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 fuel line questions
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68bird
Sitting Bull

USA
221 Posts

Posted - 13 Jun 2015 :  12:54:12 PM  Show Profile  Reply with Quote
Hello all. I'm going to run 1/2" fuel line from the tank to the mechanical pump, and then to the carb. My questions are: would it be stupid to run half inch but leave the 3/8 sending unit? My plan was to route braided all the way with -8 AN fittings. Better options? If I replace the sending unit should I run a sock filter with an inline somewhere else? On just the inline?
I'd previously run out of fuel on the top end with my 400 so I know they'll be issues with the 461 stroker. Probably should shelf the holley 750 and run an 850 cfm carb as well?
Thanks

Robb Hermes

cortcomp
Coyote

USA
5335 Posts

Posted - 13 Jun 2015 :  2:12:04 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I'd think you'd see an improvement with the 850. Maybe running out of carb vs fuel with the 750?

Braided is rubber inside and so will deteriorate, i'd run 1/2" aluminum tube on a roll most of the way, that's how i did the 71. I also used the RobbMC 1/2" pickup for stock tanks, which doesn't use a sock filter, and his 1/2" large serviceable fuel filter that i connected to the frame in the middle of the car. I still used 3/8" to the carb, with plans to upgrade it if i had issues (i didn't). Use the braided as the flex connectors connecting the tube to the tank, tube to the fuel filter, etc. Remember to make the line from the pump to the carb a U shaped bend, try to avoid 90 degree turns and fittings if you can.
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GtoGuy32
Cochise

USA
842 Posts

Posted - 13 Jun 2015 :  4:41:59 PM  Show Profile  Reply with Quote
I second the 1/2 pickup from RobMc. Ditch the 3/8 pickup.

I run -8AN fittings on everything and half in AL lines from the stock tank all the way to my regulator. From there, I have 2 dedicated 3/8" lines that run to each fuel bowl on my 850 cfm Holley carb.

I use a Mallory pump with a big canister filter right behind the pump and have never run out of fuel on the top end.

The last thing you want to do is build a nice new engine and not feed it right.

I can post some pics of my fuel system if you are interested.

-Dave
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RayK
Cochise

USA
925 Posts

Posted - 15 Jun 2015 :  03:41:58 AM  Show Profile  Reply with Quote
You should seriously consider using an electric pump and eliminate the mechanical pump. Going with a larger carburetor will do no good if you can't feed it. If you are racing the car you may want to sump the tank as well. 1/2" aluminum is a good idea as well.

1969 Firebird 461, #62 iron heads, Comp roller, Performer RPM, Q-Jet Turbo 400 w/ Continental converter. GM 8.5" 10 bolt with 3:73 gears.11.50's@ 119+ MPH
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Phil
The Great White Buffalo

USA
7219 Posts

Posted - 15 Jun 2015 :  9:25:18 PM  Show Profile  Reply with Quote
I built an in-tank system almost 10 years ago (before they were popular) and it solved all of my fuel starvation issues without any of the drawbacks of the external electric pumps and stock/aftermarket mechanical pumps.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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GtoGuy32
Cochise

USA
842 Posts

Posted - 15 Jun 2015 :  10:11:24 PM  Show Profile  Reply with Quote
I didn't sump my tank, but race with a 1/2 tank of gas.

I did mount my fuel pump and filter below the level of the lowest point of my gas tank.

I have a fuel pressure gauge in my cab (electric, not mechanical) and it will flash red LED if my fuel pressure drops below 5 psi. I have never had a problem if the fuel level is at a 1/2 tank.

A sump will obviously be better and less sensitive to fuel level, but not look stock from behind the car.

I second the importance of a good fuel pump. I run an electric pump, but have heard that the RobMc pumps will feed high horsepower street engines 500-600 hp range.

FWIW, I posted some images of what has been working well for me.

RobMc 1/2" pickup

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Bracket to mount to stock tank straps

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Installed to tank


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Aluminum Fuel Lines

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Phil
The Great White Buffalo

USA
7219 Posts

Posted - 16 Jun 2015 :  07:17:04 AM  Show Profile  Reply with Quote
Nice work!

I like the Robbmc stuff but am a bit skeptical of how well their pumps can supply the rated quantity. Even with their nice 1/2" tank lines and running 1/2" all the way up to the mechanical pump, it is still trying to pull something forward in a fast accelerating vehicle. I played around with fuel starvation problems for many years, trying many different things including 1/2" aluminum line all the way from a welded in bottom sump/bottom sucker to various mechanical pumps. Even a Carter electric as an on/off pusher. Nothing worked perfectly. There were improvements but the car still nosed over at the top of first gear and half way through 2nd.

The in-tank setup (with new 3/8" steel line I bent up!) solved everything. I installed a discreet fuel pressure gauge and have it right in the corner of my windshield atop the dash so I can see it at all times. It hardly fluctuates regardless of my driving. The pump is just a Walbro drop in replacement (255 l/hr) for an 86-87 Buick GN.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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68bird
Sitting Bull

USA
221 Posts

Posted - 16 Jun 2015 :  10:14:00 AM  Show Profile  Reply with Quote
I like the robbmc 1/2" pickup and will probably go that route with aluminum lines. Do you guys really feel it necessary to go with an electric fuel pump? The car will hardly, if ever see any strip time. My current 3/8 line is all cobbled together from the previous owner with a mix of hardline and rubber hose splices with clamps. It's ugly, an accident just waiting to happen.

Robb Hermes
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Blued and Painted
Chief PONTIAC

USA
3406 Posts

Posted - 16 Jun 2015 :  11:42:54 AM  Show Profile  Reply with Quote
Weak valve strings can also make it nose over.

Cobbling will reduce flow. If the 3/8 factory steel line is not usable, an upgrade is warranted.

In my opinion only,, The weight of a 1/2" column of fuel is much greater than a 3/8" column of fuel. SO any mechanical pump up front will have trouble pulling the extra weight of fuel @ 1/2 of one G force or more.

If a 1/2" line is installed pumping from the back and regulating from the front is a good idea..

I have no trouble with a factory 3/8's fuel system set-up on my 461. knock on wood.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 16 Jun 2015 12:06:42 PM
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68bird
Sitting Bull

USA
221 Posts

Posted - 16 Jun 2015 :  5:53:01 PM  Show Profile  Reply with Quote
blued and painted, what are you running for a pump? Ya I don't have a clue what he was thinking. Some of the rubber hose bends are actually looking to kink off. Once I knew about the line that's what I blamed my nose dives on while at the top end.

Robb Hermes
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