X85 is a cost effective E85 racing fuel blend. Unlike pump E85, X85 offers consistency from batch to batch. It is blended with 85% high quality ethanol and 15% premium racing fuel. What is the difference between X85 & C85? C85 will make more power than X85. C85 will also require re-tuning. X85 is a closer alternative to pump E85. It does not require re-tuning and can be tipped straight in.