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Fuel Tech Discussion

chucklesas

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Feb 14, 2003
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Dayton, OH
Well, I'm super bored here at work and I've been toying with several ideas in my head and felt like starting a discussion on them. Mind you I don't actually plan on doing any of this, just curious to see what pans out of the discussion.

So, when I was chatting with the CinciDSM group about my proposed setup for my car they were quick to tell me that I'd probably run out of fuel with my single Walbro 255LPH in-tank fuel system. That got me wondering what my best options for fuel delivery would be. I can think of 3:
1. Run 1 really big fuel pump. These seem to be quite expensive >$400.
2. Run another pump in series. Good for high pressure, but still doesn't do much for actual fuel flow.
3. Run 2 pumps in parallel. Good for flow, okay for higher pressure, and could be done on the cheap by doing some slight modification to the stock fuel sending unit, although I'd probably go with a pre-made kit like the Full Blown dual pump setup.

Then that got me thinking... with all this extra fuel how am I going to get it to the rail and back to the fuel tank. What size lines are needed? -6AN(3/8”), -8AN(1/2”). 1 feed line or maybe 2 feed lines to either side of the rail with 1 return line coming out the middle? So then would you run 2 -6 feeds with a -8 return? I tried getting into the equations for internal incompressible viscous flow to determine what pipe size would be needed for a set fuel pressure and flow rate, but there were too many constants that I didn't really have a good number for. I might try to get back into figuring this out later, however my brain has gone into atrophy since college.

What about controlling the voltage to the fuel pump(s) like they supposedly do on the Evos? Then we wouldn't have to worry about upgrading fuel return lines. In the case of running dual pumps we could set the system up so that only one of the pumps is running during idle and low load conditions. I think with Keydiver's chip modifications this is something that could be done while avoiding the standalone ECU. Maybe use one of the EGR, BCS, FPR solenoid feeds to run a relay to control the pumps. What kind of effect with this have on fuel pressure control though? Would we need to run 2 seperate fuel systems and 2 different fuel rails with regulators to properly control the fuel pressure for the varying flow rates?

Of course, there's also the consideration for what type of fuel to run: 93 octane, 110 race fuel, E85...

Anyway, again, I just wanted to get these ideas out there and see where they lead to.
 

Barnes

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Feb 9, 2003
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Richland, WA
I haven't been following your setup, what are you running? E85? Big boost? Big turboozzz? Stroker?
 

chucklesas

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Stroker with a SBR GT-14 turbo (65lbs/min). I plan on running pump gas. I don't actually have the car running yet and have no idea if I'll need to deal with fuel delivery issues. This is more or less just for discussion purposes.
 

belize1334

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Nov 18, 2003
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Bozeman, MT
Two pumps in series will do more for flow than you think provided that the lines are big enough not to be a restriction. With a single pump, whatever pressure you apply at the rail is the load that the pump has to push against. If you run two pumps then they share the pressure load (splitting it between them) just like running two batteries in series in an electrical circuit. So if your manifold pressure is 80psi, the pumps are each only pushing 40psi. If you check the flow tables of a fuel pump you'll see that it flows ALOT more at 40psi than at 80.

I think the bigger issue with running two small pumps in series is that they will each have the total volume flowing through them and the internal size and pump orifice sizes could become a restriction. I could even imagine the first pump cavitating in the fluid bath. That'd be my concern and the reason that I would think two pumps in parallel would be better. Remember, with that huge turbo, you still probably won't actually have boost pressure that's above what other people see...you're just flowing more air at that pressure. Walbros and the like are perfectly happy at 70psi or so just as long as you don't expect them to individually push alot of fuel there. If you run two in parallel I should think that you'd have upwards of 400lph available at 70psi (35psi of boost). 400lph is enough fuel to outflow a set of 1600cc injectors so I think you'd be golden at that point.

