I have to agree with
Rev, DynoSim is the shizzit, but you pay for it....unless you d/L it.
Desktop Dyno 2000 is pretty fun to use, so long as you don't give it every detail of the engine and then take the HP/TQ numbers as hard fact. We'll leave that to the ricers.
Its most useful feature is seeing how different combinations will move the torque curve around, and can give you a good starting point for future modifications. Makes you think twice before bolting a tunnel ram on a street car!