need for a fuel vent line?
Thread Starter
Pro
Joined: Apr 2015
Posts: 553
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From: Warrington PA
need for a fuel vent line?
I'm in the middle of cleaning up a 74 and was going to ditch the stock fuel line & vent (return) line in Lew of #6 AN Teflon lined flexible stainless steel fuel line. So what did they have it on the cars anyway, I see no need for a return vent line?
I also drag race and the only time we run return lines is when we need a steady "set" psi to a barrel valve or NOS solenoid and not have the psi "dead head". but for what I have in my car now, a 355 with a 600 holley I see no need for it.
I also drag race and the only time we run return lines is when we need a steady "set" psi to a barrel valve or NOS solenoid and not have the psi "dead head". but for what I have in my car now, a 355 with a 600 holley I see no need for it.
Last edited by Lyndwood; May 2, 2015 at 03:25 PM.
Old Fart Pilot
Joined: Apr 2010
Posts: 1,932
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From: Spokane, WA
Not an expert (that's for SURE) and to prove it I'll admit I don't understand what you're asking. On my '71 I have a fuel return line AND a separate vent line. The return line runs from the fuel pump along the right frame rail back to the tank (right next to the fuel supply line). The vent line is on the other side of the car. Is this what you have on the '74? Which of these are you thinking of removing? I've heard of people removing the VENT line, but it was always noted that a vented fuel tank cap would then be necessary.
FWIW (which probably isn't much)
paul
FWIW (which probably isn't much)
paul
Thread Starter
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Joined: Apr 2015
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From: Warrington PA
I am referring to the return line back to the fuel tank that runs with the supply line. I am going to remove that and just have one supply line to the front. I assume the fuel tank has a vent line as well off the top of the tank, haven't looked into that yet?
my question was why did they have the return line on the car in the first place, I could see it on a Fuel injection set up but not a carb set up? what was the factories reason for it?
my question was why did they have the return line on the car in the first place, I could see it on a Fuel injection set up but not a carb set up? what was the factories reason for it?
Melting Slicks
Joined: Feb 2006
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From: Sunrise FL
If you look in the archives there are lots of different ways of doing this, but the best place for the return is at the carb. Some guys have added a small restriction in the return line. Obviously you don't want to return too much back to the tank!
Race Director
Joined: Apr 2009
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From: Charlotte NC
The return line purpose is to return excess fuel and vapors to prevent vapor lock. That is fuel boiling in the lines.
If you look in the archives there are lots of different ways of doing this, but the best place for the return is at the carb. Some guys have added a small restriction in the return line. Obviously you don't want to return too much back to the tank!
If you look in the archives there are lots of different ways of doing this, but the best place for the return is at the carb. Some guys have added a small restriction in the return line. Obviously you don't want to return too much back to the tank!
All Corvettes after 1967 had fuel return. THEN...fast forward to the NEW Corvettes where the fuel filter is located in the rear of the car...and has the fuel return provision...BUT...there is only one line feeding the fuel injection system. Do not ask me why they allow such a long line going to the engine....but I am sure they have also figured out WHERE to route it so it does not get HOT. Who knows...GM may change it and have the fuel return line back up on the fuel rails like the previous Tuned-Port and LT-1 /LT-5 engines.
DUB
Melting Slicks
Joined: Oct 2003
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From: Chapel Hill NC
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It is my understanding a return fuel line will diminish the possibility of vapor lock. Based on my personal frustrating experience chasing vapor lock problems in the past, I would not remove the line.
Thread Starter
Pro
Joined: Apr 2015
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From: Warrington PA
The return line purpose is to return excess fuel and vapors to prevent vapor lock. That is fuel boiling in the lines.
If you look in the archives there are lots of different ways of doing this, but the best place for the return is at the carb. Some guys have added a small restriction in the return line. Obviously you don't want to return too much back to the tank!
If you look in the archives there are lots of different ways of doing this, but the best place for the return is at the carb. Some guys have added a small restriction in the return line. Obviously you don't want to return too much back to the tank!
thats what we do on our race cars too, we have a return block before the fuel tank that the return line goes to. It has an orifice in it that allows fuel to return and bleed off and not just be a return "dump" fuel to the tank.
we don't have any vapor lock problems but then again we are not driving on the street with our race cars LOL. since this is my first vette and members have noted vapor lock problems I may consider leaving the return? I assume c3's have inherent under hood heat problems?
thanks you all for your thoughts & advise!
Burning Brakes
Joined: Oct 2008
Posts: 1,037
Likes: 14
From: Mobile Alabama
For street driving (in most climates) the return helps with vapor lock/percolation problems - today's fuel blends dont help. If you look at the "ideal" system for performance, whether carb or injection, you would want the coolest fuel (dense) and fuel pressure to be accurate at the point of use. This would correlate to a regulator at the carb or injectors, and a return back to the tank. Fuel sitting in the line on the engine gains heat - using a cool can and return does work. Chevy went to the rear regulator/return on cars a few years ago for emission laws, not for performance. The new injected cars run much higher pressure, so the boiling point is raised.
Do you have to have a return? No
Is a return better in most situations? Yes
Do you have to have a return? No
Is a return better in most situations? Yes
Last edited by 74modified; May 3, 2015 at 09:26 AM.
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I understand the return line , the thing I do not understand is why/ how LT1 ?
did not have return line? ...on a high performance motor, why the change ?
did not have return line? ...on a high performance motor, why the change ?