Question re: conversion to EFI - return line?
Thread Starter
Melting Slicks
Joined: Jan 2000
Posts: 2,386
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From: far, far away
Question re: conversion to EFI - return line?
This question is directed to those among you who've converted your C3 to fuel injection, although the '81 and '82 owners may know about this, too.
My '81, with its stock fuel system, has two lines between the tank and the fuel pump. The larger of the two is the supply line. I can only assume the other one is a return line. I don't understand why a carbureted car with a mechanical pump running, like, 6 psi of fuel pressure needs a return line. 'Splain, please? :confused:
And here's the real question: If I were to ever get a serious wild hair about converting to EFI (I've always wanted to put a TPI on my crate motor!) would that second line be adequate as a fuel return line for the EFI system? Being able to keep my mods in the engine compartment would be a significant simplification to the conversion, it seems to me...
TIA! :flag
My '81, with its stock fuel system, has two lines between the tank and the fuel pump. The larger of the two is the supply line. I can only assume the other one is a return line. I don't understand why a carbureted car with a mechanical pump running, like, 6 psi of fuel pressure needs a return line. 'Splain, please? :confused:
And here's the real question: If I were to ever get a serious wild hair about converting to EFI (I've always wanted to put a TPI on my crate motor!) would that second line be adequate as a fuel return line for the EFI system? Being able to keep my mods in the engine compartment would be a significant simplification to the conversion, it seems to me...
TIA! :flag
Race Director
Joined: Mar 2001
Posts: 11,322
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From: Living in the Hartland
Re: Question re: conversion to EFI - return line? (Gator81)
The stock return line is too small but the vapor cannister return line is large enough, it is on the drivers side in my 73, not sure if got one in your 81.
Le Mans Master
Joined: Aug 2000
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From: Semper ubi, sub ubi
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Re: Question re: conversion to EFI - return line? (Gator81)
Many 'vettes had a return line as far back as 1968, that I know of. Some of the mechanical pumps had a return line built in to them and some cars (my 69) had a small return line exit the filter. I assume that this was part of the pressure control on the pump itself.
I've been led to believe that the line itself is too small to work as a return line for a TPI conversion.
Some 'vettes actually have another line returning to the tank that is large enough, it is exit the charcoal canister. I think Zwede used this line for his return when he converted to TPI last year. I considered a TPI conversion in the past, I planned on using the old feed line for the return and add a new line for the main fuel line.
Some people have used stainless steel braided armored hose for fuel line, it is easy to use and fairly secure, at least much better than rubber fuel line. The other alternative is to replace with steel tubing, it can be done with the car still on the frame but it will take some creative manuvering to do it.
I've been led to believe that the line itself is too small to work as a return line for a TPI conversion.
Some 'vettes actually have another line returning to the tank that is large enough, it is exit the charcoal canister. I think Zwede used this line for his return when he converted to TPI last year. I considered a TPI conversion in the past, I planned on using the old feed line for the return and add a new line for the main fuel line.
Some people have used stainless steel braided armored hose for fuel line, it is easy to use and fairly secure, at least much better than rubber fuel line. The other alternative is to replace with steel tubing, it can be done with the car still on the frame but it will take some creative manuvering to do it.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Re: Question re: conversion to EFI - return line? (Gator81)
I have found the 1/4 inch carb return line to be just fine for the return to the tank....no pressure/delivery problems from using the stock steel lines that were on my '72....now I use Erols hose double clamped on the steel lines..and adaptor fittings on the TPI setup....
GENE
GENE
Burning Brakes
Joined: Apr 1999
Posts: 1,161
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From: Texas
Re: Question re: conversion to EFI - return line? (Gator81)
Or you could run new 1/2" braided line beside the stock supply line as a new F/I supply line and return using the stock fuel supply tube. That's what I did on my '73 and it works fine. That also leaves your vent line and cannister intack and functional.
good luck
dr
good luck
dr
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Question re: conversion to EFI - return line? (DavidR)
Or you could run new 1/2" braided line beside the stock supply line as a new F/I supply line and return using the stock fuel supply tube. That's what I did on my '73 and it works fine. That also leaves your vent line and cannister intack and functional.
good luck
dr
good luck
dr
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Racer
Joined: Aug 2001
Posts: 356
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From: Glacier County mt
Re: Question re: conversion to EFI - return line? (Gator81)
Don't use a small line for the EFI return. Use the same size line as the feed from the fuel pump. Use of a small return line will cause problems at low RPM / low engine load conditions..
I found out the hard way!
:crazy: :banghead: :crazy:
I found out the hard way!
:crazy: :banghead: :crazy:
Intermediate
Joined: Aug 2001
Posts: 41
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From: Hereford Az.
Re: Question re: conversion to EFI - return line? (Gator81)
My opinion is that the return line was desgned to circulate fuel to keep it cool and avoid the dreaded vaper lock problem.
Andy Anderson
Andy Anderson
