LS and LT Swap Fuel System Guide

Fuel system questions come up on almost every swap we help with. The good news is it's straightforward once you understand how it works.

Here's what we recommend based on hundreds of LS and LT swaps.

How Return Style Fuel Systems Work

Most LS swaps use a return style fuel system, and it's worth understanding what's actually happening.

The pump flows way more fuel than the engine needs. All the time. At idle, at cruise, at wide open throttle. The pump just keeps pushing fuel.

The regulator sits at the fuel rail and holds pressure steady, typically 58 PSI for LS applications. Whatever fuel the injectors aren't using at that moment gets bled off through the return port and sent back to the tank. At idle, most of the fuel returns.

At wide open throttle, less returns because the injectors are spraying more. But fuel is always flowing through the system and always returning to the tank.

This constant flow does two things. It keeps pressure rock steady at the rail no matter what the engine is doing. And it keeps the pump cool because fuel is always cycling through.

In-tank pumps rely on that fuel flow for cooling. A pump that's just sitting there not flowing will overheat and die early.

LS Swap Fuel System Setup

For a basic LS swap, here's what we recommend.

The Tank

You need an EFI tank with a baffle inside. The baffle keeps fuel from sloshing away from the pickup during acceleration, turning, and braking.

Without it, you'll starve the pump when the tank gets low. Tanks Inc sells complete setups that drop right in for most applications.

The Pump

A 255lph pump handles most builds. Walbro and Aeromotive are the common aftermarket choices. For squarebody trucks, the ACDelco EP381 is an OE option that works well. Whatever pump you use, in-tank is the way to go. Quieter, cooler, more reliable than frame mounted.

The Regulator

A Corvette fuel pressure regulator is perfect for LS swaps. Return style with a -6AN return port. Mount it as close to the fuel rail as possible. This helps prevent vapor lock, which can still happen on an LS when underhood temps get high.

The shorter the path from rail to regulator, the better.

Lines and Fittings

We use Gates Barricade hose with push lock fittings. Some builders add a hose clamp for extra security. Run 6AN for the feed and return. We sell all the fittings and hose on the website.

That's the whole system. Tank with baffle, pump, feed line to the rail, regulator at the rail, return line back to the tank. Fuel flows constantly, pressure stays steady, engine runs right.

Returnless Systems

Some factory trucks came with returnless setups where the regulator is built into the tank or fuel pump module. The Holley drop-in modules work this way too.

Most LS swaps we see go return style because you can adjust pressure at the rail and it's easier to diagnose if something acts up. But returnless can work if you're using a complete drop-in module designed for it.

Gen V LT Fuel Systems

LT engines run different than LS. Factory Gen V applications use a pulse width modulated fuel pump. The ECM controls pump speed based on demand. Higher pressure too, because direct injection needs it.

That means more wiring, a PWM compatible pump, and a more expensive tank setup if you try to replicate factory.

But here's the thing. You don't have to run PWM.

We've set up plenty of LT swaps using a traditional constant-voltage fuel system. One of our techs runs an LT4 in his Chevelle this way. No PWM controller, no expensive tank, just a solid fuel system that works.

The Pump

The Tanks Inc Hellcat pump flows enough for LT applications and runs on constant voltage. No PWM signal needed.

The Regulator

An adjustable regulator works in place of the factory PWM system. LT engines run higher fuel pressure than LS because of direct injection. The exact pressure depends on the application and tune, so an adjustable regulator lets you set it where the engine needs it. We won't give a specific number because every setup is different.

The Lines

For higher pressure LT applications, braided fuel line with the rubber coating handles the pressure well and looks clean. We can get this for you.

The Harness

We build harnesses for LT swaps that work with a traditional fuel system instead of PWM. That's what makes this whole approach possible without hacking factory wiring or buying expensive controllers.

The point is you can skip the PWM complexity and run a traditional setup with the right pump, adjustable regulator, and harness. Works great on multiple builds we've seen.

What We Sell

We carry everything for the fuel system. Tanks Inc kits, pumps, regulators, fittings, hose, all of it. If you're not sure what your application needs, give us a call. We'll walk through your setup and make sure you get the right parts the first time.

Bottom Line

LS fuel systems are simple. Good pump, Corvette regulator at the rail, return style plumbing, quality hose and fittings. Fuel flows, pressure holds, engine runs.

LT fuel systems don't have to be complicated either. Skip the factory PWM setup and run traditional with the right pump, adjustable regulator, and a harness that supports it.

Get the fuel system right and it's one less thing to troubleshoot on startup day.