Do Q-jets require a fuel return?

[markedmondson]

This question came up on the NCRS Forum.

A member wants to use a Q-jet and spread bore manifold on a crate small block in a '63 Corvette.

Most cars I've seen originally equipped with a Q-jet have a fuel return line, either from the pump or from an in-line fuel filter. 

Does this mean a fuel return is needed by the Q-jet?  Maybe to provide proper volume or pressure? Or is this not a concern? 

It's a question for this swap because '63 Corvettes are not plumbed with a fuel return.

Thanks.

[carmantx]

We haven't used a return line on our personal cars we have built for Quadrajet use.

[Ethan1]

We haven't used a return line on our personal cars we have built for Quadrajet use.

 Neither have I.

[Cliff Ruggles]

Factory fuel return lines were used for A/C cars with Q-jets, but there are exceptions to that.

It's never a bad idea to use a return line, even though many set-ups work fine "dead head".

I use a return line with my set-up, sumped tank, high flow Marine spin on filter assembly, Mallory 140gph electric pump, 8an lines fittings everyplace to a return regulator just in front of the Q-jet.

I tried that deal "dead head" and it worked fine, but the pump burned up the brushes in about 2 months of use.  Installed the return system and nearly 20 years later the pump is fine after the new brush install.......Cliff

[markedmondson]

Thanks guys; I appreciate the help.

I posted a link to this thread on the NCRS Forum as an answer the member's question.

[qjetsrule]

Cliff,
Do you happen to have a picture of your plumbing at the carb you can post? Thanks

[Cliff Ruggles]

Don't have any pics of it.  Pretty simply set-up.  I tap the OEM fuel filter housing for 1/4"NPT threads and install a 1/4NPT to -8 fitting.  Since everything in the rest of the system is 1/4" NPT, they get the same fittings as well. 

I use a standard $20 Holley regulator and built my own return just before it.  Nothing more than a 1/4 x 1/4 x 1/4" NPT "T" screwed directly into the bottom of the regulator.  I come out the side fitting and reduce it down for the factory return line.  The fuel takes the path of least resistance to returns to the tank constantly to take some load off the pump.

I tested the line to the carb and it will fill a gallon jug pretty quickly so no problem keeping up with my engine making over 550hp/600tq.

I'd also add that the fuel pump is very quiet once the return system was added.  It made a LOT of noise and grumbling when set up "dead head", even though Mallory says you can run them that way. 

Seems to be quite a few opinions on the Boards for this topic.  Every time you mention running a return someone jumps in and says they have been running "dead head" with a high output electric pump for nearly 50 years and zero issues anyplace. 

My pump lasted about 2 months, which included about 100 track runs and maybe 500 street miles.  Same exact pump with a new brush set still lives nearly 20 years after the return system install and dead quiet.....FWIW......Cliff

[Hillbillyenginering]

Cliff
This was good info. I'm dealing with issues with my 66 toro. I was building a new fuel system and was planning it and looking for options. Plan to follow this except -6n fittings. Not racing and close to stock.

[Cliff Ruggles]

Good plan as there are no negatives that I know of using a return system.  Especially for a street driven car that spends a good amount of it's time sipping small amounts of fuel while the fuel pump continues to make full cycles and move tons of fuel needed for hard runs.

Why not return the unused fuel to the tank to keep it cool and take some load off the pump?

I've never had the first issue once with my return system, but as mentioned above running "dead head" quickly fried my high volume electric pump.......Cliff

[55 Tony]

Cliff mentioned to "keep it cool", that is exactly why I run mine with a return.  My return is using a fuel filter (I think for a jeep) that is made to let vapor go out the return first.  I used to have major problems with sort of vapor lock on hot days and this helped immensely.  Don't skimp on the return line, make it at least as big as the feed from the tank.  I still have some problems when the gas stations change over to winter fuel and we have a hot day, but that is the exception.  My setup works with a high volume mechanical fuel pump.

[markedmondson]

For OEM designs I've seen on GM cars, the fuel return line is smaller than the supply line.

[Schurkey]

For OEM designs I've seen on GM cars, the fuel return line is smaller than the supply line.

5/16 or 3/8 fuel supply tubing, 1/4" vapor return.  The vapor system is typically restricted to about .060 in the fuel pump.  Actual vapor passes easily, but it acts like a carb jet for liquid fuel.

It's been a LONG time since I've seen the fuel filters built to connect the vapor return tube to.  I think they're also restricted on the vapor outlet.

[blazer74]

I run the filter with the vapor port up close to the carb. otherwise I have vapor lock issues.
Wix 33041 3/8 in/out with 1/4 vapor port. Has a .060 orifice.
There's a 5/16 in/out version also.
I have not tried the pump with the vapor port.

[markedmondson]

Does someone make an in-line filter with a bypass that screws directly into the carb's inlet?  With the steel line attached to the other end, this would avoid any rubber hose on the pressure side.

I saw a car for sale on eBay awhile ago with a filter like this, but without the bypass.  It stuck out about 3" from the Q-Jet's inlet with the steel supply line directly attached to the filter's inlet. It was a Chevy with the inlet pointed to the right.  Haven't seen that before.