The 212 is capable of making that kind of hp peak. It will not make it at 5000rpm. This statement is coming from more then one go kart engine builder that I trust personally. It will make 21hp with the cam the OP posted it has. A good hard running gas stock appearing hemi predator with a welded head and some superior head work will make 21hp. Just not at 5000rpm. 7k+ yes. The OP doesn't state what head work is done, what the ports look like and what valve sizes are. If the ports aren't amazing and the head isn't welded it isn't making 21hp. I have a personal friend that is local to me with a dyno. We can make a 13hp Honda have 20hp. If you run the dyno correctly. Is it correct, no it isnt. Is it lies, certainly.