Fuel pump contacting block

[cudabob496]

1/4 npt matches up well with 3/8 line, I think.

http://www.engineersedge.com/hardware/taper-pipe-threads.htm


The fittings I used for this pump were 1/4NPT x 3/8 inch

http://www.summitracing.com/parts/crt-m4862/overview/

[mopar jack]

Pipe sizes are generally related to their inside diameter while tubing  is related to the outside diameter. So the tubing inside diameter will be less minus the wall thickness.

[cudabob496]

less minus twice the wall thickness?

[mopar jack]

I agree

[msbaugh]

I just found out the fuel filters I bought have 5/16" inlet and outlets. SOB!

[mopar jack]

5/16 is what I have on my 440-6. The fuel line at the carb is 5/16

[734406pk]

I just found out the fuel filters I bought have 5/16" inlet and outlets. SOB!

The pressure side filter and vapor separator is 5/16"  in and out with a 1/4" return line connection.

[cudabob496]

5/16 is what I have on my 440-6. The fuel line at the carb is 5/16

Seems 3/8 would be a minumum for you. Per Holley,flowrate
is more important than pressure.

[734406pk]

Re plumb and give it a try. The 1/4 " return line may solve your vapor lock problem.

[Strawdawg]

Use an adapter to drop the line to the smaller size.  5/6" can push close to 500 hp and the shorter length, if you change to a smaller line to the carb will not hurt too much.  As already noted, the return line will keep the fuel cooler and a good spacer under the carb will help a lot as well.

[ff6849]

http://www.cuda-challenger.com/cc/index.php?topic=91035.msg900647#msg900647

I had the same issue (vapor locking), I finally just went to a full return system tried to use the 1/4 vapor line as my return had issues regulating fuel pressure,  the regulator is designed to work with equal size lines. I ran two 3/8 fuel lines and had a bung welded into the side of the fuel tank. Running a Holley blue pump, a little on the noisy side but only really noticeable at when at a stop while cruising i don't notice it. The car run much better with this set-up.     

[msbaugh]

I'm not wanting to use an electric pump though, so I'm trying to make this return system work with the smaller return line and my mechanical pump.

According to Holley, You can't run a bypass regulator with a mechanical pump.  I've spent some time this past week getting this set up... Will post pictures soon

[msbaugh]

This is my last and final trial to make this work with the mechanical pump!!! I did some rather un-orthodox routing of my fuel line... Which I won't mention due to ridicule and scolding online.. No doubt it would fail a nhra tech inspection, but I don't give a ****!

Fuel line is a good distance from my headers and my return line has been routed back to the sending unit! The filter is downstream of the pump on the pressure side. The outlet goes straight to my regulator them to my carb. Check out the pictures and let me know what you think. It doesn't look good at all... But keep in mind, this is experimental and there's less than 8" of rubber line on the whole thing. I'll fill her up, check for leaks, and report results tomorrow!!

[msbaugh]

I've eliminated vapor lock with this setup!!!

 Only there's still a problem. My fuel pressure will not go above 3-1/2 psi unless I get on the throttle, I think it's because I have that regulator downstream of where the return splits off... If I pinch the return line shut fuel pressure jumps up to 6 psi.

I have two options as I see it, I know fuel is recirculating preventing vapor lock. Either I eliminate the regulator all together and see what pressure does, or I move the return downstream of the regulator and plumb the return frpm a t fitting at the carb

[734406pk]

Well Done Sir! Does your fuel filter/vapor separator have a restriction orifice (.065")on the 1/4" return line? If not, or its too big, you can make one easily. Or you can remove the FPR and try running without it, checking the max fuel pressure.