our engine is completely different from the early aveo.

that cai looks like it will still work though. althoug i was going to try this one:

http://cgi.ebay.com/ebaymotors/96-00-Ho ... 240%3A1318

i figure you will need to cut the pipe that goes to the throttle body down, and then use a piece from the other section to get it into the wheel well..

they do make a cai for the aveo on ebay too. but from what i can tell our throttle body sits at a different angle. which may or may not matter..

the exhaust is best at 2" if you free up restriction, we dont have the other things available to need a bigger exhaust than that.

tires people are running up to a 18 inch wheel. not many, the popular choice is a 17 here.. your question about the two tires sizes is the wider footprint of the tire for better traction and handling. while maintaining most of the same sidewall height.

fuel economy and performance don't really going together all the time. but do influence each other a great deal.
right now, getting a light weight wheel tire combination (lighter than stock), a cai and freeing up some exhaust will give you some "power" and economy. Xiogary sells some parts on ebay to free up some more power (lightweight pulleys etc) and you can also do other machine work not jst engine internals to fee up more power (lighten the flywheel) so options are available, but nothing is buy and bolt on like a honda.