Somebody did a writeup a while back about a dual walbro setup using the stock sending unit. They basically replaced the line with higher gauge stuff and then attached both pumps to the hanger so that they both sat down in the tank. You'd need a beefier wiring setup for the current that those things would draw (10amps each can really heat stuff up) but other than that it doesn't seem like to difficult of a setup.
 
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Barnes

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Quoting belize1334:
If you run two pumps then they share the pressure load (splitting it between them) just like running two batteries in series in an electrical circuit. So if your manifold pressure is 80psi, the pumps are each only pushing 40psi.



Are you sure about this? I don't see how it would inherently split the pressure evenly.
 

belize1334

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Nov 18, 2003
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Bozeman, MT
I propose that since the same volume of fuel flows through both pumps, and since there is a one-to-one relationship between a pumps flow rate and the pressure differential across that pump, that they must both provide the same pressure differential if they are identical pumps. This of course is only true of incompressible liquids where the flow rate is the same on both sides of a pressure change.
 
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Charles,
What is your whp goal? 2 in-tank Walbro 255 hp pumps can support 600 whp with as small as a -6 fuel line. I would make sure both pumps are new when you do the install. Jeff can do a chip to turn on the 2nd pump @ higher boost levels.
 

Quoting BarnesMobile:
Quoting belize1334:
If you run two pumps then they share the pressure load (splitting it between them) just like running two batteries in series in an electrical circuit. So if your manifold pressure is 80psi, the pumps are each only pushing 40psi.



Are you sure about this? I don't see how it would inherently split the pressure evenly.



I agree with Belize1334 on this one. The first pump initially puts out 40psi, so the starting point for the second is 40. For it to boost it to 80 only requires it to do is add 40 psi of pressure.

The bigger question is what are your more worried about pressure or flow.
-If your 255 will flow enough at a lower psi, just not at that pressure, then adding a second one in series will do the job.
-If its flow thats your major concern then, series won't do you much good as it'll only increase your flow by ~20% max. In that case dual in parallel would be required, as long as they can both flow enough at that pressure.
-If that still doesn't get you there, then suck it up and buy bigger pumps, or go Bob Norwood crazy and do dual series setups in parallel
 

chucklesas

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Feb 14, 2003
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Location
Dayton, OH
I hate to admit it, but other than getting my car running I haven't really applied any other goals to my setup. I think at this point in time I will be injector/fuel pump limited in my setup.

2.3L block with ARP hardware
8.8:1 compression ratio
FP3 cams
SBR GT-14 turbo (65lbs/min)
PTE/Delphi 1000cc injectors
Walbro 255lph fuel pump (I don't recall if I ended up getting the low pressure or high pressure pump)

Anyway, regardless of my setup I'm just curious to see what types of fuel systems make the most sense for the higher powered guys. I know there's no single recipe for a good setup and that it's based on goals. So for the purposes of discussion I guess we'll say I'm going to try to max out that turbo at around 600HP which probably won't be possible for me anyway since I plan to set my rev limiter at 7500 or 8000 rpm.
 
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The volume requirements for gas are much less than for E85, so you could probably make it work the cheaper way, with 2 pumps in series. For E85 guys making that kind of power I always suggest dual parallel pumps.
Yes, I could also activate a second pump using one of the solenoid outputs. I actually did a test chip for another GVR-4 owner that tested the EVO-type setup with the resistor. I think the results were marginal with the pump he was using though.
 

chvtec33

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May 21, 2009
Messages
29
Location
Tolland, Ct
At the shop I work at we do alot of supercharged and turbo Mustangs and Corvettes and besides the normal 255 upgrade we have two other options before dual pumps or one huge EFI pump.

First is a extra pump inline that supplies more pressure to the rail and it works by not making the 255 struggle to produce the volume at high psi, it only has to feed that booster pump and the booster bumps psi to the rail.

Second option is a voltage booster box which take the 12v going to the pump and raises it to 15-19 volts depending on where it is set at. Granted i know its not good for the pump and life expectancy isnt great for the pump but we see about two years out of Walbro's on this set up and replacing a pump every other year @ $90 or so isn't too bad compared to price of other options.
 
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