[MetroMPG]

On the topic of exhaust tuning, I'm no expert (I just play one on TV).

But this is what I've read from people who know more than I do: opening up your exhaust is what you do if you want to improve high RPM performance - something you're not going to be doing if you're driving for efficiency.

Doing that may hurt low RPM performance (torque).

For best MPG, you want low end torque, and for that a standard exhaust with stock "restriction" is best.