I recently acquired a Schwinn S350 and immediately upgraded it to 36V.
Here's some things that I have the parts available for but wonder if they are worth trying.
1) Replace the S350's motor with a 500W motor from a broken Scwhinn Tsunami.
2) Replace the S350's speed controller with the controller from a broken Stealth.
3) Run the S350 at 48V
4) Replace the S350's front end with the front end of the Tsunami. The S350 has no shocks and no front brake. The Tsunami does have shocks and front brakes.
Would appreciate your comments.