I know an aluminum underdrive crank pulley will be lighter weight then stock, 1.3 lb vs 3.6 lb and the smaller size will help reduce accessory drag.
I know this will not only free up some hp but also give you mpg gains as well.
Given that at 50 mph I get about 50 mpg would you guess are we talking a miniscule mpg increase of 0.5 - 1.0 mpg or something more around 1.5 - 2.5 mpg gained?
Here is the part...
5 ribs - Ecotec Underdrive Crank Pulley - 2.0LNF/2.2/2.4: by Make and Model - Chevrolet - Cobalt - NA Ecotec UDP - Car Performance Parts And Auto Accessories | MRZ Performance
I know I'm talking several years before breaking even but was just curious.