GOOFIT 44mm Big Bore 53cc 54cc Top End Kit for 2 Stroke 47cc 49cc Engine Mini Quad Pocket Bike Fit for 2 stroke 43cc 47cc 49cc 50cc engine(read description for more fitment infos) Performance upgrade part for Chinese 47/49CC engines (Increase your HP by 2hp - 3hp over your regular engine) Piston diameter :44 mm,piston pin length: 37 mm.please check with the size before your stock one Arrival within 1-2 days (Sold by GOOFIT and Fulfilled by Amazon) Arrival within 7-15 days (Ships from and sold by GOOFIT)