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The LS3 intake manifold is a masterpiece of OEM engineering. It flows incredibly well, and for many street-driven builds, there is no reason to replace it with a heavy metal plenum or a high-rise manifold.
However, as you start pushing past the 400rwkw mark, especially if you're switching to E85, the factory injectors become a bottleneck. The challenge with the LS3 manifold is its compact design. Space is tight under the fuel rail, and if you buy the wrong injectors, the rail won't bolt down, or the injectors won't seal. Here is what you need to know about "shorty" injector fitment.
1. The Magic Number: 34mm (O-Ring to O-Ring)
Standard LS1 injectors are "long" (60mm). LS2 injectors are "medium" (53mm). But the LS3 and LSA use the "Short" or "Compact" style injector.
- Physical Length: ~34mm to 38mm (between O-rings).
- Why it matters: The LS3 fuel rail is positioned very close to the manifold. If you attempt to use a standard-length aftermarket injector, it physically won't fit without using fuel rail spacers. Spacers can cause the fuel rail to sit too high, potentially hitting the hood or interfering with the plastic engine covers.
2. The USCAR (EV6) Connector
The LS3 harness uses the USCAR (often called EV6) electrical connector. This is a square-shaped, push-to-click plug.
- The Good News: Most modern high-performance injectors (like the Excess Injector range) use this exact connector.
- The Trap: Some "budget" injectors still use the older, wider EV1 (Jetronic) plug. To make these work, you have to use "hat-style" adapters or cut your factory loom, both of which add bulk and potential points of failure.
3. Lower O-Ring Diameter: The Seal is Critical
One of the most overlooked parts of an LS3 upgrade is the lower O-ring. The LS3 intake manifold bore is slightly larger than the earlier LS1 manifolds.
- LS3 Manifold Bore: ~14.5mm to 15mm.
- The Fix: When upgrading, you must ensure your new injectors are fitted with the correct thick lower O-rings (usually red or blue in color). If you use a standard 14mm O-ring, you will have a massive vacuum leak, causing the car to idle poorly and run dangerously lean.
4. Top Upgrades That Fit Like Factory
At Excess Injectors, we’ve designed our LS3-specific kits to be a 100% "drop-in" solution. No spacers, no wiring adapters, and no guesswork.
- The 710cc injector Kit: Perfect for cammed LS3s on pump gas. It fits perfectly under the stock rail and provides enough fuel for up to 450rwkw.
- The 1100cc injector Kit: The go-to choice for LSA supercharged engines or LS3s running E85. This is the largest "short" injector that maintains excellent low-speed driveability.
- The 1500cc injector Kit: For those chasing serious power (600rwkw+) while keeping the stock intake.
5. What About LSA Superchargers?
If you are running the factory LSA supercharger (found in the HSV GTS or ZL1 Camaro), the fitment requirements are the same as the LS3. However, because the injectors sit in the supercharger housing, they are subject to extreme heat. This is why we recommend injectors with stainless steel internals and Viton seals for all LSA applications to prevent fuel leaks and sticking.
You don't need to sacrifice your factory LS3 intake manifold to get the fuel you need. By choosing a "short" style injector (34-38mm) with a USCAR connector and the correct LS3-specific O-rings, you can upgrade your fuel system in under an hour.
With Excess Injectors, you also get the Exact Match Data, meaning your tuner won't have to spend hours trying to make "big injectors" behave like the stock ones.