Wheelpantz,
Both myself and m.gramling are flying our UCDs with the ST 90, and both of us are currently experimenting to find the best mousse can pipe setup for a ST 90 on a UCD. (go to this thread for more details about the MCP)
http://www.rcuniverse.com/showthread...435&forumid=21
The purpose of using a MCP is to get more power with less weight instead of using a bigger and heavier engine. So far, my ST 90 w/mcp is spinning an APC 15x4w at 11,400. This is about 1000 rpm faster than the stock muffler, and the throttle transistion and response are improved over the stock muffler too. Overall, I've been extremely pleased with my UCD!!