Engine For TOPCAP
It the topcap a kit any good .46-53 will have more than enough power.
If it is a ARf, I would go with a YS63 or Saito 72.
I had a topcap ARf, with a YS63 and absolutely loved it. Put the YS63 on a Knife ARF and loved it. But my topcap ARf, and knife ARF on a 46 size 2 stroke just wasn't the same. I like 4 stroke on it better.
I have a knife kit that has a TT46 with stock muffler on it, and performance is great. I haven't had the urge to put the YS63 on it because I am happy with a kit and TT46.