NO ITS NOT WORTH THE 120 extra dollars!!!! The 50cc 4-stroke engine kits are a scam. The only 4-stroke kits that are worth ANYTHING are the kits like this one. But to be completely honest, even though the 4-stroke motorized bikes are "more reliable," they do not last nearly as long as the 2-stroke kits which are literally half the price. If you are going to get another kit, id definitely go with the Wildcat pk80. it's a 2-stroke kit that is known to last THOUSANDS of miles if properly maintained, and will also give MUCH more power and top speed than almost any 4-stroke kit.