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How To Install A Holley In-Tank Retro-Fit Fuel Module Kit Into Your OEM Fuel Tank

Author: Ryan Manson | 12/21/2020 < Back to Motor Life Home
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Updating an original, vintage fuel tank to cooperate with a modern EFI system can be a challenging affair. The lack of extra ports in the tank for a return line or fuel tank vent, something most EFI systems require, has been problematic since the first carb was swapped out decades ago. The need for an increase in fuel pressure over the stock, mechanical fuel pumps of the time, meant adding an electric fuel pump somewhere between the tank and the engine, usually on the frame rail. This commonly resulted in a pump that ran loud, ran hot, and suffered from notoriously short and unreliable life spans. While the easiest solution (albeit an expensive one) was to simply toss that original tank and replace it with a new tank designed especially for an EFI setup, there is a different option available today that allows the use of a stock fuel tank while inheriting all the ideal requirements of a modern EFI system.


Modifying your original fuel tank to accept a modern EFI system's requirements is made simple using Holley's In-Tank Retro-Fit Fuel Module Kit. No welding, machining, or other tricky fabrication is required; installation consists of drilling a single hole anywhere on the fuel tank and the Module slides right inside your fuel tank. Holley's In-Tank Retro-Fit Fuel Module Kit puts a modern EFI fuel pump inside the fuel tank, which solves the aforementioned heat soak, noise, and reliability issues common with a frame-mounted pump while also providing plumbing solutions that include an outlet, return, and vent lines. This single, modular unit also features Holley's innovative HydraMat fuel pickup design to deliver fuel reliably during any driving scenario.


Holley's In-Tank Retro-Fit Fuel Module Kit converts that original fuel tank to a true, modern EFI-compatible system and it does it easily and reliably.


Holley In-Tank Retro-Fit Fuel Module Kit pump hangar assembly

Holley's In-Tank Retro-Fit Fuel Module Kit consists of three major components. The first component is the fuel pump hanger assembly, which contains the inlet, outlet, and vent line fittings and also serves as the foundation for mounting the fuel pump. Its modular design keeps things streamlined so that the assembly fits where space is at a premium, while its innovative clamping system allows the unit to rotate 360-degrees for flexible plumbing and wiring routing options.

Retro-Fit Module fuel pump

The fuel pump attaches to the fuel pump hanger assembly via a pair of clamps by using a billet bracket designed to control pump vibration while also providing a low profile design. Holley offers Retro-Fit fuel modules with a 255LPH pump, 340LPH pump, 450LPH pump, and a 525LPH pump, the larger of which is good to support 1,200 horsepower on EFI or 1,450 horsepower with a carburetor.

Retro-Fit Module HydraMat

The third component and one of the items that makes the Retro-Fit Fuel Module Kit so unique is Holley's proprietary fuel pickup design called HydraMat. Race proven on the track and on the street, Holley's HydraMat fuel reservoir system is designed to maintain adequate fueling during the most aggressive starting, stopping, and hard cornering. Surface tension and fluid wicking are the secrets of the HydraMat’s ability to draw fuel from nearly any area that has contact with fuel and store it in the internal reservoir, eliminating the need for special pickups or internal baffling to provide adequate fuel delivery in any circumstance. Available in a myriad of sizes, the HydraMat that comes as standard with the Retro-Fit Fuel Module is 3x15-inches and features six clocking pin locations to allow for 360-degree adjustment to clear fuel level sending units or any tank floor restrictions.

Retro-Fit Module Cutting A Hole

The first step to installing the fuel module is to choose a location on your gas tank that's going to have the least amount of interference. Internal baffling and fuel level senders need to be avoided for best results. Clearance between the floor of the vehicle and the fuel tank should also be taken into consideration due to the pump hanger assembly's thickness (1.275-inches). Once the location is chosen, a 3 1/4-inch hole will need to be cut into the tank using a hole-saw.

Retro-Fit Module tank measurement

Once the hole is cut, the depth of the tank is measured, noted, and compared with a set of specifications provided by Holley. While our tank is relatively shallow, the Retro-Fit Fuel Module is compatible with tank depths from 7 1/2 to 12-inches, fitting a large variety of applications

Retro-Fit Module measure to fit

These specs will determine the amount of material to be removed from the fuel pump inlet...

Retro-Fit Module measure to fit 2

...as well as the billet fuel pump mounting bracket.

Retro-Fit Module fuel pump bracket installation

Once the billet fuel pump mounting bracket has been trimmed, it's installed on the fuel pump hanger assembly using two screws and lock washers. Here, the innovative mounting design is visible on the underside of the hanger assembly. As each screw is tightened, the aluminum lugs rotate into position and draw the assembly in tight to the top of the tank.

Retro-Fit Module fuel pump installation

Next, the fuel pump inlet hose is attached to the hanger assembly before the pump is snugly tightened to the fuel pump mounting bracket. The wiring connection is then made while being mindful not to pinch any of the wires in the assembly.

Retro-Fit Module HydraMat installation

The HydraMat snaps in place on the bottom of the fuel pump and can be easily removed and reinstalled. Its design allows it to be installed in six different orientations in order to help avoid any internal obstacles.


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