The next build

I am doing some research (web cruising) on the HS 49 cc motor for my next build. I find a 4G T belt drive motor and I find a stage 3 motor for almost the same price. The stage 3 has a pipe the 4 G doesn't. Is the difference in the drive (primary) or what? I do like the idea of the timing belt primary drive I don't like the idea of spending another $50.00 or so for a pipe. So what is the difference in the two? What is the exhaust on the 4 G like? The stage 3 and the 4 G look like the same motor with a different drive, am I right?