Fuel Is It Ok To Run A 3/8" Feed Line And A 1/4" Return?

[ryan7663]

Would there be any problem running a 3/8" feed line and a 1/4" return? I'm replacing the feed line and return line on my 95gt since they were open to the humid gulf coast air for about 6 years. I'm also upgrading to -AN fittings and SS hoses to replace stock nylon hoses. I figure I'll just flush the vapor line out with some Seafoam and blow it out with a air compressor. Instead of staying with the stock 5/16" line diameter I wanted to go to 3/8" so I wouldn't have to get a buch of -6AN-5/16" adaptors. I'm running a Walboro 255lph in case I throw a turbo on at some point. For now though stock power levels, stock injectors, and stock regulator. Thanks for any help or thoughts on this.

I could run a -6AN return line I figure if I need more flow in the return side and just have both the same size. I could then reduce down to -4AN at the tank with a -4AN to -6AN fitting.

 

[jrichker]

Unless you are planning on running pressurized induction or NO2, the stock lines are perfectly good. If you do upsize the lines, the return line needs to be at least as big as the feed line. The reason is if there is restriction in the return line, it increases the fuel pressure. Sometimes an adjustable fuel pressure regulator can adjust it out. Sometimes if the pump is oversized it won't be able to adjust the pressure down to the 37-41 PSI that the injectors are rated for.

 

[ryan7663]

Unless you are planning on running pressurized induction or NO2, the stock lines are perfectly good. If you do upsize the lines, the return line needs to be at least as big as the feed line. The reason is if there is restriction in the return line, it increases the fuel pressure. Sometimes an adjustable fuel pressure regulator can adjust it out. Sometimes if the pump is oversized it won't be able to adjust the pressure down to the 37-41 PSI that the injectors are rated for.

Cool thanks for the help man I'll go with a 3/8" hard line for both feed and return. I'm going to cap off the stock 1/4" line at the pickup and put a -6AN fuel cell bulkhead fitting right next to the hole that the pickup goes in. I should be able to get a crow's foot on it or a L-shaped wrench and tighten it down. I'll probably want to attach the line to the bottom of the bulkhead fitting first so it'll go in easier. I would run my walbro 255lph pump with the stock lines but like I said the old lines are rusted out after sitting open for so long. I can make my own -AN fuel lines for less than what stock replacement lines would run and they don't even make any for my year model(sn95). I would replace them with the same size but they don't make -AN fittings for 5/16" lines except for some low pressure fittings which wouldn't work.

The only thing I'm not sure of now is if I should have the return line only go half way down like the stock pickup or all the way down like this one.http://www.latemodelrestoration.com/Product/Images/GRN-GMTI7998

 

[jrichker]

Copied from the FORD RACING PERFORMANCE PARTS catalog:

PROPERLY SIZING FUEL SYSTEM COMPONENTS

Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”
Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.


My Comments:

A lot of people oversize the fuel pump by buying a 255LPH pump thinking that the fuel pump regulator will just pass the excess gas back to the tank. It does, but… Did you ever consider that circulating the fuel around as a 255 LPH pump does will cause the gas to pickup engine heat? What happens to hot gasoline? It boils off! With most of the 5.0 Mustangs having the carbon canister removed or disabled, the car stinks like gas, and the gas mileage drops since the hot fuel evaporates away into the air.

 

[ryan7663]

Thanks for the info I didn't consider the heat build up part. I've actually replaced every part of my emission system including putting in a brand new charcoal canister I ordered from rockauto.com. Do you think this would be a big enough problem that I should shelve my 255 for another day and get a walbro 110 or 155?

My old lines are rusted period I can't reuse them so I have to make new ones since nobody makes stock replacement sn95 lines. Plus I already have all the -AN fittings and 50ft of zinc-plated 3/8" tubing to do this. Would I have any problems with psi running the 110 or 155lph pumps through the 3/8" lines? Thanks again jrichker you've been a big help.

 

[jrichker]

I would use a 155 LPH pump along with the 3/8" tubing you are planning on using. Note to check the flare angle on the AN fittings. Real AN fittings are 37 degree angle flares while automotive and household flares are 45 degree angle. The flaring tools are not interchangeable, and the 37 degree flaring tools are expensive. Check with the fitting supplier, they may have the AN style fittings available with a 45 degree flare angle. Then you can use an ACE Hardware or home improvement supply store 45 degree flaring tool for 1/2 the cost of a 37 degree flaring tool.

I recommend that you use some 3M Weld-Thru Coating II sprayed on the lines to cover the nicks and scrapes that are a part of fabrication. It will prevent the lines from rusting where the zinc coating has rubbed or scraped off.
See http://www.tcpglobal.com/spraypaintdepot/weld-through-primers.aspx. Your local auto body supply may have a similar product.

AN fittings require a 37 degree flaring tool. A standard automotive or household plumbing tool is 45 degrees and cannot be used with AN flare fittings. If you do, the flare is subjected to too much stress when the fitting is tightened, and is likely to fail or leak.

See http://www.mscdirect.com/ , http://www.mcmaster.com/ or for the flaring tool you will need . Prices start at $85 and go up

http://www1.mscdirect.com/CGI/N2DRVSH?PACACHE=000000013509163

View attachment 145168

http://www.mcmaster.com/#flaring-tools/=b4fxc3

Last time I was in Summit racing, they had a 37 degree flaring tool for less than $40. It may or may not be a catalog item.

For some help fabricating your own stainless steel hose assemblies, see http://www.turbinefun.com/Stainless_Braided_Hose_Assembly.asp

For stainless steel braided hose and fittings for automotive use:

See http://www.summitracing.com/search/?keyword=stainless steel hose&dds=1
http://www.summitracing.com/search/?keyword=stainless steel hose&dds=1

http://www.jegs.com/webapp/wcs/stor...hall&searchTerm=stainless+steel+hose&x=18&y=4

See http://www.eaton.com/Eaton/Product...rformanceProducts/FittingsProducts/index.htm for more information on High performance automotive hose products

 

[ryan7663]

Cool I can get the 155 $20 cheaper than the 110 so I'll order the Walbro 155 next payday thanks again man. Thanks for the tips and yeah I know about the 37 degree flare I bought a new Ridgid 377 ratcheting flare tool a while back. I didn't know they made -AN fittings in 45 degrees sizes but it's cool I have the right tool to do the 37 degree flares but thanks for the advice. I haven't heard of that 3M Weld-Thru coating I'll order some as I had planned on coating the lines with something but wasn't sure what was best. I'm going to do my best to match the bends on the old lines as to minimize the work under the car.

Not a really big problem but where do you think the best place to end the return is? The way I have it planned now is to put a bulkhead fitting right next to the hole for the pickup. Then I'm going to have a drop tube go down off of that and have it end at or maybe a little below the level that the stock one did. I figure I should maybe put a angle fitting on it and direct the return flow at the pump to cool it down like the stock setup did? Do you think that's a good idea or should I just have it drop down to the general area of the pump? Thanks again

 

[jrichker]

It seems that the stock location dumps the return fuel right down on top of the fuel pump. That way it serves to cool the pump and keep it running consistently. If the pump is hot, the dump of fuel flashes into vapor and cools the pump down. Pour rubbing alcohol on your hands on a warm day and you'll get the same cooling effect.

 

[ryan7663]

That's what I thought I 'll make sure I have the new return pointing at the pump thanks again man for answering my many questions I got it all figured out now. Just checked my order status at summit and my lines will be here tomorrow so I'll get to work on it this weekend.