how much hp will 3/8 fuel line handle?

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i think most 9-11 second car owners on this board must own stock in magnafuel, as they all seem to run their 1200-1500 dollar setups on cars that in no way need them( na)

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yea but they look purty

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bigger will NEVER kill your engine like a lean
condition will

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Going lean in the lights can cost you more than most fuel systems.

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Going lean in the lights can cost you more than most fuel systems.

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i have 3/8 at 650 hp, with a carter mechanical race pump. my pressure gauge hardly drops at all during a run, so i couldn't tell you how close i am to the limit w/my combo. put a fuel pressure gauge in it. then you know.

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The only true test is watching the gauge throughout a run. If it will hold the same PSI start to finish, you are good to go.
On fuel line size , so many variables come in to play, it is very difficult to put a hp number to any particular fuel line size.
Length of the line, number of bends, G force, pump pressure
and any variance in voltage will change the rate of flow. So the real answer is "it depends".
The end result needs to be will there be enough fuel delivery to keep the bowls at the same level at all times. That is a lot easier with four needle and seats on a tunnelram/dual four combo. A high hp dominater is one of the toughest to feed. Only two needle and seats, and often lots of hp.

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...Too big of a fuel line can be a problem if the cell and pump are in the back of the car and the car leaves extremely hard...

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One of my Mopar manuals has a line about fuel line diameter and acceleration and it's totally wrong. I'm pretty sure they deleted it from later manuals. To reiterate: the pressure generated from accelerating a column of fluid is independent of the area of the column (or in this case, the diameter of the fuel line). The pressure generated is the product of the fluid density, acceleration rate, and the height/length of the fluid parallel to the direction of acceleration. Cross sectional area doesn't figure in at all. For instance, the pressure 50' below the surface of Lake Superior is the same as the pressure 50' below the surface of lake Huron, even though one has a much larger area. Let's put this myth out of its misery.

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doesn't the inertia from the weight of the entire fuel column come into play? Essentially if you think of the fuel in the fuel line as solid, the force generated back to the pump cavity (and thus the pump vane/motor) would be it's mass times horizonal acceleration. The larger the mass (Diameter), the more force is put on the pump vane to keep it all moving forward.

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What do you think?

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Let's put this myth out of its misery.

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Where the diameter of the fuel line comes into play is the velocity of the fluid within the line. Head losses or pressure losses are related to velocity squared divided by 2 x force of gravity times the head loss coefficient of the tubing. So essentially a larger diameter tubing reduces the fuel velocity and the pressure losses.

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The mass/inertia of the fluid does come into play, that's why the density is in the the equation. Area doesn't factor in at all.

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So essentially a larger diameter tubing reduces the fuel velocity and the pressure losses.

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In firefighting Pump operations this is referred to as friction loss. The larger the hose diameter the less friction loss given the same hose length and discharge pressure.

Good discussion

My old 446 was using a 3/8 line with a Carter HV 120gph mechanical. The car ran 116mph @ 4100 raceweight...do the math.

The new 572 will be using 8an lines with a Mallory 250 and return style regulator. This motor made 705hp on Dwayne's dyno.



Ron

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The larger the hose diameter the less friction loss given the same hose length and discharge pressure.

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B U T ....a fire-hose is that traveling from a dead-stop to 60 mph in 2 seconds or so !

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3/8 "is the outside diameter. The inside is @1/4"

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the inside is 5/16" on a 3/8" steel line

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Ok, lets do some math...

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Take the 3/8" diameter
So 3.1415 x .375"^2 x 100"x .0267lbs/in^3= 1.17 lbs mass

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1. Area = pi*D^2/4, your volume calculations are 4X too big. 2. You're using solid mechanics math on a fluid mechanics problem.

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There are two separate issues and some are confusing them. One is the acceleration of a fluid and I've explained that one previously, the size of the line isn't an issue. The other is the pressure loss from fluid flow through the lines and fittings. This is the area people should focus on. First find your actual max. flow rate and then calculate the velocity in the line and determine if you need a bigger line. See this page: http://en.wikipedia.org/wiki/Reynolds_number

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I have one stock 5/16 fuel line feeding both carbs. [Email]10.35@134.4[/Email] and 770HP on the dyno..

