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

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.

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.

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

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.