When should I have my second fuel pump kick on?

[The Granny]

Here are my mods: stock crank, stock rods (shot peened and polished), 30 over trw forged Pistons, 218/212 comp hyd. roller cam, t&d 1.55 roller rockers, well ported iron heads, rjc fmic, single m15 nozzle alky, pte 3 bolt .85 ar 6870 turbo, 120lb injectors, stock intake/tb, ta race headers, 3" downpipe with a dump under the passenger seat floorboard.

Haven't tested the car at all yet, I'll be getting it back this evening from a chassis shop and I'd like to take it out for a few pulls tonight and turbo the boost up past 5psi.

I've got two walbro 255lph external fuel pumps.

Any ideas on when I should have the second pump turn on? I'll be using rpm/boost (I believe aux out 2?) to activate the second pump.

 

[TurboDave]

I turn mine on at 15 # of boost.


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[The Granny]

I turn mine on at 15 # of boost.


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Is your set up similar to mine? sorry I'm on my phone and can't see signatures if you have a list of what you've done in there.


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[TurboDave]

Mine is a very mild setup that only runs mid 11's. I don't run alky. The second pump is a safety margin.


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[TurboDave]

When I was racing I run 27 psi of boost on race gas.


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[The Granny]

When I was racing I run 27 psi of boost on race gas.


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Gotcha, a single 255 and meth should support me to around 15psi smoothly. I think I'll start there once I take my car out to test it. In the mean time, I'll keep searching on here and see what else I can find, I appreciate your input!

 

[Reggie West]

You list alky in your sig. Ifyou are using it you may need it using those HUGE injectors. Normally you would not need it with alky in the picture.

The turbo will be supported in terms of fuel requirements with alky and pump gas. You have enough pump to run E85 all by itself.
Food for thought.

 

[The Granny]

You list alky in your sig. Ifyou are using it you may need it using those HUGE injectors. Normally you would not need it with alky in the picture.

The turbo will be supported in terms of fuel requirements with alky and pump gas. You have enough pump to run E85 all by itself.
Food for thought.

Unfortunately the pumps I have aren't compatible with E85 http://walbrofuelpumps.com/walbro-gsl392-inline-fuel-255lph-pump.html

I'm a little confused by your first sentence.. are you saying with my injectors, a single 255 pump, and alky I may not[I/] need the second pump at all?

FWIW I'm on the fence about getting another nozzle.. haven't tested the car on a single nozzle so I'm not sure if it needs it. My goals are to run mid 9's with this combo

 

[Reggie West]

You can run 9.90 all day with a single nozzle set up. After that you would need to upgrade to the second nozzle.

I'm a little confused by your first sentence.. are you saying with my injectors, a single 255 pump, and alky I may not[I/] need the second pump at all?

Yes that is exactly what I'm saying.

Unfortunately the pumps I have aren't compatible with E85 http://walbrofuelpumps.com/walbro-gsl392-inline-fuel-255lph-pump.html

I'm a little confused by your first sentence.. are you saying with my injectors, a single 255 pump, and alky I may not[I/] need the second pump at all?

FWIW I'm on the fence about getting another nozzle.. haven't tested the car on a single nozzle so I'm not sure if it needs it. My goals are to run mid 9's with this combo

 

[The Granny]

You can run 9.90 all day with a single nozzle set up. After that you would need to upgrade to the second nozzle.

I'm a little confused by your first sentence.. are you saying with my injectors, a single 255 pump, and alky I may not[I/] need the second pump at all?

Yes that is exactly what I'm saying.

Interesting.. I'll have to research signs of when a fuel pump is maxed out, that way I can be as cautious as possible and recognize the signs if they ever do show up. I was under the impression this 255 lph was undersized for a car with 9 sec potential.

If this is the case I better get a second nozzle, I'd rather be safe than sorry


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[Mr.Spool]

Here are my mods: stock crank, stock rods (shot peened and polished), 30 over trw forged Pistons, 218/212 comp hyd. roller cam, t&d 1.55 roller rockers, well ported iron heads, rjc fmic, single m15 nozzle alky, pte 3 bolt .85 ar 6870 turbo, 120lb injectors, stock intake/tb, ta race headers, 3" downpipe with a dump under the passenger seat floorboard.

Haven't tested the car at all yet, I'll be getting it back this evening from a chassis shop and I'd like to take it out for a few pulls tonight and turbo the boost up past 5psi.

I've got two walbro 255lph external fuel pumps.

Any ideas on when I should have the second pump turn on? I'll be using rpm/boost (I believe aux out 2?) to activate the second pump.

You need to be looking at the Afr to really know.but it's safe to say you need to turn it on in advance of higher rpm/boost ex below 20psi.keep the timing low till you get a handle on it with a rich Afr.Twin pumps big injector and a single nozzle can make 9sec power but I do like the twin nozzle for that kind of power.

