Barracuda Challenger Forum

Author Topic: 5/16 to 3/8 fuel line  (Read 464 times)

Offline DadsCuda

  • Jr. Member
  • **
  • Posts: 73
5/16 to 3/8 fuel line
« on: June 21, 2017 - 09:14:24 am »
After all my research & doing the best I could to get the proper specs on this 67 notchback Barracuda, I struggled to figure out the size of the fuel lines. I settled on 3/8, as that's what my research seemed to point to. Again, I'm not knowledgeable enough to just eyeball something like that. I boutght new sending unit, tank, filter, clips, and now the pre-bent line. Getting ready to put it all together, I can see the old line is a 5/16.
Can I simply swap it all out to 3/8 if all the new stuff is the same size? Do I need (should I get) a new fuel pump to match a bigger size line?
Any advice here is appreciated. I'd rather not unbend the line if I'm gonna have to send it back.
Thanks




Offline burdar

  • Sr. Resident
  • ******
  • Posts: 5924
Re: 5/16 to 3/8 fuel line
« Reply #1 on: June 21, 2017 - 09:56:22 am »
3/8 line is a common upgrade.  There are different sending units for 5/16 and 3/8.  As long as you have a sending unit with a 3/8 nipple you are good to go.  Most stock style fuel pumps will only have a 5/16 inlet.  I think you will be fine.  If you wanted to look for another pump that has a larger inlet, you could do that.  I believe 5/16 line is good to around 500hp so I don't think you HAVE to upgrade. 

If your 67 is anything like my 68 Dart, the fuel line and brake line use the same style clips.  They should work on both 5/16 and 3/8 I would think.

Offline DadsCuda

  • Jr. Member
  • **
  • Posts: 73
Re: 5/16 to 3/8 fuel line
« Reply #2 on: June 21, 2017 - 11:09:33 am »
That's such a relief! The clips are just different enough that the 3/8 line doesn't snap in, which was the real indicator that I may have a different size. But I have the correct clips, too.


Online cudabob496

  • Sr. Resident
  • ******
  • Posts: 6721
Re: 5/16 to 3/8 fuel line
« Reply #3 on: June 21, 2017 - 01:56:13 pm »
no use getting 3/8, if there is a 5/16 restriction anywhere in the system
72 Cuda, owned 25 years. 496, with ported Stage VI heads, .625 in solid roller, 254/258 at .050, 3500 stall, 3.91 rear. 850 Holley DP, Reverse manual valve body.
Up to 4000 RPM, Warp Speed, Up to 5000, Rediculous Speed, Up to 6000 RPM, Ludicrous Speed!

1999 Trans Am, LS1, heads, cam, headers, stall, etc! Love to surprise the rice rockets with this one. They seem so confident, then it's "what the heck just happened?"

Offline DadsCuda

  • Jr. Member
  • **
  • Posts: 73
Re: 5/16 to 3/8 fuel line
« Reply #4 on: June 21, 2017 - 02:41:53 pm »
no use getting 3/8, if there is a 5/16 restriction anywhere in the system
Could you explain what you mean by 'restriction'? would a 5/16 restriction just be a 5/16 size line anywhere in the system? or would it be pertaining to the carb? I mean...am i good as long as the entire system is switched over to 3/8...main line, carb to pump, sending unit, vapor line, lines to filter...does the pump pose an issue, if i don't replace the original?

Online cudabob496

  • Sr. Resident
  • ******
  • Posts: 6721
Re: 5/16 to 3/8 fuel line
« Reply #5 on: June 21, 2017 - 04:20:36 pm »
Could you explain what you mean by 'restriction'? would a 5/16 restriction just be a 5/16 size line anywhere in the system? or would it be pertaining to the carb? I mean...am i good as long as the entire system is switched over to 3/8...main line, carb to pump, sending unit, vapor line, lines to filter...does the pump pose an issue, if i don't replace the original?

anywhere in the line.  Some folks have 3/8 fuel line, but then a 5/16 pickup in the gas tank.
In that case, might as well have 5/16 line from the tank to the carb.
72 Cuda, owned 25 years. 496, with ported Stage VI heads, .625 in solid roller, 254/258 at .050, 3500 stall, 3.91 rear. 850 Holley DP, Reverse manual valve body.
Up to 4000 RPM, Warp Speed, Up to 5000, Rediculous Speed, Up to 6000 RPM, Ludicrous Speed!

1999 Trans Am, LS1, heads, cam, headers, stall, etc! Love to surprise the rice rockets with this one. They seem so confident, then it's "what the heck just happened?"

Offline DadsCuda

  • Jr. Member
  • **
  • Posts: 73
Re: 5/16 to 3/8 fuel line
« Reply #6 on: June 21, 2017 - 06:41:03 pm »
anywhere in the line.  Some folks have 3/8 fuel line, but then a 5/16 pickup in the gas tank.
In that case, might as well have 5/16 line from the tank to the carb.
But as long as the main line & sending unit are the same....?
My concern then is the carb to pump lines I ordered didn't actually specify size (ordered based on car & engine) but they appear to be 5/16. Which is good bc it fits I the carb (& so presumably the fuel pump), but will that discrepancy cause trouble? Do I need to find new lines pump to carb...and further, will I have figment issues with the bigger lines connecting to the old carb ?
Sorry to ask so many questions but I have no idea... 😟 :clueless:

Offline Cudakiller70

  • Sr. Member
  • ****
  • Posts: 1720
Re: 5/16 to 3/8 fuel line
« Reply #7 on: June 21, 2017 - 10:26:16 pm »
I think your OK.
You have a 3/8 fuel tank sending unit and a 3/8 main fuel line. That'll work.
That gets you to the fuel pump.
The only thing we need to figure out is how you are going to connect the 3/8 main line to the fuel pump.

