Ask Away with Jeff Smith: Shoebox LS and Proper EFI Fuel Pump Placement

Jeff Smith got a couple of nice meaty tech questions this month. Grab a fork and dig in.

LS Swap in a 1955 Chevy
A certain J.P. wanted to swap the tired 283 V8 for a 4.8L LS V8 he got a great deal on from a buddy. He also wanted to know if it's better to stick with a carburetor or go with the factory EFI system.

As Jeff explains, the actual physical swap is pretty easy as companies like Trans-Dapt make the necessary engine and transmission mounts. The devil is in the details, as they say. The carburetor option is the easiest, requiring not much more than the carb, intake, an ignition control box, an electric fuel pump, and a fuel pressure regulator.

The factory EFI route gets more complicated. Jeff explains the need for the wiring harness and electronic throttle pedal assembly from the donor vehicle, plus some sort of in-tank fuel pump setup with the required plumbing.

Either way, Jeff says, J.P. will need to fabricate an exhaust system and probably replace the oil pan with a low profile pan from an LS Camaro or one of the aftermarket 'musclecar' swap pans. A lot to consider, for sure.

External or In-Tank Electric Fuel Pump?
P.T. has a 1969 Mustang that he is thinking about converting to a throttle body-style EFI system. He would rather use an external electric fuel pump, which would be easier to install and cost less than an in-tank pump.

According to Jeff, you can indeed use an external fuel pump, but stay away from a simple inline pump. He recommends using one of FiTech's or Edelbrock's external fuel sump systems. These are basically a small fuel tank with a high pressure fuel pump inside. You plumb the engne's mechanical fuel pump to the sump, where the internal pump boosts fuel pressure the required amount and then sends it to the throttle body. Jeff explains all of the pros and cons of the external sump in the column.