In-Tank LS Swap Fuel Pump: Heart of an EFI Conversion Fuel System

Then, somewhere in the 1980’s, electronic fuel injection supplanted carbs as a more efficient way to mix fuel and air. These systems needed the fuel fed to the injectors at a higher pressure so it could be atomized without the aid of the venturis and pressure differentials that made a carburetor work. Early TBI systems took somewhere around 15 psi, with more modern LS-swaps requiring around 58 psi of fuel pressure. Not to mention that EFI also ushered in a new era of high performance, with newer engines capable of more power than ever thought possible in the old days and therefore requiring a greater volume of fuel as well. As these modern engines are swapped into older cars, some sort of electric fuel pump is necessary to match the increased demand of the modern powerplant.

That brings us to the ever-popular LS swap. The Gen-III LS swap is the hot ticket to add big power and reliability to your classic. But that late model power is going to require a dedicated LS swap fuel pump. The video below highlights the Speedway Motors electric fuel pump conversion that we chose as an EFI swap fuel pump for the 5.3 LS in our project ’68 C10.

We chose an in-tank fuel pump to compliment the EFI fuel tank conversion on our C10 project. The fuel tank not only moved the stinky old tank from behind the seat, it also came out of the box with a ring on it ready to mount an in-tank fuel pump. The above video details the assembly of our Universal In-Tank Electric Fuel Pump Module. As expressed in the video, there are some details to consider as you are assembling this pump module.

First, always measure twice and cut once. Our universal pump module will go all the way to 16” in depth, so most typically you’ll need to cut the bracket down to work in your tank. You’ll want the pickup as close as possible to the bottom of the tank. We gave ourselves about 1/8” of clearance to the bottom of the tank to be sure that the base wasn’t holding the top plate off the tank and causing issues with the gasket surface. Once you cut, be sure to clean up and de-burr to avoid getting any chips in the clean new fuel tank.

Assembly is fairly straightforward and the included instructions are very helpful. Here are a few specific notes that we’ve found to be critical with this assembly. First, be sure to use hose clamps on the hose from the pump to the top plate. We’ve had these separate from the pump before when assembled without clamps. Also, be careful to insulate the electrical terminals from the top plate as detailed in the video. In general, take extreme care in assembly, as the fuel pump is obviously a critical component and it will likely be difficult to remove and service once it’s in the car. Never forget the importance of safety when planning and building your fuel system. Consulting the DOT rules that govern fuel tanks and fuel systems is a great place to start.

The first major advantage of an in-tank pump for LS swaps (and others) is that the pump is literally immersed in in fuel. This setup is advantageous for several reasons. First, the surrounding fuel cools and lubricates the pump. This can be tremendously helpful in keeping that hard-working pump alive. Ever wonder why the OE’s primarily use this setup? Another advantage of an in-tank setup is that the surrounding fuel and the tank itself serve to quiet the pump operation. Some of us don’t mind the rattling and buzzing of a big external pump, but sometimes all that racket can get old in a car that gets lots of street use.

In-tank pumps are also usually self-contained units that can simplify fuel system plumbing and mounting. Once the pump is dropped into the the LS swap fuel tank, EFI fuel tank, or modified original tank, you’re typically left with a clean set of fittings that run out to the regulator, return to the tank, and a vent. No need to worry about mounting an external pump, then adapting plumbing to the original tank, then the pump as well as the filter and regulator. Just be sure there’s room for those fittings under your floor or truck bed. The full-flow 90-degree fittings on our C10 were mighty close to the bed floor, but there’s still sufficient room for everything.

While mechanical pumps pull fuel out of the tank, electric pumps typically push fuel to the engine and therefore need to be mounted in a place where gravity will assist in feeding fuel to the pump. Electric pumps really don’t like being mounted above a tank and having to lift the fuel out. As such, external pumps are best mounted low in the car, below the tank. This is another advantage of an in-tank pump as the pump and pickup are always immersed in fuel. This is doubly advantageous as the internal location also protects the pump. In applications such as off-road or even autocross where errant cones can wreak havoc, an external pump exposed to elements and road hazards can make for a bad situation. Internal pumps eliminate the possibility of something physically damaging the pump.

To complete our installation, we used one of our Deluxe AN6 GM LS Swap Fuel Filter/Regulators. These are slick because they serve as the regulator and filter as well as providing a return, all in one clean self-contained package. We tied everything together with Earl’s Vapor Guard fittings and hose.

Ultimately, the best fuel pump for your application is going to depend on various factors like power level and intended use of the car. To learn more about mechanical and electric pumps, check out our fuel pump guide.