glasspacks will quieten em down a little. I drove my 91' around for a day or 2 without anything but pipe on it (was gettin work done in 2 days) and it was not loud at all.

 

Depends a lot on the type of glass pack. There are two types, louverd and non-louverd. Louverd GP's can cut down sound a lot unless they're mounted backward, non louverd do almost nothing.

My DD in college was a 70 Impala Wagon with 300hp motor (at the wheels) with nothing but a 3" glass pack about 30" long. This was when I still lived in Los Angeles too. LOL