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Measure The Diameter of the Exhaust Throat - What's Your Problem?

It's All In The Return
Michael Dalton, via CarCraft.com: I have an '82 Chevy shortbed truck with a 0.030-over 350 and a 268 Competition cam. I have had a complete TPI system for 20 years that I have been wanting to put in the truck. The only things missing are the computer and wiring harness, and I know where to purchase them. My biggest holdup is the fuel system and putting in a return line. Is there a company that makes a fuel-sending unit with a fuel pump and a return line that can be used for this application? I have been procrastinating for several years, but my 18-year-old son is pushing really hard to install this system. Any help you can give me will help get him off my back.

Jeff Smith: From looking at online photos of the stock fuel-sending unit for your truck, there is a vapor return line that looks like it would work perfectly as a return line back from the engine. The ideal situation with a return line is to minimize any restriction to flow, but with a standard 45-psi system, even a 1- to 2-psi return pressure is inconsequential. That means if you have plumbed a 3/8-inch-id feed line from the tank to an externally mounted fuel pump, and the same line up to the engine, I would suggest the same size line for the return to minimize the restrictions. Of course, this move will sacrifice the vapor canister return line feature on your truck, but in looking at photos of the replacement sending unit, there may be room to install your own separate return line. Or, you could easily use a cutoff wheel on a die grinder to eliminate the original 5/16-inch vapor return tube and drill the sender out to the outside diameter of 3/8-inch tubing and braze or silver-solder a new line into the existing sending unit. If you do this, take the time to add some length to the return line into the tank and make sure the end of the return is aimed 180 degrees away from the fuel tank pickup tube. This helps minimize fuel aeration in the tank. Ideally the inlet is placed as far away from the return line as possible, but a 6- to 8-inch separation is acceptable. That is how I built my original return line setup in my '65 Chevelle and that engine makes 550 hp that I use for road racing, so I don't think you'll have a problem.

Much is written about how to mount a fuel pump, and most stories claim the pump must be located below fuel level. While this is the ideal location for pump efficiency, it is possible to mount the pump either at or slightly above fuel level and still enjoy solid pump performance. That said, pumps do a far better job of pumping and pressurizing fuel than pulling fuel vertically out of the tank. So placing the pump below fuel level is a good idea because it allows gravity to assist by pushing fuel into the inlet side of the pump. Did you know that the Model A Ford placed the fuel tank on the firewall and gravity-fed fuel to the carburetor? It doesn't get any simpler than that.

More Info
RobbMc Performance

Carson City, NV
775/ 885-7411
RobbMcPerformance.com

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