What are the differances between the DRZ motors?

Carburetor, cams and head gasket. You can increase the power with some small modifications (see first link to article), but to get equivalent power to the 400e you need at least the new carb and cams. The exhaust doesn't make much difference and I hear you may be able to fit the offroad 400e exhaust with some different connections at the head, and it works as well as expensive aftermarket stuff. I like the quiet stock exhaust.

The DRZ400s stayed the same engine wise through its entire model range, even the Sm version is the same, so nothing off a newer 400s/sm will help. The ADV rider pages in the answer above, 4strokes.com and Thumpertalk.com (links below) all have several pages, advice and guides on how to improve the bike.

Note the one improvement in the newer 400s, I think starting in 2003, is fully adjustable front suspension. My '04 has the better suspension, check the top of the forks on your 2002 to see if it has the adjusters.

I really like my 400s and ride on and off road, with legal knobbies (both Michelin and Dunlop make good legal off road tires). I agree its a bit top heavy off road only but strangely taking the mirrors off seems to help a lot (maybe it allows me to get forward). Like everyone else I didn't like the stock tires especially in sand, but full knobby tires are not the best road tires either. My tires are wearing so well I haven't had the chance to try dual purpose tires. Mine is stock except case and radiator guards, hand guards and an aluminum bar. I get easily over 60 mpg on road, and don't feel underpowered on a highway, but you notice how small the stock gas tank is during longer rides. When I decided to sell a bike recently it was not the 400s!

Good post on the differences:

http://www.advrider.com/forums/showthread.php?t=87...

I had an '04 DRz S. I killed it due to hard riding(hare scrambles and daily commuting) and lack of maintenance, but it was a fun bike. It's tall and heavy, but if you have the need for that much power then it's a good choice.

I scaled back to a KLX 250 S, and use it in Breckenridge, CO for climbing the big mountains in site-seeing mode. I'm a bigger guy 6' 220# and it goes without issue, even with my 5' 9" 150# GF on the back.(The 400 would probably be better with her on it, but I love it solo.)