From another thread: For those who are serious, this zeitronix is the gauge to have, showing real-time E85 content. I have posted the picture below in another thread, below from my STi: United I have found to be extremely reliable, with variation between 85 and 87% Eventually hopefully someone will produce an ecu upgrade that will support a full eFlex, for the Ford, without the need for multiple map switching and near tank draining. GMH have a full factory supported version. With my STi, the Vipec V88 ecu that I use can support a full eFlex, although I stay on 85. Ecutek produce an ecu flash where a R35 can use e85 in eFlex mode without map switching, and Ecutek is moving towards supporting other vehicles. I filled up with BP Ultimate 2 days ago, and it was $1.75c/L. E85 was $1.18c/L last week With these relative prices E85 looks good. However, when 98 is $1.60 and E85 is $1.35 it is around the other way. A full eFlex would be the best, so you choose based on relative price, or just stay with eFlex fuel (Caltex) or E85 if you want the extra power. Brian