I saw this in another forum on this site. It is way above my pay grade.
Does it make sense saying that larger lines don't really help?
Regardless, I think I will at least put 3/8 line in.
Do you need a 3/8" line for that many horsepower? No. Do you need a pump capable of feeding it? yes. I had the Edelbrock pump on my 302 making 375HP, and it feeds it no problem. There are many articles about the capabilities of 5/16" fuel line and how it's been used for most mechanical pumps and engines under 500HP. Many will debate this (especially the people trying to sell you fuel lines!) so do your own research.
The line is the single largest source of pressure drop because it is so long. The 1/4" restriction is very short and the losses are low. The larger the line, the lower the pressure drop at a given flow rate, and the longer the line, the higher the pressure drop at any flow rate. The pump has to suck fuel up the line and once your positive suction head drops sufficiently, you start boiling the fluid in the line and you 'max out' your line capacity. This is even more an issue with impeller (electric) type pumps, but it's true of mechanical ones too.
So first, how much flow do you need for 450HP? Assuming a BSFC of .45 lb/hp/hr, we'll need a minimum of 138lph to supply that. Racers Math 1
Next lets look at line pressure drops @ 138 lph
10 feet of 3/8" line + pressure drop from 3/8" to 1/4": .16 + .03 psi = 0.2 psi
10 feet of 5/16" line + pressure drop from 5/16 to 1/4": .38 + .02 psi = 0.4 psi
So you can see that the line pressure drop is much more significant than the step down to 1/4" at the pump, and that the pressure drop is half in a 3/8" line.
Pressure Drop Online-Calculator
The next thing you have to consider is that when you're accelerating, gasoline is trying to rush back down your line into the tank. Lets say .5G acceleration (120mph trap in 11.3 seconds.) In this case P = rho*g*h = 750 kg/m^3*9.81m/s^2*.5*3m = 1.6psi. This is independent of line size.
I saw this in another forum on this site, that seems to say that large fuel lines are not really necessary? It is way above my pay grade.
Does it make sense?
So the total pressure drop under .5G acceleration for each line:
3/8" line: 0.2 + 1.6 = 1.8 psi
5/16 line: 0.4 + 1.6 = 2.0 psi
Not a big difference. At all.
The vapor pressure of an average summer blend gasoline at 100F is 10.5psi (In Texas. Your state will vary.) Vapor pressure is the pressure at which a fluid starts to boil. So if you are in Texas where the air pressure is 14.7 psi, once you drop the pressure 4.2 psi you start to boil the fluid and you start leaning out. http://www.epa.gov/ttnchie1/ap42/ch07/final/c07s01.pdf Guide on State Summer RVP Standards | Fuels and Fuel Additives | US EPA
You're not close to 4 psi with either the 5/16" or the 3/8" line, so if it saves you trouble and your 5/16" is in good shape, keep it. If it's not, why not upgrade while you're going through the trouble? However, this is only true if everything in the system is 5/16". If your pickup is pinched, your line is pinched, or anything on the tank end is under that, the pressure losses rise quickly, so make sure it is in good shape.