Flex fuel is(IMO) more of a marketing gimmick for claiming green status or alternate fuel vehicle status for emissions and CAFE reasons than a physical vehicle change. Modern EFI vehicles will handle flex fuel with slightly bigger injectors(which cost exactly the same as normal injectors when ordered in OEM qty's) and a software change. Therefor it's not always advertised, and you may have a vehicle that'll handle E85 already. Could be worth checking owner's manuals.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap