V8 conversion fuel line questions (1 Viewer)

[shaggy_mutt]

So the saga of my rebuild and resto continues. When we took the 40 apart, it had a mild 350 and the fuel system consisted of the factory tank setup, with a cracked evap canister and 1/4 (I think?) line to a pretty basic electric fuel pump, then to the Quadrajet.

It now has a more built-up 350 (370hp) with a Holley 4-barrel. Fuel pump is a Carter electric. My question is this: I need more fuel than the 1/4 line will flow, right? Like 5/16? (The carb has a 5/16 inlet, so I assume it doesn't need 3/8 elsewhere in the system) My original plan had just been to run 1/4 line from the tank to the pump, and then 5/16 from the pump onwards, but I'm leaning towards 5/16 the whole way if this is achievable without making massive changes to the tank itself.

So how do I get it out of the factory tank? I searched Mud and found the details of Mr. T's oddball fuel outlet from the tank. Has anyone successfully made a bigger version of that? And is there something I'm missing here?

Guys with big V8's and factory tanks in a pre-75... please chime in! What did you do?

 

[toyotaspeed90]

Couple things to take note of..... most electric carb pumps are pusher pumps.... so they should be within a foot or two of the tank (meaning they aren't good and pulling fuel out of the tank.... they are good at pushing the fuel through the system).

5/16" at a minimum..... though for my mild 350 that's what I used for the return line (being a rochester it has one.... your Holley probably doesn't have a return line)

 

[shaggy_mutt]

Couple things to take note of..... most electric carb pumps are pusher pumps.... so they should be within a foot or two of the tank (meaning they aren't good and pulling fuel out of the tank.... they are good at pushing the fuel through the system).

5/16" at a minimum..... though for my mild 350 that's what I used for the return line (being a rochester it has one.... your Holley probably doesn't have a return line)

Pump location shouldn't be a problem - it's mounted to the firewall (in the engine compartment, not below the dash) below the heater box, so it's pretty close to the tank. Actually, when I was test running it from a gas can, I ran a fuel hose from the pump to a gas can sitting on the ground in front of the truck, and it seemed to work OK.

So if you used 5/16 for your return line, what did you use for the feed line? And how did you attach it to the tank?

 

[toyotaspeed90]

My cruiser was previously set up (built in the 70's I'm guessing) and some things were done right, others not.... they put in a braided 3/8" fuel line that runs to a mechanical pump on the block... so I will be using the same feed line. There was a brass adapter on the side of the stock output line for the feed line.

Just be careful with the pump location..... I've got a carter in my boat that I converted to electric pump and if the fuel line was more than a couple feet long it did 2 things....

1) cheap fuel line was sucked down due to the pressure... I had to use EFI line
2) pressure/volume was low and I could audibly hear the pump struggling. After relocating the pump with a very short line (about 12" long including the pre-pump filter) the same Carter pump had no problems.

Carbs run at a low fuel pressure (usually below 8psi.. which would be considered really high.... FYI the regulator I have on the boat goes from 2-5psi) so you can use simple brass adapters with soft line and normal worm clamps.

 

[shaggy_mutt]

they put in a braided 3/8" fuel line that runs to a mechanical pump on the block... so I will be using the same feed line. There was a brass adapter on the side of the stock output line for the feed line.

So they capped off the original feed line and tee'd the adapter into it somehow? Or... ?

Thanks for the heads-up on pump location btw. I'm using EFI fuel line anyway, just for added protection... had a leak inside the passenger compartment many years ago - that was an eye opener, to say the least!

 

[arndog]

very surprised your carb has a 5/16 inlet on it, I don't think there is any harm in going 3/8s, most cars (muscle cars) of the 60s had 3/8s with a V8 regardless of output and 5/16 with a 6 cylinder

with a holley im sure you can swap out the inlet fitting

arndog

 

[toyotaspeed90]

At least on my 71 - the feed line is on the side of the tank pointing towards the drivers side.... it's sticks out externally about 1/2-3/4" and is threaded. The PO put a brass adapter that the soft line on my rig screws into. They then ran the soft line under the tub, through the frame, and it connects directly to the mechanical pump on the block.

If I were to go electric pump with a carb - I would mount the pump under the seat behind the transmission hump so it was as close to the tank as possible, then run the lines under the tub and through the frame, having it pop out where I need.

 

[shaggy_mutt]

Arndog and toyotaspeed90, the more I think about it, the more I think you're both right. Why try to get away with a smaller size when going to 3/8 is pretty much the same amount of work? I picked up a 3/8 bung and assorted stuff to put a fuel system together - Monday, Lord willing, I'll start putting it all together. Can't wait!

 

[pb4ugo]

GM used 3/8 supply line & 5/16 for the return line on Qjets. I prefer stk mechanical pumps because they used to be very common & still are. You can find them in a rinky dink country parts stores or a pick & pull. I like to use common stk parts that are easliy found in the sticks.

 

[Gumby]

There's a lot to be said for a mechanical pump on a carbed motor.

 

[bikersmurf]

X3 on fuel pump as close as possible to tank. Never had any problem with 5/16 line with 300 hp 350 and carter pump... Even when towing 4000 lb trailer. Never been a drag racer though...

5/16 is huge compared to jet size... Just saying.