All sorted on the engine front. I have a spare NT16 sitting around. As long as I am allowed to use it in the ST series, thats what is going in. If I end up using the Savage, I will be taking the RB out and putting the original S25 back in. If I cant use the NT16 but till fancy racing the CEN, I am thinking about picking up a rear exhaust .12 specifically to use in racing. I will see how everything shapes up first though.