Well, they way I'm understanding this there are two sides to this and they are both valid.
A. It is physically possible for a bicycle to achieve speeds in excess of 80 mph.
B. Nobody has went 80 mph on a motorized bicycle, under the power of strictly the motor. Current engine designs just don't have the capability.
Is is likely, no.
Is it possible, yes.
If there was a joint project between the CIA and NASA with a secret budget to build an 80 mph motorized bicycle......
OP came here asking some questions and he got a variety of answers, and that's good. That's what this is for. I'm not going to be the one that discourages.
Never let reality get in the way of your dreams