Hi, I've got a 2000 Tomos Sprint, and have just finished going through an upgrade.
I went with the speed kit and all, but before changing everything I tried out just the
new sprocket and the BiTurbo. The BiTurbo gave me about 5-7 more mph, and the
new sprocket gave me about another 5 mph. In total the combo will give you another 10 mph (your mileage may vary). That was in a sprint, I would think it might be a little more effective in a Targa. My top speed was 30 (33 with tailwind)
and after just the sprocket & BiTurbo, my needle sat right on the 40.
The sprocket will require a slight modification to the case. There is a reinforcing rib on the case in about the 9:00 position that needs to be ground down slightly to make room for the slightly larger diameter. If you''ve got a dremel too, it's a snap.
First you take off the case, and then, flaten down the one edge of a washer beneath the nut that is bent up to prevent the nut from moving. Removing the nut
is "lots" of fun. I had to go out and buy a bigger adjustable wrench, and then whack at it with a hammer to loosen the nut. My bike only had 100 miles on it so
you may not have such a hard time.
If you are not changing the cylinder, you can go with the 1 piece muffler, and it should just be a bolt up change. My kit came with a two piece. The clamp that is supposed to hold it together was a piece of cr@p, and it did not line up with the mount on the swing arm (too low). Luckily I have a friend at the local muffler shop who welded the pieces into one for me this weekend. It still sits about an inch below the hanging bracket in the back, but I just got a piece of steel to fit, drilled
two holes, and mounted it all together. My friend was afraid the welding needed to heat and bend the pipe would discolor and possibly peel the chrome. He loves the chrome/gold muffler on a moped :-)
With the BiTurbo in, you will want to change to a side kickstand. The old one will drag going around corners, cause the new muffler gets in the way of the kickstand coming all the way up.
I tried the sprocket before the BiTurbo, and I lost a little acceleration, enough to notice, but not enough to care. Once I had the muffler on though, my acceleration was much better than it was before changing the sprocket. If you do them both, you will be much better off, but I don't know about 50 mph