Does your fuel pump have a 5/16 fuel inlet made for a 5/16 hose connection or is it 3/8"?

Are you good/connected from the fuel pump outlet to the carb inlet?
« Last Edit: June 21, 2017 - 10:31:04 pm by Cudakiller70 »
Auto spell I'm tired of your shirt
The above is just my opinion
Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other.
John Adams

Offline jimynick

  • Resident
  • *****
  • Posts: 3823
Re: 5/16 to 3/8 fuel line
« Reply #8 on: June 21, 2017 - 10:59:54 pm »
There's a Weatherhead adapter to go from 5/16ths to 3/8 that'll screw into the pump and attach to the line. Unless it's a race car, don't sweat the necking down. It's better to have the latent capacity of the 3/8ths than not.  :cheers:

Offline Cudakiller70

  • Sr. Member
  • ****
  • Posts: 1720
Re: 5/16 to 3/8 fuel line
« Reply #9 on: June 21, 2017 - 11:05:51 pm »
I think the pump has a 5/16 hose barb inlet connection that isn't changeable  :dunno: don't really know yet. If that's the case would just suggest this fitting to adapt it.
http://www.jegs.com/i/JEGS-Performance-Products/555/15946/10002/-1
« Last Edit: June 21, 2017 - 11:17:16 pm by Cudakiller70 »
Auto spell I'm tired of your shirt
The above is just my opinion
Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other.
John Adams

Online cudabob496

  • Sr. Resident
  • ******
  • Posts: 6721
Re: 5/16 to 3/8 fuel line
« Reply #10 on: June 21, 2017 - 11:19:52 pm »
lotta fuel pumps neck down to 5/16 somewhere.
Gotta be careful.
72 Cuda, owned 25 years. 496, with ported Stage VI heads, .625 in solid roller, 254/258 at .050, 3500 stall, 3.91 rear. 850 Holley DP, Reverse manual valve body.
Up to 4000 RPM, Warp Speed, Up to 5000, Rediculous Speed, Up to 6000 RPM, Ludicrous Speed!

1999 Trans Am, LS1, heads, cam, headers, stall, etc! Love to surprise the rice rockets with this one. They seem so confident, then it's "what the heck just happened?"

Offline DadsCuda

  • Jr. Member
  • **
  • Posts: 73
Re: 5/16 to 3/8 fuel line
« Reply #11 on: June 22, 2017 - 04:38:22 pm »
so the way the lines were set up before, the main line did not actually connect to the fuel pump, line to line...it was main line-rubber hose-fuel pump. then hard lines from pump to carb (5/16 size). it looks as if my  brother added fancy braided lines which actually look bigger than the hard lines coming from the pump, but it could be an illusion.
and at the rear (tank) i think it was also line-rubber hose-sending unit...
so i'm down to the decision of getting the proper lines from pump to carb.... the new pump to carb lines i ordered did not specify size, but they are pretty clearly 5/16. it seems as though, from this line of advice and insight, that my best option is to get new pump to carb lines to match the 3/8 main line.
and there's no way to use the 5/16 pump to carb lines along with 3/8 main line...
is that correct?

Online cudabob496

  • Sr. Resident
  • ******
  • Posts: 6721
Re: 5/16 to 3/8 fuel line
« Reply #12 on: June 22, 2017 - 05:45:13 pm »
for simplicity I have rubber fuel lines going into and out of fuel pump.
Might have to shield them from heat, though.
72 Cuda, owned 25 years. 496, with ported Stage VI heads, .625 in solid roller, 254/258 at .050, 3500 stall, 3.91 rear. 850 Holley DP, Reverse manual valve body.
Up to 4000 RPM, Warp Speed, Up to 5000, Rediculous Speed, Up to 6000 RPM, Ludicrous Speed!

1999 Trans Am, LS1, heads, cam, headers, stall, etc! Love to surprise the rice rockets with this one. They seem so confident, then it's "what the heck just happened?"

Offline Cudakiller70

  • Sr. Member
  • ****
  • Posts: 1720
Re: 5/16 to 3/8 fuel line
« Reply #13 on: June 22, 2017 - 07:49:18 pm »
so the way the lines were set up before, the main line did not actually connect to the fuel pump, line to line...it was main line-rubber hose-fuel pump. then hard lines from pump to carb (5/16 size). it looks as if my  brother added fancy braided lines which actually look bigger than the hard lines coming from the pump, but it could be an illusion.
and at the rear (tank) i think it was also line-rubber hose-sending unit...
so i'm down to the decision of getting the proper lines from pump to carb.... the new pump to carb lines i ordered did not specify size, but they are pretty clearly 5/16. it seems as though, from this line of advice and insight, that my best option is to get new pump to carb lines to match the 3/8 main line.
and there's no way to use the 5/16 pump to carb lines along with 3/8 main line...
is that correct? I





Fuel pump to carb can be 5/16 not a problem. You would only need a 3/8 if you had an engine that made over 400 horse power.
You can keep your fuel pump too if you want.
You can connect a 5/16 pump inlet to a 3/8 main line with adaptor above, is that what you have on you fuel pump inlet is 5/16?
« Last Edit: June 22, 2017 - 08:02:27 pm by Cudakiller70 »
Auto spell I'm tired of your shirt
The above is just my opinion
Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other.
John Adams

Offline DadsCuda

  • Jr. Member
  • **
  • Posts: 73
Re: 5/16 to 3/8 fuel line
« Reply #14 on: June 22, 2017 - 08:06:17 pm »
Yes. The inlet is 5/16.
I am so glad you guys helped me with this! So many snags I'm hitting but I'm starting to get some momentum.
Thank you thank you!!