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Flex Fuel is the ultimate "have your cake and eat it too" modification. By adding a sensor to your fuel line, your ECU can automatically adjust boost, ignition timing, and fueling based on the ethanol content in your tank.
However, a Flex Fuel setup puts a unique strain on your injectors. They need to be small enough to provide a perfect idle on pump gas, yet large enough to flow the 30% extra volume required by E85. They also need to be chemically resistant to the corrosive nature of ethanol.
Here are the top 5 injector choices for a reliable, high-performing Flex Fuel setup.
1. The All-Rounder: 1100cc (105 lb/hr)
This is the "Goldilocks" of the performance world.
- Why it’s great for Flex Fuel:1100cc is large enough to support roughly 500–600hp on E85 (depending on the engine), yet it is small enough that modern ECUs can still maintain a rock-solid idle on standard pump gas.
- Best for: Turbo 4-cylinders (SR20, K24) and moderately boosted V8s (LS, Coyote).
- The Excess Advantage: Our 1100cc units feature stainless internals, making them immune to the "internal rot" common in Flex Fuel cars that sit for a while.
2. The Street King: 710cc (68 lb/hr)
If you aren't chasing four-digit horsepower, bigger isn't always better.
- Why it’s great for Flex Fuel: On a naturally aspirated build or a low-boost street car, a 710cc injector provides incredible "resolution." This means the tuner has more precision at low RPMs, leading to better fuel economy and smoother throttle transitions when switching between fuels.
- Best for: Cammed LS engines, NA Barra builds, and GTIs.
3. The Powerhouse: 1500cc (142 lb/hr)
When 1100cc isn't enough, but you aren't ready for a dedicated race injector, the 1500cc is the answer.
- Why it’s great for Flex Fuel: It bridges the gap for high-boost applications. Because it uses a modern internal design, it avoids the "choppy" idle often associated with larger, older-style injectors.
- Best for: 800hp+ Barra builds, Twin-turbo LS setups, and high-boost 2JZs.
4. The High-Pressure Specialist: 1000cc (95 lb/hr)
Some fuel systems are designed to run at higher base pressures (50-60 psi) to get more out of a smaller injector.
- Why it’s great for Flex Fuel: Using a slightly smaller injector at higher pressure can sometimes improve the "atomization" (the fineness of the mist), which helps cold-starting on E85, one of the biggest complaints of Flex Fuel owners.
- Best for: Supercharged applications where manifold pressure is high.
5. The Maximum Flow: 2000cc (190 lb/hr)
This is the limit for a street-driven Flex Fuel car.
- Why it’s great for Flex Fuel: If you are chasing 1000hp+ on E85, you need the volume. While 2000cc injectors are huge, the latest generation of Excess Injectors can still be "tamed" for pump gas use, provided you have a high-end ECU (like Haltech or Motec) and Exact Match Data.
- Best for: Dedicated drag cars that still want to be driven to the local car meet.
Key Features to Look For
Regardless of the size you choose, your Flex Fuel injectors must have these three things:
- Stainless Steel Internals: To prevent corrosion from the ethanol/water mix.
- High Impedance: To stay compatible with modern ECUs without needing a resistor box.
- Detailed Latency Data: Because the "Dead Time" will feel different to the ECU when switching between the densities of Gasoline and E85.
Choosing injectors for Flex Fuel is a balancing act. You want enough flow for your "E85 Goal," but you don't want to go so large that the car becomes a nightmare to drive on 98-octane. For most enthusiasts, the 1100cc Excess Injector kit is the perfect starting point for a versatile, reliable build.