Okay. I'm going to be getting a HPI firestorm soon. I want to upgrade the angine after I get it. I am thinking about either an OS .18. Which model do I need. (I need rotarary carb)TZ, CV-R (I dont know if thats right). Anyway. What model OS would be a direct drop in. I was also thinking about a Associated Z.18s Pro spec http://www3.towerhobbies.com/cgi-bin...?&I=LXPRL0&P=0 . Which engine is faster and whick is a direct drop in. Also, does anyone have a link to the OS .18 (whichever model is the direct drop in)( Preferably on tower). Also, what exhaust header would I need for the OS or for the Associated? I dont know if the stock on will fit?

Thanks so much guys