My truck is an '04 flex fuel. I currently have a 93 tune for cam/bolt ons/etc. if I wanted to run e85 will I have to make changes in the tune for best power? Also do I need to adjust for different percentages of ethanol content?

 

Yes, you always need to calibrate the ECM to optimize power.
If you have a flex fuel sensor and it is connected to the ECM then the ECM will adjust fuel and ignition timing according to the ethanol content measured in your fuel. So you do not have to change the tune based on different percentages of ethanol, but you should adjust the tune as necessary for maximum power.

 

Excellent, I'll fill up with corn and head to the tuner