 

[The Granny]

You need to be looking at the Afr to really know.but it's safe to say you need to turn it on in advance of higher rpm/boost ex below 20psi.keep the timing low till you get a handle on it with a rich Afr.Twin pumps big injector and a single nozzle can make 9sec power but I do like the twin nozzle for that kind of power.

so I guess it'll start to lean out heavily at a certain boost and that'll be when I need the pump to come on? I agree that I'll need to turn it on in advance that way I know it'll be on before I need it. I'll go in my tune and check but if I remember right I believe Cal set the timing very conservatively. I'm looking into a second nozzle right now


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[Chuck Leeper]

Per Julio, on the application on my LS: AIRC, when/if I get to 900FW, switch to 2 15 nozzles.
Currently 1 -10, 1 -15. No intercooler, so I'll start out w/ the current combo. May use some C110, should I venture to the track. No sense in trying to use hi boost on the street.
Doesn't Walbro publish flow/pressure curves? I don't see a single 255 in a heavy car, going 9's w/o a lot of alky as a crutch.
As suggested: Sneak up on it!
In addition to watching the AFR, the DC, I'd be looking REAL close at the plugs.

Back under my inj bench...

 

[ttypewhite]

The second pump should come on at 15psi. Be careful how far you push that turbo with stock crank and rods. That is definitely the weak link in your set up. Just ensure that your tune is spot on.

 

[The Granny]

Per Julio, on the application on my LS: AIRC, when/if I get to 900FW, switch to 2 15 nozzles.
Currently 1 -10, 1 -15. No intercooler, so I'll start out w/ the current combo. May use some C110, should I venture to the track. No sense in trying to use hi boost on the street.
Doesn't Walbro publish flow/pressure curves? I don't see a single 255 in a heavy car, going 9's w/o a lot of alky as a crutch.
As suggested: Sneak up on it!
In addition to watching the AFR, the DC, I'd be looking REAL close at the plugs.

Back under my inj bench...

Yes they've got their flow chart online here
My battery shows around 13.5v on a light pull so I'll look at that line to see what kind of flow I can get. base fuel psi is 45, so 20psi boost brings it to 65psi of fuel. it'll flow ~59GPH at that level. Using Tyler's there here, hp x bsfc (750 x .7) (using .7 because I'll be spraying meth so it'll raise it from it's typical .6-.65?) I get a demand for 87.5 GPH of fuel. So the single 255 won't support this. I'm not sure it'll take me 750 to crack the 9's either, but even if I lower it to say 650 I get a demand of 76 GPH from my pump. Maybe my calculations are off, but if they're not then one 255 pump is severely undersized.

Picking 15 psi of boost and 60 psi of fuel, the pump will flow ~61 GPH. If 15 psi of boost makes 500, using the same method as before I'll need 59 GPH of fuel so I'm safe there. Maybe I should set it to activate around 13 psi?

Chuck, what will happen to the DC? Will it begin to rise exponentially as I approach the limits of one pump?

 

[The Granny]

The second pump should come on at 15psi. Be careful how far you push that turbo with stock crank and rods. That is definitely the weak link in your set up. Just ensure that your tune is spot on.

I agree.. pulling the motor and sending it off to the machine shop was one of the first things I did with my car about a year and a half ago, and I didn't do enough research beforehand. I wish I did, had I done that there's no way I would've put the stock crank and rods back in. But, I'm stuck with them for now and will see how it goes. I've got a base tune from Cal, but I also plan on having him remote tune my car hopefully soon, especially since I know I'm playing with fire with the stock crank/rods

 

[Jerryl]

IMO:

There is NO straight answer on when to turn on the pump on your car, with your fuel and your tune, at your boost level.
The decision should be guided by data, and should not be a guessing game.

 

[Jerryl]

Btw:
Since you are on XFI . . .
You should look into using the FP correction (FPC) feature. Turn the pump on early, log, study the data and adjust from there.
The FPC is an exceptional feature and works extremely well.

I am sure everyone (well, most?) will agree:
Never use alky as a fuel supply as a crutch. On a 13 aecond car it may work. On a 10 second car, it's a dangerous strategy.

 

[ttypewhite]

IMO:

There is NO straight answer on when to turn on the pump on your car, with your fuel and your tune, at your boost level.
The decision should be guided by data, and should not be a guessing game.

Not sure I agree with that (no disrespect intended). But I don't think at 15psi his car will crank over 600hp to cause any issues where fuel is concerned. The 2nd pump isn't feeding it's own line to the front, it's adding volume to a line that is already full. I would tune around the 15psi activation point and adjust my map accordingly.

 

[Jerryl]

Not sure I agree with that (no disrespect intended). But I don't think at 15psi his car will crank over 600hp to cause any issues where fuel is concerned. The 2nd pump isn't feeding it's own line to the front, it's adding volume to a line that is already full. I would tune around the 15psi activation point and adjust my map accordingly.

True. Adjusting around the VE map is one way to accmplish it on XFI.
I would rather change one setting and get it close than chase a bunch of VE cells.

If he had a chip car as 90% of the cars . . . That wouldn't be as simple.

With that thought process of VE table adjustments . . . . would it not make sense to turn it on at 8psi, in case he decides to go e85?

Also . . .
If the XFI FPC is turned on . . . It shouldn't matter much correct?

I have much respect for your accomplishmenrs, and am certainty NO EXPERT. Always learning . . . . .