fuel system design

[blkZooM]

As Motown stated I'm not too sure the Walbro 400 will play nice with returnless style, believe it just flows too much. Are your target numbers at the crank or rwhp? Forgive me read this years ago so I can be wrong I remember reading as you increase boost the fuel pump basically starts to battle the base fuel pressure and what ever boost you are seeing example 39.9 plus 21 psi so the pump is now working against 61 psi at the rails I don't know what the numbers are for the 340 or Walbro 400 at 60 psi but that's what you would need to see then plug in the numbers to see if it could support your target numbers. Small lines are just going to make an already uphill battle awfully harder for the single alone. I overbuilt my system from the go I had e85 in mine when I was planning it so I know it will do well on pump -8 an hose twin 340 lph pumps, twin racer x modified fpdm wire upgrade fuel rails (I was force to purchase bigger ones) and the 55 lbs injectors I showed you. Only thing needed in the future is bigger injectors and a dual bap.


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[lifespeed]

Some assumptions are 0.6 Brake Specific Fuel Consumption (reasonable for an efficient blower, might want to use 0.65 for roots, 0.55 for turbo, 0.5 for NA, etc). This is crank horsepower of course, even if you lose it in the drivetrain you still have to burn the fuel.

Fuel pump math:

(700HP * 0.6 BSFC) / (1.585 lbs/L) = 265 L/hr

Units:
BSFC = lbs/(hp*hr)
gas weighs 6 lbs/gal * 0.26417 gal/L = 1.585 lbs/L

The thing to watch out for is fuel flow vs pressure. With 15 psi in the manifold The fuel pump will need to supply 55 psi at the injectors, plus frictional losses in the plumbing. Could easily be 60 to 65 psi required at the pump.

So read the flow vs pressure graph. This one is a comparison from Radium Engineering. One might want to get the plot from the manufacturer to be sure.


To convert to PSI multiply Bar pressure by 14.5

[lifespeed]

As Motown stated I'm not too sure the Walbro 400 will play nice with returnless style, believe it just flows too much. Are your target numbers at the crank or rwhp? Forgive me read this years ago so I can be wrong I remember reading as you increase boost the fuel pump basically starts to battle the base fuel pressure and what ever boost you are seeing example 39.9 plus 21 psi so the pump is now working against 61 psi at the rails I don't know what the numbers are for the 340 or Walbro 400 at 60 psi but that's what you would need to see then plug in the numbers to see if it could support your target numbers. Small lines are just going to make an already uphill battle awfully harder for the single alone. I overbuilt my system from the go I had e85 in mine when I was planning it so I know it will do well on pump -8 an hose twin 340 lph pumps, twin racer x modified fpdm wire upgrade fuel rails (I was force to purchase bigger ones) and the 55 lbs injectors I showed you. Only thing needed in the future is bigger injectors and a dual bap.

It is possible the stock lines won't be adequate. I am looking for 600 HP at the wheels, and yes the flow is needed at 40 psi + manifold pressure.

As for the Walbro 400 being "too much" for returnless, theory says it doesn't work that way. The pump is controllable and can operate to very low levels by the PCM. Of course that is theory, and I know some people have had issues. But others have been successful. I think a turbine-style pump properly controlled can be operated over a very wide range of flow and pressure. If it doesn't work and I am wrong I'll let you know.

[blkZooM]

Well hopefully it works out for you, I I've only read that it doesn't work. I've never really looked into them because they can only take 14 volt and I plan on using KB daul BAP 17v down the road.


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[lifespeed]

Well hopefully it works out for you, I I've only read that it doesn't work. I've never really looked into them because they can only take 14 volt and I plan on using KB daul BAP 17v down the road.

The Walbro 400 flows enough at 12V for my requirements. Another complication eliminated (KB BAP).

[blkZooM]

I plan on running e85 and I don't think the two 340 lph would be enough for what I want to run. I don't even think two Walbro 400 is enough and with the uncertainty if they'll even work with the returnless, I will need about 30% more fuel for e85 and a bap is the easiest way at least with the returnless I think


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[lifespeed]

I plan on running e85 and I don't think the two 340 lph would be enough for what I want to run. I don't even think two Walbro 400 is enough and with the uncertainty if they'll even work with the returnless, I will need about 30% more fuel for e85 and a bap is the easiest way at least with the returnless I think

Multiply a gasoline supercharged BSFC of 0.6 to 0.65 by 1.3 and calculate it out for E85. There is no extra credit for providing much more fuel than needed.

With a return system the FPDM control loop is different, I don't know how this is implemented. Obviously the PCM is no longer controlling fuel pressure, but how this is addressed in tuning I don't know.

While the KB boost-a-pump does work and has its uses, it is another component that may not be necessary for some fuel system designs. The one thing that concerns me (in a returnless design) is how gracefully does the PCM fuel pressure control respond when the "gain" of the fuel pump suddenly increases when the BAP switches on at 3 psi.

[blkZooM]

I can't answer your first question. But I believe most splice the two wires together and keep the bap on all the time, so you don't have to worry about waiting for 3 psi it's always ready to go


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[lifespeed]

I plan on running e85 and I don't think the two 340 lph would be enough for what I want to run. I don't even think two Walbro 400 is enough and with the uncertainty if they'll even work with the returnless, I will need about 30% more fuel for e85 and a bap is the easiest way at least with the returnless I think

How much horsepower (at the crank) do you want to provide fuel for?

[Turbov6Bryan]

I'll probably go with the Walbro just to be sure. My current plan is to use the stock hard lines, rails and a 3" filter. If anything else besides the wire gauge and FPDM needs upgrading I'll do it as needed.

Ok
So we're done with this thread then.

One heck of a try for an engineers approach to "design" a fuel system for a marauder.... What a disappointment to your future self

Just messing with you man, don't hate me because your "design" is pretty much what any person would do... Drop in a larger LPH or GPM pump

I was expecting http://www.watermanracing.com/Pages/fuelpump4.html
A actual fuel pump design worthy of the title for this thread

Just busting your chops

[lifespeed]

Ok
So we're done with this thread then.

One heck of a try for an engineers approach to "design" a fuel system for a marauder.... What a disappointment to your future self

Or I could just guess . . .

[blkZooM]

How much horsepower (at the crank) do you want to provide fuel for?

Can't answer that at the moment, my end (mind you I'm in the beginning) goal is to simply go all in with a 2.3 TVS off of a 13/14 GT500 Bigger TB, port etc and max it out on e85.


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[lifespeed]

Anybody know the stock fuel line inside diameter? Fuel pump wire gauge? Eyeballing it looks like 10G.