Fuel question
Thread Starter
Racer
Joined: Apr 2010
Posts: 352
Likes: 1
From: Central NJ
Fuel question
Hey guys. I recently dropped a 468ci motor into my 74. When the motor was built I wanted to run a mechanical pump since I wasn't aiming for huge numbers but my mind has since changed and it became a ***** to the wall build. I will swap over to an electric pump in the future when I have more money to spend but for now I'd like to be able to enjoy my car for the summer. Anyway, I opted for an Edlebrock mechanical pump and installed it assuming everything would work just fine. The pump was quite large and I had to take it apart and rotate the base of it in order to get it past the frame. Once installed it fit and looked great but then I realized there is only 1 spot for a fuel fitting and I had 2 lines. I came on here to see what that smaller line was for and it turns out it's a vapor return line. My question is, what direction is the gas being vented? Does it go pump to tank or tank to pump? I would assume the pressure would be being relieved from the tank and moving to the pump but everywhere I look they call it a "return line" and usually return lines go from pump to tank. Can anyone provide me some info on that? Ideally I would like to simply "delete" it by not hooking it up but I'm sure it's not that simple.
Pro
Joined: Oct 2009
Posts: 523
Likes: 4
From: Calgary Alberta
Hey guys. I recently dropped a 468ci motor into my 74. When the motor was built I wanted to run a mechanical pump since I wasn't aiming for huge numbers but my mind has since changed and it became a ***** to the wall build. I will swap over to an electric pump in the future when I have more money to spend but for now I'd like to be able to enjoy my car for the summer. Anyway, I opted for an Edlebrock mechanical pump and installed it assuming everything would work just fine. The pump was quite large and I had to take it apart and rotate the base of it in order to get it past the frame. Once installed it fit and looked great but then I realized there is only 1 spot for a fuel fitting and I had 2 lines. I came on here to see what that smaller line was for and it turns out it's a vapor return line. My question is, what direction is the gas being vented? Does it go pump to tank or tank to pump? I would assume the pressure would be being relieved from the tank and moving to the pump but everywhere I look they call it a "return line" and usually return lines go from pump to tank. Can anyone provide me some info on that? Ideally I would like to simply "delete" it by not hooking it up but I'm sure it's not that simple.
I recently went through the same issue when I installed my 427 SBC into my 77. The engine came with the Edelbrock mechanical pump and I had to clock the base to clear the frame and allow the connection of the fuel line.
I noticed there was only one fuel line connection on the pump but two fuel lines in the car. Apparently there is a supply line and a return line. Accordingly to my 77 AIM book the return line goes back to the fuel tank.
After reviewing many posts in the forum I have decided to plug the return line and see how the car runs. According to information provided the return line was built into our cars to prevent vapor lock and boiling of the fuel when the car is sitting in traffic on a hot day.
I personally have not experienced this in my car yet, but if I do then I may have to look at installing a correct SBC Corvette fuel pump or an aftermarket electric fuel pump with the return line feature.
Apparently there is a post here from Lars that shows a system work around, but I think it maybe more work than just replacing the pump with one that allows for a return line. Hope this info. helps.
Thread Starter
Racer
Joined: Apr 2010
Posts: 352
Likes: 1
From: Central NJ
Thanks for the info! I'm glad there are other guys overcoming the same obstacles as me lol. Would you mind keeping me posted on how it runs after plugging the return line? I'm going to button up the rest of my car and then try it myself but if you get around to it first I'm curious to hear how it goes. Hopefully it runs okay and I can enjoy a big horsepower C3 this season and swap to electrical for next year. Assuming I don't blow all my money on my T56/Doug's rear end swap hahaha.
Thread Starter
Racer
Joined: Apr 2010
Posts: 352
Likes: 1
From: Central NJ
Thank you for your input but with the setup I'm going with there's no way the stock fuel pump would have been able to keep up. Had this been a stock/mild build I would have certainly gone with it.
