How do you add E85 flex fuel capability to a non-flex-fuel LS truck?

Three parts: a sensor, a fuel system that keeps up, and a tune with flex logic.

• Sensor: a GM/Continental-style ethanol sensor inline in the fuel line (CPR Racing places it before the rail; some sensor makers design it for the return line). It's a three-wire sensor that sends ethanol content as a frequency, about 50 Hz at 0% to 150 Hz at 100%.
• Fuel flow: plan for 30–40% more fuel-system capacity (Performance Racing Industry). Keep injectors at or below 90% duty (some sources use 80%) and leave the pump 10–20% headroom.
• Pump: LSX Magazine's LS1 F-body conversion needed a high-flow, E85-compatible pump, because ethanol's low lubricity quickly wears out a standard pump.
• Materials: stainless-internal injectors (such as Bosch EV14), Viton O-rings, and a serviceable inlet filter on each injector. Avoid PVC, nitrile, natural rubber, urethane, non-anodized aluminum, zinc and brass (Performance Racing Industry).
• Tune: fuel for the 30–40% increase, adjust the cold-start tables, and only then add timing — E85's knock resistance allows more, but only once the calibration is made for it.
• Flex logic in the tune so fuel and timing follow the measured blend.

See fuel, E85 & boost.

Want to do it yourself? See who tunes it, and how to learn.