Just got an '83 Impala. 33k miles and has been tuned up. Runs well.

Just wondering if I should consider any upgrades that would increase performance some with minimal harm to mileage. Want to stay far away from the point of diminishing returns. Money isn't a big consideration, but I don't want to transform my car. Not yet at least. I've wanted a box for years and I like them for what they are. Maybe I'll try something more radical when I roll over the odometer.

Really, I guess I want to F with it just to F with it. Please be specific with any suggestion. My mechanic would be performing any work.

Thanks.