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Thats all I need know! Thanks Dave!

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There are a lot of possible explanations for all this but one is a car that falls on its face at 900-1000 feet due to fuel starvation.

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it's a FAST car...quite literally

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Can anyone on here verify if the fluid dynamics theory are based on stationary commercial applications? I'm thinking, that if that is so, then they, it, does not apply to fluid systems mounted onto accelerating vehicle like race cars, race boats, airplanes and rocket ships

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I've had a few tell me I may not have enough fuel for my car. My 74 cuda with 440 has 530ish Hp. I run a holley black pump with a regulator at carb which is an 850. no return. I doesnt stumble nor seem to fall on its face so i havent paid much thaught to it. My 1/4 mph is usually between 117-118mph.

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Looks like you are good to go. The most important consideration is line size from the tank/cell to the pump

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I have one stock 5/16 fuel line feeding both carbs. [Email]10.35@134.4[/Email] and 770HP on the dyno..

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I just don't see why you think the mass of the fuel can be ignored.

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This fluid dynamics thing is not that easy to understand < at least not to me> you guys are saying that the dia of the line does not make a difference psi, so a 1" pipe that is 100ft tall will take the same energy to lift as a 2" pipe 100ft tall, but what about the amount < volume> of liquid coming out the end? If ya read all the fuel pump guys versions for the need of a larger fuel system it kinda makes sense, can some one link together both pressure and volume as related to a racing fuel system? As is, it seems to me that a small pump with a large hose should work for the most part, so why are we buying large pumps? I started out with 2 Holley reds with 2 3/8 fuel lines feeding a 850 dp Holley and just about every one busted my chops about it

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EMarine, the concept is hard to grasp I admit!

I too was skeptical, it went against what I felt was common logic. But fluid dynamics have thier own logic ways of working.

In your example the 2" diameter 100" column of fuel would have more mass. But the PSI pressure at the bottom would remain the same for both diameter pipes. The difference in mass of the 2 columns wont make a difference.

As a Example, take a 100 gallon Fish tank that has alot of water mass. Run a 1/4" diameter hose connected from the bottom of that tank up the side of it to the top.

Fill that 100 gallon Fish tank with alot of water mass and see what happens to the Low mass 1/4" column hose.

Will the Large Mass volume of the 100 gallon tank force water to gush out of the low mass 1/4: tube??

No, It will self level itself to the tanks water level. Why is that when you have that 100 Gallon mass? Fluid Dynamics!


To answer your question about Volume. The Pump works against pressure not mass. With both pipes having the same PSI but different Diameters.

Once fuel starts moving, line friction comes into play. The Faster the fuel moves, the more line friction and the more pressure is created in the line. Smaller lines if to small for the pump will create more resistance to any pumps rated flow vs a bigger line.

The bigger lines extra fuel mass will have no effect on the pumps abilty to flow its rated Volume. To small a line or too many turns and orifices will. mike





EDIT!!! Id Like to thank Jamesc, RobbMC and Firefighter Ron For Schooling me on this in the past!

Cokebottle kid I dont think discussions like this are ever Pointless.

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I just don't see why you think the mass of the fuel can be ignored.

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As a Example, take a 100 gallon Fish tank that has alot of water mass. Run a 1/4" diameter hose connected from the bottom of that tank up the side of it to the top.

Fill that 100 gallon Fish tank with alot of water mass and see what happens to the Low mass 1/4" column hose.

Will the Large Mass volume of the 100 gallon tank force water to gush out of the low mass 1/4: tube??

No, It will self level itself to the tanks water level. Why is that when you have that 100 Gallon mass? Fluid Dynamics!

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To answer your question about Volume. The Pump works against pressure not mass. With both pipes having the same PSI but different Diameters.

Once fuel starts moving, line friction comes into play. The Faster the fuel moves, the more line friction and the more pressure is created in the line. Smaller lines if to small for the pump will create more resistance to any pumps rated flow vs a bigger line.

The bigger lines extra fuel mass will have no effect on the pumps abilty to flow its rated Volume. To small a line or too many turns and orifices will. mike

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