Motorized two stroke scooters used to be very popular. Look up “Go-Ped” scooters. 49cc two-stroke motors with a ton of aftermarket parts including tuned exhaust pipes. Easy to make them go over 50 mph. Electric scooters and e-bikes are popular and how the law is written they technically not motorized vehicles because the motors on them are technically under 50cc. Pretty funny.

nitro and turbo, quite a lot, but that requires a lot of cooling as well... best you could do is maybe 70km/h on the flat... you'd need a tuned exhaust, spoked wheels, minimalistic frame to cut weight and decrease inertia