Fuel return line diameter?
#1
Fuel return line diameter?
What was the original 3rd gen F-body carbureted V8 fuel return line diameter? The places that sell the so-called "reproduction" fuel lines are selling 5/16" return lines for the carb equipped cars, the same diameter as fuel injected return lines, but shouldn't carbed cars' return lines be 1/4" like the return line port on the original style mechanical fuel pump is? Also, my GM G-body catalog shows 1/4" for carbed fuel lines, plus the picture in my 1986 Camaro assembly manual shows the return line being significantly smaller than the 3/8" fuel supply line.
#2
Supreme Member
iTrader: (1)
Join Date: Sep 2005
Posts: 26,078
Received 1,676 Likes
on
1,272 Posts
Car: Yes
Engine: Usually
Transmission: Sometimes
Axle/Gears: Behind me somewhere
Re: Fuel return line diameter?
In our cars, the return line was 5/16", the same as the port on the fuel pump.
It was ¼" in many older cars, esp those that the return originated off of the filter rather than the pump, but not ours.
There's no benefit to making it smaller.
It was ¼" in many older cars, esp those that the return originated off of the filter rather than the pump, but not ours.
There's no benefit to making it smaller.
The following users liked this post:
T.L. (04-24-2024)
#3
Re: Fuel return line diameter?
#4
Senior Member
Re: Fuel return line diameter?
He was answering your question about the return line on your car (and I believe he was correct, if your lines are original.)
Now the sizes you might find on your aftermarket replacement pump made in China or Mexico, yes that could be whatever size that manufacturer chose to use. BTW that pump you bought for your 1980s car also is made to fit a WIDE variety of other GM cars and trucks, probably spanning a period of at least 2 or 3 decades. So yes, it is no surprise if the line off your new pump is 1/4". It's okay, will still function just fine.
Now the sizes you might find on your aftermarket replacement pump made in China or Mexico, yes that could be whatever size that manufacturer chose to use. BTW that pump you bought for your 1980s car also is made to fit a WIDE variety of other GM cars and trucks, probably spanning a period of at least 2 or 3 decades. So yes, it is no surprise if the line off your new pump is 1/4". It's okay, will still function just fine.
#5
Re: Fuel return line diameter?
He was answering your question about the return line on your car (and I believe he was correct, if your lines are original.)
Now the sizes you might find on your aftermarket replacement pump made in China or Mexico, yes that could be whatever size that manufacturer chose to use. BTW that pump you bought for your 1980s car also is made to fit a WIDE variety of other GM cars and trucks, probably spanning a period of at least 2 or 3 decades. So yes, it is no surprise if the line off your new pump is 1/4". It's okay, will still function just fine.
Now the sizes you might find on your aftermarket replacement pump made in China or Mexico, yes that could be whatever size that manufacturer chose to use. BTW that pump you bought for your 1980s car also is made to fit a WIDE variety of other GM cars and trucks, probably spanning a period of at least 2 or 3 decades. So yes, it is no surprise if the line off your new pump is 1/4". It's okay, will still function just fine.
I don't think that GM would have used any different fuel pumps on 3rd gen F-bodies than they did for other makes getting the LG4 engines. I'm sure the same 305's that went into Firebirds and Camaros also made their way into Caprices and Monte Carlos.
Also, I don't understand what the point would have been to use as large as 5/16" fuel return lines on carbureted cars. I suspect very little fuel needs to returned to the tank with a carbed car using a mechanical fuel pump. Cars were made without fuel pumps with return ports for decades before they started using ones with return ports them in the late 70's. I suspect the extra return port was added to mechanical fuel pumps as much to help prevent vapor lock as anything else.
#6
Member
Re: Fuel return line diameter?
My 82 lg4 had 3/8 feed and 5/16 return. My dad had an 82 crossfire. It had the same size lines. Now I have 3/8 feed and returns cause that's what EFI needs. There is no reason to neck it down. 5/16 rubber line should fit on there. If not, something isn't right.
#7
Re: Fuel return line diameter?
I still can't see the sense in using a 5/16" return line when a 1/4" one will work just fine, as evidenced by all the cars that have had 1/4" return lines.
Trending Topics
#8
COTM Editor
iTrader: (22)
Join Date: Mar 2001
Posts: 9,910
Likes: 0
Received 1,857 Likes
on
1,272 Posts
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: Fuel return line diameter?
What is your purpose in asking the question?
#9
Supreme Member
iTrader: (1)
Join Date: Sep 2005
Posts: 26,078
Received 1,676 Likes
on
1,272 Posts
Car: Yes
Engine: Usually
Transmission: Sometimes
Axle/Gears: Behind me somewhere
Re: Fuel return line diameter?
The Carter M6626 ... has a return port that is only 1/4" diameter.
I still can't see the sense in using a 5/16" return line when a 1/4" one will work just fine
I thought you asked what size THE CAR has, not all that other know-it-all crap. Stay focused.
#12
Supreme Member
iTrader: (8)
Join Date: Oct 2001
Location: Il
Posts: 11,708
Received 756 Likes
on
512 Posts
Car: 1989-92 FORMULA350 305 92 Hawkclone
Engine: 4++,350 & 305 CIs
Transmission: 700R4 4800 vig 18th700R4 t56 ZF6 T5
Axle/Gears: 3.70 9"ford alum chunk,dana44,9bolt
Re: Fuel return line diameter?
Larger line, less restriction.
if you're doing a show or 100% correct restoration that requires the line to be 1/4" then pursue that. Especially if your car is 82-84. After that, it could be larger metric ( 5/16 =8mm) like a lot of other things that went metric in 84.5.
could be any number of reasons the f-car used different line than other cars. Does it matter that fuel gets back to tank faster with the bigger line?
if you're doing a show or 100% correct restoration that requires the line to be 1/4" then pursue that. Especially if your car is 82-84. After that, it could be larger metric ( 5/16 =8mm) like a lot of other things that went metric in 84.5.
could be any number of reasons the f-car used different line than other cars. Does it matter that fuel gets back to tank faster with the bigger line?
#13
Member
Re: Fuel return line diameter?
The fuel will be cooler w the larger line, it's also less resistance on the pump (probably not an issue on stock power) The 5/16 is what was run in 82-84 v8 cars also, so a 100% resto would want period correct. The 3/8 looks larger than the 5/16 because it is. The sender in the tank has 3/8 and 5/16 lines coming out of it. So if you convert to 1/4, you're gonna need to neck it up somewhere.
#14
COTM Editor
iTrader: (22)
Join Date: Mar 2001
Posts: 9,910
Likes: 0
Received 1,857 Likes
on
1,272 Posts
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: Fuel return line diameter?
Life is full of really hard decisions like whether you buy a perfectly functional 5/16" return line.
The following users liked this post:
TTOP350 (04-26-2024)
#16
Senior Member
Re: Fuel return line diameter?
Thread
Thread Starter
Forum
Replies
Last Post
GASGZLR
Tech / General Engine
12
10-24-2003 06:46 PM