| they mention in add the bore is 1 3/4 inch which is 45 mm so i would say this kit is a 49cc with some port mods only, check out the price of a stock 49cc barrell / piston / rings / bearing and pin then compare the difference.
the best barrell mod for performance is the machined barrell / head kit, this has a separate head /dome ect which produces the best power for any air cooled. | 
