Welcome to the forum! Here's a little info- 2-stroke engines are usually faster than 4-strokes, and there's a lot of performance parts available for 2-strokes. 4-strokes usually have more torque and low-end power, also more expensive. 4-strokes don't sound as much like a dirt bike. bikeberry.com has a large selection of engines and bike parts. sickbikeparts.com has all the performance parts (i think all for 2-stroke engines) like shift kits and expansion exhaust pipes, for more power. Cruiser-style bikes usually work the best, or bikes with a LOT of space in the middle, and normal size frame tubes(not oversize tubes). Usually older bikes. If the bikes shifts, you won't have to worry about modifying the brake arm that one-speeds usually have. Most people like the Cruiser bikes.