Back in the 1960s it wasn’t uncommon to see scores of muscle cars like Mustangs, Camaros, and the like lined up at the local exhaust shop to have a set of Thrush’s red Glasspack mufflers installed.

Inhale, exhale—breathing is as important for your engine as it is for the human body. But while we're stuck with the lungs nature gave us, mechanical things can be improved with the right selection of ...