Select Your Vehicle:
Browse & shop Flex Fuel Kits for your car or truck.
Flex fuel kits allow a vehicle to safely run multiple ethanol blends by automatically adjusting engine parameters based on fuel content. By monitoring ethanol levels in real time, these systems enable optimized performance, consistency, and reliability when switching between pump gas and ethanol blends.
Flex fuel setups are commonly used on Subaru WRX and STI platforms to support increased power, improved knock resistance, and greater tuning flexibility. When paired with proper fueling components and engine management, flex fuel systems provide a versatile solution for performance-focused builds.
Flex Fuel Kits for Subaru WRX and STI
Flex fuel kits for the Subaru WRX and STI measure ethanol content and communicate with the ECU to adjust fueling and timing in real time. This allows the engine to safely take advantage of higher-octane ethanol blends while maintaining reliable operation across varying fuel compositions.
Running E85 or a blended ethanol mix on a properly set up WRX or STI can support higher boost levels, reduced knock sensitivity, and more aggressive tuning compared to pump gas alone. For a full breakdown of what changes when switching to ethanol, our guide on E85 vs pump gas on WRX and STI covers the differences and whether the switch makes sense for your build.
We carry flex fuel kits from COBB Tuning, covering WRX models from 2011 through 2021 and STI models from 2008 through 2021. These systems are designed to integrate directly with the COBB Accessport ecosystem for seamless ethanol-based tuning.
For a broader look at how fueling upgrades work together on the WRX platform, our WRX fuel system upgrades guide covers the full fueling picture including flex fuel, injectors, and fuel pumps.
What to Consider Before Installing a Flex Fuel Kit
A flex fuel kit on its own does not add power. It enables the tuning system to safely adjust for ethanol content, which then allows more aggressive calibration when running higher ethanol blends. Professional tuning is required to fully realize the performance benefits of a flex fuel setup.
Most WRX and STI flex fuel builds also require supporting fueling upgrades to handle the increased fuel volume demand of E85. Our guide on fuel pumps vs injectors for WRX and STI explains which component becomes the limiting factor first and when each upgrade becomes necessary.
For the 2022 and newer WRX on the FA24 platform, the COBB CAN Flex Fuel Upgrade is the current solution. Browse the full COBB Tuning lineup for all compatible flex fuel and fueling accessories.
Related Fuel System Upgrades
- Fuel Pumps commonly upgraded alongside flex fuel kits to support increased fuel volume demand on E85.
- Fuel Injectors higher-capacity injectors often required for higher ethanol blends and power targets.
- Fuel Rails matched fuel rails support consistent fuel delivery across all injectors.
- EFI Tuning professional tuning is required to calibrate the flex fuel system for safe and optimal performance.
- WRX Fuel System Upgrades Guide plan the complete fueling upgrade path for your WRX or STI build.
Don't See Parts for your Vehicle?
We'll find it for you within 24 hours! Click the parts locator below: