Your most effective FE inspired modification

[GasSavers_JoeBob]

Rode a Triumph 650...over 60 mpg, and over 100mph (probably not at the same time...)

[i-DSi]

Until now: changed oil to 0W20 (came probably from 10W40) in the black one.
Compared to grill block this was a remarkable step forward. But I expect more from engine block heater I ordered for my car (the black one). My wife's car (orange one) has EBH since last Sunday.