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.
Fuel-It! Bluetooth Dongle
https://fuel-it.com/products/fuel-it-bluetooth-flex-fuel-analyzer
ACDelco 13577429 GM/Continental Flex Fuel Sensor - https://amzn.to/3moc6H5
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E85 is a blend of 85% ethanol and 15% gasoline. Ethanol is very high octane and is ideal for use in high performance engines. The high ethanol content reduces the risk of knock and allows for higher compression ratios and more boost. However, you're never sure that you really got 85% ethanol at the pump. There is some risk that you might get ethanol content that is way too low or way too high for your tune or fuel system capability. It is essential to measure the ethanol content of E85 before using it in a high performance engine. Doing so will ensure that the engine is able to achieve its full potential and avoid damage from knock or fuel starvation when accelerating.
The Fuel-It! flex fuel analyzer is a plug and play device that attaches to a flex fuel sensor mated to your car's fuel line. It receives the composition of your fuel from the sensor and sends the data to your phone via Bluetooth. The app, which is available for iPhone and Android, then analyzes the data and provides you with information about the percentage of ethanol in your fuel. It supports GM and Continental ethanol sensors and will show you changes in the fuel blend that occur after refueling. This is one of the easiest kits you can choose for your vehicle and a very simple installation on the B9 Audi S4/A4.