Dual Walbro Pumps - AFR dropping like a rock

[chicago TDP]

OKAY, I am having an issue with my car right now at WOT.
The set-up is as follows:
1969 Nova
2007 4.8L STOCK
6.0L truck heads with valves n springs
160 # FIC's
Two in tank walbros (second comes on at 8 psi)
T70 (have a TC76 on the shelf for it)
T56 6 Speed
Boost Ref Reg @ 38 # 1:1

The car runs great on the street, afr with no boost is always around 14.7.
When I run the car up to about 5#'s, 11.5 AFR
As soon as hit the Hobbs switch and turn on the second pump, my WB freaks out which I think is due to dropping below 7.4.
Sometimes, I can back out of it and the gauge with pause but then get back in the game and read out again at the correct amount, i.e 14's.

Now, what I think is happening is when I hit the hobbs and the second pump comes on, in the scanner I have seen 9.0 recorded in the AFR histograms from my LC1 WB.
At this point, I am a little weary to try and tune WOT with the pump kicking on at that boost pressure.
I can drop the activation point lower and maybe make the tuning easier but I am afraid that pulling the fuel out VIA the VE table is going to make the table ugly.

Any suggestions?

Also, the car is on 93 gas now.
The injectors are so large because I am going to shoot for running E85 and 1000 RWHP later this year or next year.
Running premium is a stepping stone at this point but I would like to always be able to run 93 if I need.

Any help would be great!

Adam

[smithers]

Sounds like a mechanical issue, not a tune issue.
Regulator unable to 'regulate' (e.g. either not large enough, not large enough return)
What is your rail pressure doing when the 2nd pump is activated?
Just sounds like your 38psi pressure is going considerably up when the 2nd pump activates causing your rich condition.

[mecanicman]

X2
What regulator/size return line are you running. I am running the same setup and went for the big magnafuel with -8 return.

[chicago TDP]

I have the BIG magnafuel Boost Ref FPR.
The feed line is -8 and the return is -6.

I do not know my line pressure at this time when the second pump kicks on...my autometer gauge stopped working for some dumb reason which I need to figure out this week cause it is annoying not being able to check the fuel pressure in the scanner...

MECANICMAN, you have a second walbro as well???

[mecanicman]

yes

[chicago TDP]

yes

At what boost pressure do you have your pump kicking in?
Did you see your AFR drop when the pump came on?

[mecanicman]

I have not started wot tuning yet, still putting finishing touches on. I have my hobbes switch at 2 psi. I had it idleing with pressure gauge on it and jumped second pump on because I was afraid of exactly what you are describing. At idle I picked up about 3psi. I think you need to upgrade to to -8 return. Did you buy the magnafuel orb fittings? They claim to increase flow thru the regulator over standard an fittings.

[Rinkrat456]

A slight off-topic question...since you both have dual walbro pumps, what made you decide to go that route? Is it horsepower level, boost level, simply because of a turbo? I'm curious to know if a single walbro 255 is enough to support a 6.0L on 7-8psi of boost because that's what I'm planning. Already have the W255, I just figured 255 liters was enough to supply the power levels.

[mecanicman]

When I bought my setup some of the other options available now were not out yet. Walbro goes in tank, reasonably quiet, and performes well. A single would probably have kept up with my goals, but as pressure goes up flow goes down. Wanted a safety net, and the added advantage of if one pump fails somewhere, I can jump the second a still drive home.

[chicago TDP]

I have not started wot tuning yet, still putting finishing touches on. I have my hobbes switch at 2 psi. I had it idleing with pressure gauge on it and jumped second pump on because I was afraid of exactly what you are describing. At idle I picked up about 3psi. I think you need to upgrade to to -8 return. Did you buy the magnafuel orb fittings? They claim to increase flow thru the regulator over standard an fittings.

Well, I was thinking of just dropping the HOBBS down to 2-3 PSI so that I would have better "control" of tuning with both pumps on.

I do have the ORB fittings on the FPR.

There are a bunch of guys over on the LS1 tech forum that run the -8/-6 and have no issues so that is what I went to for the time being.
I think I will be upgrading this winter to all teflon lines so that the E85 does not destroy all the braided line.

[chicago TDP]

A slight off-topic question...since you both have dual walbro pumps, what made you decide to go that route? Is it horsepower level, boost level, simply because of a turbo? I'm curious to know if a single walbro 255 is enough to support a 6.0L on 7-8psi of boost because that's what I'm planning. Already have the W255, I just figured 255 liters was enough to supply the power levels.

I was told to not trust a single walbro past 500 HP so I put in two.
I know at this point that the combo that I have built should be 650 RWHP.
Right now, I am hitting 125 MPH in a 1/4 mile and I am not shifting fast or taking the engine over 6000 PRM.

Also, I am running super rich so with "leaner is meaner" type thinking, I know that when I tune the WOT, the car is really going to move out and need fuel.

The last thing you want is not having enough fuel to supply your engine.

[robbyredneck]

just so were all on the same page. what is your flow path. pumps>feed>rails>regulator>return?

[killerjuice]

Your -6 an return line is plenty. I run a FORE triple Walbro 255HP intank setup, -10an feed and a -6an return. I can run as low as 43psi with all 3 pumps running. I used to have a 1:1 into boost and a 43.5psi static FP, but after talking with some tuners and my map looking a little funny I opted to run a static FP of 58psi. I run 2 pumps all the time, and have the 3rd as a reserve for c-16.

I would run both pumps all the time and forget about it, it is something so simple and has no negative side effects. plus it rules something out. post a screen shot of your VE table, you might need a slight dip coming into boost, my table has needed it.

-Garrett

[chicago TDP]

just so were all on the same page. what is your flow path. pumps>feed>rails>regulator>return?

You are correct on the way my system is set up.

[chicago TDP]

Your -6 an return line is plenty. I run a FORE triple Walbro 255HP intank setup, -10an feed and a -6an return. I can run as low as 43psi with all 3 pumps running. I used to have a 1:1 into boost and a 43.5psi static FP, but after talking with some tuners and my map looking a little funny I opted to run a static FP of 58psi. I run 2 pumps all the time, and have the 3rd as a reserve for c-16.

I would run both pumps all the time and forget about it, it is something so simple and has no negative side effects. plus it rules something out. post a screen shot of your VE table, you might need a slight dip coming into boost, my table has needed it.

-Garrett

Okay, I thought the -6 was alright.

I think I am going to kick the second pump on at 1 psi of boost.
That way, It is there at the start of BE/PE and it will be simpler to tune.
Seeing as I drive the car 90% on the street (almost every day now) I do not want to run two pumps and re-circulate that fuel that much.