Can I put e87 instead of e85 on a flex fuel car, ethanol gas?



Flex fuel cars usually can use between E0, that is pure gasoline, to E80. E87 and E85 would be too much ethanol, unless your car is rated for up to E100 (100% ethanol). But I think you are confusing ethanol with octane. 87 R+M/2 is regular octane, specified for most vehicles. 85 is regular in high altitude states.