Ultimate OBS 1988-1998 Chevy & GM LS fuel system Swap Guide (2024)

This fuel system swap guide will show you all of the parts needed to successfully install an LS engine into your OBS (old body style) Chevy or GM pickup truck.

As the years pass by different generations of pickup trucks gain popularity, as original C10 trucks became harder to find guys started to build square body trucks and further along the popularity of the OBS Chevrolet and GM trucks has increased. With this increase in popularity builders have started to look at swapping LS motors into the trucks to gain the reliability and power only an LSx series engine can provide.

Advantages of LS swapping an OBS 1988 to 1988 K1500 or C1500

When comparing the parts and work needed in completing a fuel system for an OBS LS engine swap to other series of GM trucks like the squarebody or original series old body style owners have the advantage due to this truck platform being originally designed for EFI fuel injection with the TBI system.

This means that you are able to install a high pressure fuel pump directly into the factory sending unit and avoid having to replace fuel tanks. There are special adapters available that allow a direct conversion from the factory TBI fuel fittings to AN helping to keep the fuel system portion as simple as possible.

OBS TBI vortec to LS swap fuel system parts list

Here you will find a complete listing of all of the parts needed to successfully swap both return and return-less style LS engines into your old body style chevy or GM K1500 / C1500 truck.

Return-less style LS swap parts list for OBS (old body style) trucks

The first thing that needs to be upgraded when completing an LS swap for these trucks is the fuel pump. You have multiple options to choose from when upgrading the pump each with there own benefits.

Your first option for an LS swap or EFI conversion with a factory power level up to 450HP is the

Spectra Premium 190LPh Fuel Pump - HERE

For a bit higher flow and support up to 550HP the

Walbro 255LPH pump - Found HERE

If you are producing a bit of extra horsepower the Aeromotive 340LPH is another good option. Again this pump will fit in the factory sending unit. There are other considerations with this pump such as regulator and electrical connections.

Aeromotive stealth 340LPH fuel pump -Found HERE.

Adapter fittings to convert factory sending unit to AN6.

M16 x 1.5 to 6AN - Found HERE

M14 x 1.5 to 6AN - Found HERE

The Hot Rod fuel hose Return-Less LS swap kit, for a return-less system you will need 20ft of hose if mounting the corvette regulator/filter close to the tank. Longer lengths of braided AN PTFE hose are available if needed. You can chose both your hose and fitting colors with this kit.

Return-less LS swap kits by Hot Rod fuel hose - Found HERE

These parts are everything needed to complete this OBS LS engine install from a fuel line perspective. As always if you have any questions you can reach out to us on our Contact Us page.

Return Style LS swap parts list for OBS (old body style) trucks

The parts needed for converting a TBI OBS engine to an return style LS engine can be found below.

As before you will need to replace the factory fuel pump with a high pressure fuel pump. The most popular of which is the Walbro 255LPH in tank pump. This pump is compatible with the factory sending unit and will deliver the flow and pressure needed to supply the LS engine.

Walbro 255LPH pump - Found HERE

For higher horsepower applications the Aeromotive 340LPH continues to be another good option for return-style LS engines. This pump will fit in the factory sending unit.

Aeromotive stealth 340LPH fuel pump -Found HERE.

Adapter fittings to convert factory sending unit to AN6.

M16 x 1.5 to 6AN - Found HERE

M14 x 1.5 to 6AN - Found HERE

A fuel filter will be required in addition to the other parts with this kit, we have both factory style fuel filter options and aftermarket fuel filter options.

Factory style fuel filter with AN adapter fittings - Found HERE

Aeromotive 10 Micron fuel filter (requires 10 ORB to AN fittings) - Found HERE

Holley 10 Micron fuel filter (requires 8 ORB to AN fitttings) - Found HERE

Finally the Hot Rod fuel hose return style LS engine swap kit will complete the needed parts for your OBS 1988 to 1998 GM or Chevrolet LS swap. For a return style swap you will require a 30FT kit to be able to run both the feed and return to the factory fuel rails found on the LS engine.

Return style LS swap kit - Found HERE

Back to blog