yep you can put an 18 in it, i have one in mine, if its the RTR EVO version you will need mounts though, here is what i recommend

http://www2.towerhobbies.com/cgi-bin...&I=LXGGP6&P=ML
http://www2.towerhobbies.com/cgi-bin...?&I=LXCLR3&P=7
or the crappy mounts http://www2.towerhobbies.com/cgi-bin...&I=LXN373&P=ML
http://www2.towerhobbies.com/cgi-bin...?&I=LXDHM2&P=7
http://www2.towerhobbies.com/cgi-bin...?&I=LXDHM5&P=7
http://www2.towerhobbies.com/cgi-bin...?&I=LXCLR7&P=7
http://www2.towerhobbies.com/cgi-bin...?&I=LXM617&P=7
and if you dont already have it http://www2.towerhobbies.com/cgi-bin...?&I=LXLST3&P=7
and for the slide carb setup http://www2.towerhobbies.com/cgi-bin...?&I=LXCXF8&P=7 i ahve this same setup in my car and it hauls *****, my OS is highly modded and its insane, i currently have poweredbynitross sending me his os 18 cv-rx to modifiy