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2018-2021 Subaru WRX STi 2.5L E85 Flex Fuel Conversion Kits

Boost your HP by up to 20% With our Plug-and-Play E85 Kits

In 2015, Subaru decided to focus their Rally Car efforts on the WRX STi sedan and we are here for it. The 4th and current generation of WRX STi still gets its speed from the 2.5L turbocharged 4-cylinder, capable of 310 horsepower but its suspension got a major overhaul. Reminiscent of the 2000-2007 Impreza WRX STi, the current generation has a much tighter turn with quicker steering and super sharp reflexes for sailing through the curves. Boost the horsepower by up to 20% with one of our WRX STi E85 flex fuel conversion kits and you have a real track contender.

No tuning required!

$699 List price $874

Starting at $61.50 / month with Affirm logo

Truspilot consumer rating 4.7 SKU: U-EF-PLUS
  • Free shipping
  • Delivery time 2-5 days
  • 5 year warranty with registration


The eFlexPlus and the eFlexPro are so easy to install that you can do it yourself in an afternoon and have your car running any mixture of E85 flex-fuel and standard gasoline the same day. Both come with a handy phone app that allows you to monitor the fuel mixture and switch between efficiency and performance profiles, effortlessly. The eFlexPro comes with the additional eFlexTuning software that allows you to tune your turbocharged engine on any mixture of fuel above E50. Order one of these for your 4th generation Subaru WRX STi today and increase your horsepower by up to 20%. Your HP can go from 310 to 370 ponies. That’s not bad for a couple of hours of “work”.


DIY level

Plug&Play installation with some modifications - An experienced mechanic will install in 2-3h. For first time DIY installation, expect to double the time needed.

Technical specs

Make & ModelSubaru WRX
Engine2.5l / EJ257
Power310 hp
Fully Automatic Flex FuelAlways Optimized Fully Automatic Flex Fuel
Cooler & Cleaner EngineCooler & Cleaner Engine
No Tuning NeededComplete System, No Tuning Needed
Increase PerformanceUp to 20% Increase in Performance
Flex Fuel System VerifiedYour Fuel System Verified
Dynamically adjust engine tune to match fuel
Available performance and eco tunes
Select performance or eco tunes via eFlexApp
Create and save custom dyno tunes
Pro grade eFlexTuner tuning software

+ What's included

+ eFlexApp

+ eFlexTuner

+ Installation

+ Returns

+ Warranty

What's included in the eFlexPro E85 flex fuel conversion kit / Installation

Note: If your car is modified you can use E85 with eFlexFuel. If this is the case, please list all the main engine modifications on the checkout page. Our technical team will ensure that your setup is fit for E85.

* Power and torque increase depends on your engine technology and/or your custom built of the engine.

Prop 65 Warning
Warning signNot legal for sale or use on pollution-controlled vehicles

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