Hey everybody. I'm a new motorized bicycle owner, got it last Saturday. It is an old ratty 12 speed bike with the 80/66cc HT engine kit. I bought it with the kit freshly installed and didn't get much with it. It has a 44t rear sprocket. I weigh +/- @240 lbs . Now....here is what I have experienced so far. I need the bike to go uphill halfway decent because I will be using it for a short commute to work. In stock form, it would barely make it up hills. Not good, some of my commute is uphill about a couple hundred meters or so. I decided to do a rear sprocket swap to a 60t that I found locally at Northern tool. After I bought the sprocket, I decided to do some exhaust and intake mods to increase my performance before swapping the sprocket. Today, I took the muffler apart, it is a black one. It was welded together. After grinding off the welds, I noticed what looks like an extremely crude catalytic converter insert at the end of the pipe. It was all held in, converter, baffle, and all by some spot welds inside the pipe. I removed everything (please no environmental speak about the converter removal. It really is a sorry excuse for one anyway) Then I opened up the exhaust and intake gaskets and did some contour work on the intake and exhaust pipe with a die grinder with a cone shaped carbide tip. Now, I can climb the same hills no problem at a decent speed and actually gain speed going up hills, although vveeerrryyy gradually; top speed is about 20 without really spinning up the motor. The power increase is VERY noticeable, but now its kind of loud for my taste; I will address that issue shortly with some kind of home made silencer added to the muffler somewhere. I feel like I need a little more grunt up those hills. How much difference would a 54t rear sprocket be? I think the 60t is overkill, and its going back tomorrow, but they stock a 54t one too. Will it give me a noticeable amount of torque? Top speed does not concern me, I will be driving it downtown.