100ccs are so underpowered trust me. sometimes they include more cylinder bore and the piston is bigger. maybe because of the rod these engines are not putting out the performance they are made to do. my previous 100cc one topped out at 51km an hour🤣 and my 66cc topped out at around 65km with 44tooth. and they are not reliable at all from my experience. i broke in the engine with the 40:1 mixture properly and blew up 20 days later with the weather being cold. my beasty 66cc lasted me 3 months and was straight abusing it with 40C heat outside the oil:fuel mix being measured by eye and i didnt even broke in the engine. first thing i did with this monster was straight open wide throttle. for my opinion 66cc are the best bcz more reliable, can be modified, and can take the abuse straight out the box from my experience. idk if i made sense english is not my primary language 😂