Well, there are two types of flowmasters. Original, and delta flow. I'm gonna say you have the delta flow, it's designed to have less interior noise. I got a Delta flow, with 2 1/4 pipe on a 1990 4 cyl Toyota, and it sounds nice. I can't believe that you can't hear it though. But there are certain things you can do to the pipe to make it sound louder. If you end the pipe right after the muffler, and have it face down (towards the ground) it will be A LOT louder than making it exit to the side. On our '90, it exits the driver side, and at a diagonal towards the ground so it's a little louder.
On my '04, I have the original series, exiting straight out the side, and it's perfect for me. Easy to hear even with the windows up, but not so loud it get's old fast.