LS Fuel Injector Guide – Lengths, Adapters & Spacers

Running the wrong fuel injectors in your LS engine can cause serious fitment issues — and even break parts. If your injectors don’t match the intake and fuel rail height, the rail can bottom out or leak. This guide shows you how to identify your injector height, choose the correct ICT Billet fuel injector spacer, and understand how different LS combinations work together.

Injector Length and Measurement

Each LS-style injector has a unique overall length. The correct way to measure them is from the center of the top O-ring groove to the center of the bottom O-ring groove. This determines how far your fuel rail will sit above the intake. A longer injector pushes the rail higher; a shorter injector pulls it closer to the intake.

• LS3: (shortest injector) – about 1.5 inches center to center
• Truck: (slightly longer) – about 1.8 inches center to center
• LS2: (medium length) – about 2.1 inches center to center
• LS1: (longest) – about 2.5 inches center to center

Always measure your injectors before ordering. GM changed designs throughout production years, so height can vary even with the same RPO code.

Injector Height → Intake Manifold → ICT Part #

Note – injector height can vary by production year. Always measure your injector height before ordering.

Injector Height Styles & RPO Codes Covered

LS1 Height: LS1, LS6

LS2 Height: LS2, L59, LMG

LS3 Height: LS3, LS4, LS7, LS9, LSA, L76, L77, L94, L99, L9H

Truck Height: L20, L33, L92, L96, L98, LC8, LC9, LFA, LH6, LH8, LM2, LM7, LQ4, LQ9, LR4, LY2, LY5, LY6, LZ1

Why Injector Spacers Are Needed

The most common reason to need an injector spacer is when your injector height doesn’t match your intake manifold. For example, if you install an LS1 injector into a 6.0L truck (LQ9) intake, you’ll see a large gap between the injector and fuel rail. That gap must be filled or you risk fuel leaks or broken parts. The same problem occurs in reverse when using a short LS3 injector in a tall truck intake.

ICT Billet spacers correct this by adjusting the rail height to perfectly match the injector. They also allow you to use different injector brands, sizes, and flow rates while keeping your fuel system sealed and aligned.

O-Rings, Spacers, and Bore Sizes

LS injector bores are typically 0.551”, but some LS2 and LS3 manifolds use 0.587” bores. ICT Billet injector adapters include both large and small O-rings to ensure proper sealing regardless of intake size.

The upper O-ring is the same across all LS injectors — only the lower size changes. Each kit also includes spacers to raise the fuel rail when needed, depending on the adapter length.

Dummy Injectors

Dummy injectors are used to block unused injector holes in dual-fuel systems. They match LS1 injector height and keep the fuel rail sealed and mounted, perfect for staged or twin-fuel setups.

Connector Styles

LS injectors use different electrical connectors depending on model:

• Truck / EV1: Common on most factory LS truck engines.
• USCAR / EV6: Used on LS3, LSA, and many newer injectors (GM & Ford).
• CNG / Nippon Denso: Found on 210 lb CNG injectors — short body, high flow, different plug.

ICT Billet offers wiring adapters to connect any of these styles to your existing harness.

Removing Intake Caps

Some truck intakes include small plastic caps in the injector bores that can prevent injectors from seating fully. These can be removed with channel locks or diagonal cutters if the rail sits too high or injectors don’t align.

Final Thoughts

Whether you’re running LS1, LS2, LS3, or truck injectors — ICT Billet makes adapters, spacers, and wiring harnesses to make any combination fit. All components are precision-machined from billet aluminum and Made in the USA. If you’re unsure what you have, check our visual guides or give us a call — we’re happy to help you Max Your Swap.