the sound in mine was pretty noticeable, had 2 1/2" exhaust and it sounded like a ricer before, now it has a burly sound
propane runs clean. i think they don't want us driving around with it is because of no road tax. funny thing.. home made electric and veggie oil cars don't pay road tax. so if you invent anything, no matter how clean it is,or how much fuel your saving, your probably illegal.
I might be wrong, but when I was checking around I talked to some state worker at the DOT, here in Utah, that told me there was like a $150 fee or something for running propane, the guy was a jerk about it too
