If you only want to do 100mph? almost any .60 two stroke nitro with tuned pipe or tuned muffler will do that. If you get it set up right and the right prop. Even though I am no OS fan, if you are new to the speed thrill, get an os .55 ax and the evolution tuned muffler, $60 or the jett tuned muffler. apc 11x7 for break in then try apc 10x8. 10% nitro and depending on what P51 you got you may get as much as 115 mph. the trouble starts when you want to get over 120+ Check out the Rossi .61 speed 13. great price, There are many engine choices but the supertigre is in my opinion not the ones to mess with. Unless it is some older rear exhaust pylon motos from the old days when two stroke nitro was in it's prime time. Good luck