FastKat

iTrader: (10)

Will increasing the size of the fuel lines between the pump and the fuel rails increase the amount of HP that a given pump can support? (Assume a return-type system at a fixed pressure...58psi)

For instance, let's say a Walbro 255 can support a max of about 500rwhp through the stock 3/8" lines. Then, you upgrade all of your lines between the pump and the rails from 3/8" to 1/2". Will that pump then be able to support more than 500rwhp? Why or why not?

garage_queen

iTrader: (3)

Might be a good article for you...

http://www.centuryperformance.com/fu...e-spg-140.html

Mattsv8

iTrader: (7)

the thing with them is pressure with more pressure like a efi system you dont need as large a line as a carb system. but im shure there is a point when a -8 feed would be needed in a efi setup. most ive seen with boost run a new feed thats -8 and use the stock feed as the new return line wich is what my plan is with the new turbo setup i plan on droping presure to 43 psi then boost ref on top of that.

FastKat

iTrader: (10)

Thanks for the info guys!

I understand that a larger fuel line may be required to support more HP, but there are a lot of other variable factors that are implied in that statement... like what fuel pump you use. I am asking if increasing only fuel line size will increase the total HP that a given fuel pump can support.

3.4camaro

iTrader: (1)

Simple. Call the manufacturer and ask for the pump performance graph. Then determine the pressure drop created by your fuel lines. This may also be available from the fuel line manufacturer. Make sure you include the pressure drop caused by each bend in the line as well.

Once you have these, you'll know the pump's performance at a given Pressure drop, and you'll have a fuel flow rate, which will give you a hp rating.

FastKat

iTrader: (10)

I appreciate you trying to answer the question, but this entirely misses the point. The goal is not to determine the HP a given pump or system can produce. That has been tested and documented by the real-world experience of board members. I want to determine and discuss what (if any) effect fuel line size has on a give pump's ability to support peak HP. In other words, I want to see if taking a fuel line size from 3/8 to 1/2 will allow a given pump to support more HP.

You do mention pressure drop from each bend, which is relevant. There is also pressure drop on most fittings as well. (A -6 AN fitting does NOT have a 3/8" ID... often times more like 9/32" or so.) I kind of want to keep that aspect out of the analysis, because I think it is adequately covered under the line size.

So-GT0071

I'm still learning fluid mechanics (Have my second class on it next semester) and am not the most knowledgeable guy in the world when it comes to the subject but I'll try to add to the discussion.

I would say that it depends what size your pump has as an outlet. Are we talking about using a fuel line which has a larger inner diameter or a smaller inner diameter than the outlet on the pump its self?

Assuming the pump has an outlet on it with a 1/2 inch inner diameter and your current fuel line inner diameter is something like 3/8 of an inch then it is technically a restriction to the system. The idea is that the system will see a pressure drop when the internal diameter is decreased because it increases the amount of fluid flow head loss or rather the resistance to fluid flow within the system. By increasing the diameter, you would be able to flow the same amount of fluid using the 1/2 inch line as the smaller 3/8 inch line while using less pressure to do so. Differently stated, this would also result in increased overall flow in the 1/2 inch line while using the same amount of pressure that was used on the previous 3/8 line.

Although, the fuel pump will only flow so much because of the internals of the pump, the outlet sizes, and the voltage provided. So while a pump will seem to flow better as the fuel line diameter is increased it is actually just getting closer to what it normally would flow given zero or negligible resistance to flow at the outlet.

I would argue that by changing the inner diameter of the fuel line you are not actually increasing the ability of the pump to flow but rather you are decreasing the resistance of flow the pump is experiencing and therefore getting it closer to its ideal amount of flow.

I hope I'm heading in the right direction for what you are asking.

3.4camaro

iTrader: (1)

It absolutely will allow for extra power, but I can't tell you how much.

You are missing the point, not me. 1/2" line will create a pressure drop just like 3/8" line, just not as much. The larger diameter line will create a smaller pressure drop, but we are all simply bullshitting and pulling numbers out of our asses until someone calls the manufacturer and asks for pressure drop created by a unit length of the line you are using in your system. Then compare to the pressure drop created by the factory tubes, and you'll have an increase in flow rate, which you can convert to hp.

The above poster is correct in saying that the larger line approaches an ideal situation in which there is no pressure drop, and the maximum flow can be delivered, but I'm not going to spoon feed you exact numbers because we can't until you make the call to the manufacturer. This is simple, basic fluid dynamics. Find the pressure drop for each hose, and you'll have your answer.

I agree, the pressure drop created by tubing bends and fittings should be included in your factor of safety, whatever you decide that to be.

FastKat

iTrader: (10)

Which is fine. I'm asking what design would be better, not how much better the new design would be.

This is a much better post - thanks! Sometimes I need less conclusion and more explanation to get things through my head! I figured it would be simple fluid dynamics... which isn't so simple if you've never had any training or experience in it.

FastKat

iTrader: (10)

So here is how I understand it... feel free to comment/correct/etc.

A given fuel pump can support Y amount of flow (gallons per hour - gph) at X pressure (psi). For instance, I attached a copy of a flow vs. pressure chart from the Weldon 600-A. It can support about 62 gph at 58 psi. So, on an LS-based engine requiring 58 psi at the injectors, the HP would be limited to whatever can be supported by 64 gph of fuel. Right? Not necessarily... in fact, probably wrong.

This is where pressure drop comes in... we're talking fuel line size, restrictive fittings, bends, transitions, reducers... anything that the fuel has to flow through until it gets to the injectors creates pressure drop. Let's say that a given stock 3/8" fuel system creates 5 psi of pressure drop when the fuel pump is running the car at peak HP. That means that the pump is going to have to create 58 psi + 5 psi = 63 psi of pressure at the pump to keep the fuel pressure at 58 psi at the injectors. (Assume the regulator is very close to the injectors.) So now you go back to the chart... if the pump has to make 63 psi of pressure at the pump to compensate for the 5 psi lost through the line, then it will only be supplying 60 gph of fuel to the injectors.

So the theoretical verdict is that a less restrictive fuel line will allow a given fuel pump to supply more fuel to the injectors. However, all fuel lines have some restriction, and thus, some pressure drop that must be overcome by the pump. I know that you can eliminate some restriction by using contoured wide bends, using less bends, using less restrictive fittings, and using less transitions. Based on the above posts, you can also eliminate some pressure drop by increasing the size (inside diameter) of the fuel line itself.

3.4camaro

iTrader: (1)

Nailed it.

Now get to work.

Maybe a mod should move this to fueling section.

GNCLONE

I read a LOT about this topic when I installed my sprinkler system.

Your hypothetical larger line increases volume. Volume and pressure are not the same, in fact, they are inversely proportional. This discussion is most germane for one using a carburetor where slight fluctuations in pressure are more critical than in an EFI setup.