Re: max size motor possible for in frame build
There's a million answers to your extremely vague and general question you have asked. Despite what details you posted.
No matter what, when you put an engine with over 2-3 HP on a bicycle, you are creating an illegal moped or motorcycle in the eyes of the law.
If you want more power, go buy a motorcycle. That's my opinion and I'm sticking to it.
When new guys show up here and immediately ask about large motors I fear for them.