I've run the 2 speed in my truck. I couldn't agree more with rcnz, if you are looking to upgrade to a .18 motor GET THE OS .18 CV-RX. It is a WAY better motor than the 18ss motor. If you get the OS motor it would beat an MT with a T15 motor and 2 speed tranny easily.

I ran the 2 speed in my truck with my OS motor and it was crazy. Lots of low end and lots of top end. Fun truck to drive. Problem is, the 2 speed tranny does not have a slipper setup so your drive train is completely locked in when your clutch shoes are spinning the clutchbell so when you land off a jump with your motor revved you will be breaking parts or stripping spur gears.

If you are planning on running onroad and that is it, then the 2 speed would be fun to play with. If you are going to drive off road at all, stick with the single speed. Either way you go, get the OS .18 CV-RX, you won't be sorry!

Here is the 2 speed I used

http://cgi.ebay.com/HPI-2-Speed-Tran...QQcmdZViewItem

Here is the clutch bell I used.

http://www2.towerhobbies.com/cgi-bin...?&I=LXM729&P=7

and you would need this pilot shaft to run it

http://www2.towerhobbies.com/cgi-bin...?&I=LXM721&P=M

and run this racing clutch. It's awesome.

http://www2.towerhobbies.com/cgi-bin...?&I=LXLW03&P=M