Keep in mind the specs given for the GY6 is bench rated @ 14 HP and chasis rated @ 9HP. I have been looking for acess to a dyno for some time but no one around here has a small dyno. By what I have done to my engine I figure mathmatically I am somewhere near double HP for this engine. There is a formuls online to figure horsepower but is set up for 1/4 and 1/8 mile runs so you have to find someone really proficient to tweek the formulas to fit a shorter run. I personally would not recomend the 63mm cylinder since these kits have material cut from the protruding portion of the sleeve for it to fit a bored out case. Also do not use the 61mm drop in kit for the same reason. That portion of the sleeve is where all the remaining heat is transfered then cooled by the splashing oil. This is also where most side force is applied during the reversing transition of the piston. There is a lot of side pressure in this area then add the thin sleeve with the added heat it will eventually end in disaster. The exception is if you were to send the kit out and have the cast sleeve cut out and a quality steel sleeve made and pressed in, but on top of the price for the kit you will add 250.00 to do this. I will recomend a quality 62mm kit but the case will have to be bored out for this to fit. You will want the 60mm or 61mm crank. If you are going to push it to the limits exceeding 8500 rpm constantly I would recomend one with the forged rod. Some do sell a 6mm and 8mm stroked crank. I have the 6mm in my buggy but it came as a kit with a longer cylinder to compensate for the taller deck height needed. I cannot find these kits anymore. The 2mm or 3mm stroke will require a spacer to acheive proper deck height. The 6mm and 8mm if spacers are used the sleeve is too short on the lower end and will be a problem in time for the more you space the jug to acheive proper deck height the sleeve is lifted from case and piston transition is too close to bottom of sleeve. Most of your power will come from the head, cam, exhaust and fuel system, but you have to think of where you will require most of your power. For example if your into climbing hills you will want your powerband to be closer to the bottom but if you are looking for top end on trails you will want the powerband higher. This will be determined largly by the type of cam and if a port and polish is done to the head, how the porting is done. Hope this has answered most of your questions, if not give me a call and I can set you in the right direction.
TOM
662-301-1563
|