Fuel line size

[E5 Charger]

Replacing my complete fuel system on a 74 with a small block. Not sure what I'm building yet, but should be in the 300-400 HP range. 5/16 and 3/8 fuel lines are the same price. Should I upgrade to 3/8? Any issues going to the larger line? Or is the stock size 5/16 fine for this HP range?

[E5 Charger]

I should have mentioned that I'm keeping the stock look, so will use a mechanical fuel pump.

[303 Mopar]

Either would work, but as long as you need to buy new lines I would upgrade and install a return line while you're at it.

[green69rt]

Since nobody chimed in, I will start.  My old Charger with a 440 had a 3/8 line and made an advertised 375.  I would guess that a 5/16 line would be fine, most of the time, but right at the edge of being able to flow the max amount of gasoline when you are at top HP.  Especially with a regular mechanical pump, since you will be sucking on the line it would push you closer to vapor bubbles forming in the line (especially on a hot day.)  You'd be pushing the envelop, so to speak.  Just put the 3/8 line in and    forget about it.

[E5 Charger]

The 74 already has a return line, so good there. I was just wondering if the larger 3/8 main line would cause less pressure with a mechanical pump. Kind of like when you pinch a garden hose and the water comes out faster. I guess there isn't much difference in size between 5/16 and 3/8.

[A383Wing]

I'm running a 383 with dual four barrels on my Charger, still running the stock 5/16" fuel line, still running a stock mechanical fuel pump....no problems with any fuel issues at all since installation back in the late 70's

Bryan

[E5 Charger]

From what I have read, it looks like most cars came with 5/16 except for hemi and 440 6pack. I guess i'm more interested to know if the 3/8 could be too large. The price of the two are the same, so that's not the issue. I just don't want to use the 3/8 because that's what everyone is doing and find out it's too large for my application.

[birdsandbees]

Well if you go 3/8".. next thing you'll need a 3/8" tank outlet or be adapting the connection hose on the existing from 5/16 up to the 3/8 line.

[E5 Charger]

I'm replacing the whole system, so will need a new tank and sending unit. It looks like the sending units are the same price for either size. Just wondering if there are issues with the larger line, especially if I only reach 300 HP in my future build.

[440]

If it's the same price upgrade to 3/8 as it gives you more headroom to play with later if you so desire.

For what it's worth my 350 chev went to 7k rpm on a mechanical pump and 5/16 line before it ran out of either air or fuel.

[BSB67]

Won't hurt, won't help.