I decided to convert my 2018 Audi S4 (B9) to E85 to boost performance. E85 is a high-octane fuel that can provide significant power gains in turbocharged engines. It is also very inexpensive, cheaper than 93 octane gasoline. The results of my E85 conversion have been impressive with 034 Motorsport's excellent E85 tune. My S4 has shown a big improvement in 1/4 mile runs and I'm down to just 3.46s accelerating 0-60! However, E85 ethanol content must be verified to ensure that your tune can support it. In my case I chose to use the Fuel-It! Flex Fuel analyzer paired with my iPhone.