The only thing new is that I've decided that my FIC1100s are going static as the motor crosses about 6500 rpm. Time to get bigger injectors.

Things I'm considering trying are:

1) Combine the factory fuel hardline under the car with custom connections at the pump and at the fuel rail. There are three sharp 90 degree fittings in the factory connection between the pump and the hardline, so I'm curious how much pressure loss these and the short sections of flexline are causing.

2) I think I'm going to build a doublepumper using my Walbro 255 and DW300 pumps. I've been trying to figure out a clean set of fittings for the pump housing outlets.

I have one of the E85 versions on the way and am sure i will need to upgrade my line to get what i need out of the pump,, i would rather not add anymore aftermarket stuff though.

They are available now?

Mine will be here tommorow yes.

Would- p/n 644123/644110 also work for the return to pump housing??

No modification is needed for the return line (or siphon line) to the pump housing (aka carrier).

i have a full -6an return line in the car, it was previously a fullblown setup. was having some issues and making a dp now, if i dont have to do the -6 bulkhead on the return i'd be happy to get away with it.

The factory return inlet is a barbed fitting, so the push-on EFI fittings won't work. If you're not running some sort of custom bulkhead into the fuel tank, then a transition from -AN to hose is probably your best bet. Another option might be a transition to a teflon Swagelok fitting. A teflon Swagelok fitting would be pretty bullet-proof.

Walbro 400 was very easy to install into sending unit.. thanks to the forums..

yeah my plan was 2 -6an bulkhead fittings for the feeds, and the -6an fitting for the return. all 3 bottomside would have a -6an to 5/16th barb fitting. But if there was an efi fitting that would work for the return that'd be better than having to do that third. Have all the parts and if my current issue isnt solved thats my weekend project.