wouldnt know the difference got the kit from a store in town, payed 150 bucks for the flying horse 48cc kit and it just came with this cylinder head in the kit. im like LOL OK and i shoved it on before i ever ran it with the stock head, mind you i have the 48cc motor, it has the same if not more torque than my friends 66/80cc, we both have the baffle out cause it sounds more fun and its less restricted so free torque for a 2 stroke (take what torque i can get with a 2 stroke anyway would put an expansion chamber but nah dont want to be invested too much past keeping it running just for fun), im convinced its just a 66 not a 48 cause it does just as good, i wouldnt know the difference, didnt test the stock head but why would you, just put the shiny billet one on, best part is i got mine for like free with purchase, this flying horse kit did scare me during its break in hours, when it first fired up it made a horrible squealing grinding noise like a screw in the crank case almost, like it sounded like tearing cast aluminum, it ended up being way too tight of gear lash in the clutch and pinion, you know if gear lash is too tight gears make their own lash, by the time the cylinder loosened up the gear grinding was just a little whine, the wear pattern on the helical gears is terrible, the gear makes contact on the very outside edge, it has plenty of metal to wear down and wear in the middle like it should but you could tell the pinion and clutch were made in different factories with a communication issue, long story short i put moly grease in the gear set, its got some miles on it and these motors run awesome, the whole kit runs great. . .now i just got to get solid tubes cause air tires dont seem to last more than a few hours even slime filled ones