That ad has been floating around here confusing new builders for a couple of years.
Like MBR said, don't fall for it.
The 80cc designation came about because someone, somewhere decided to add the combustion chamber volumn to the actual displacement of the engine. That isn't how total displacement, cubic centimeters, is calculated. The cylinder bore diameter and stroke of the piston are the only two measurements used to get displacement.
Many sellers use the 80cc claim in their ads so Internet search engines will group them when a person is looking for bicycle engine kits. Most of them have gotten away from this practice, or include a disclaimer, but there are still a lot who haven't hoping to fool new and inesperienced buyers. There are no true 80cc Chinese bicycle engines.
Tom