[dcb]

Hmm, lots of things have worked on different cars.

Best one by in my experience was swapping out an auto trans for a manual one. Cost about $500 (parts car w/stick + misc) and a very long weekend, but took it from 25mpg to a 50mpg in-town hypermiler, with appropriate techniques.

Of course you can get similar results with an auto, I think Gerdes does, I just felt more confident with a bump start backup for my starter, especially when the starter starts turning over slow. And the accelerating won't have the converter slip with a clutch.