I am currently in the process of switching from factory carb to the Holley Sniper EFI. Since my ’84 TA did not have the EFI tank I have purchased a new unit for an ’89 5.7L and the sending unit to install the intake fuel pump. I also purchased the Walbro pump kit 5CA400HP (255ltr) and 20' of Earls 3/8” Vapor Guard EFI hose & clamps. I will be using the existing 3/8" stock hard line (orig feed line) for the return... my concern is with the sending unit return line is only 5/16”. I have heard that the return line should be an equal size as the inlet or there would/could be pressure buildup especially when the tank is full (since that return goes to the bottom of the tank).

Your thoughts

 

After looking at the sending unit I see that there is a 3/8” line for the tank pressure valve ( the one that is mounted above the axle). I was thinking of converting this with an added 3/8” hard tube to the bottom of the tank and using the smaller diameter vapor line (after removing the rollover check valve) for the pressure valve. This of course would mean that the vapor canister would need to be unused/removed and the 5/16” sending unit return line would need to be capped off. (Note - all emission hardware has been removed due to damaged & inoperable components and connectors over its 34 years of operation). This is not a daily driver and is will be used for fun & show.

Your thoughts?

 

I edited my post because I reread your original post and I see you do plan to use an in tank pump

 

TTT (to the top)
Ideas on this anyone?

 

5/16 is plenty big. We don't upgrade 5/16 supply/return lines till we are going over ~600 HP. It will flow what you need.

GD

 

General Disorder ~
Thanks for the input. I have just heard and read many that say with all the bends and small barb ends on the 5/16" line that it is just asking for trouble (back pressure). The ID of the return line at the barb end is only .225 dia. Would it be better to cut off the barb and put on a Earls compression fitting that converts from a 3/8 hose (orig stock hard line feed line) to a 5/16 full dia on the sending unit? I don't think I will get a good seal clamping the Earl's Vapor guard 3/8"tubing to the 5/16" barb.

Yours and anyone else thoughts are very welcome

 

I converted over to EFI 3 years ago and installed the Holley Terminator system and like you, I put a new tank, along with the in-tank pump. I didn't eliminate the vapor canister since the fuel system is still a closed system and I didn't want to have the tank pressurize, which is what happened, so I vent my canister just below the steering box and stuck a small import style filter on the end. I didn't change any of the sizes when it comes to fuel lines and I have never had any issues with the car running short on fuel pressure or volume.

 

...since my 89 vent canister was originally controlled by the ECM, and since I switched to Holley HP EFI, I had no way to control the venting. I built a charcoal filter to remove the gas smell from the open vent. Works great. I change the charcoal with fishtank charcoal about twice a year.

 

You can do some research on the google if you don't believe me, but your 1/4" ID line will easily support 500+ HP with a quality, high volume fuel pump. You are worrying for nothing. Just run it. This is not a low pressure carbureted application. With EFI the fuel line sizing is much less of an issue. I guarantee that the orifice in the pressure regulator is much smaller than 1/4"

GD