First let me say that the 150 GY6 engine was originally designed for the much lighter scooter and add to that that all the performance parts were designed for the scooter. Second on average with any stock engine your air fuel only fills cylinder approximately 50-55%, so the trick to performance is to fill the cylinder as close to 100% as possible. With a naturally aspirated engine you will only get approximately 80-85 percent charge in the cylinder. Any more than that it needs to be aided with a turbo or supercharger. For a bored or even stroked engine to realize more power you will need more flow into and out of the engine. The more the cylinder fills with a/f the more power but that bigger charge when burned has to exit the engine quicker so that the cylinder cycle can start with a clean fresh charge of a/f. As I have stated many times my 150 has a 63mm bore and 6mm stroke with a large valve ported head and running every available cam out there. It was quicker and more powerful than stock but still was not what I expected. I wanted more power and speed but it just wasn't happening. All Chinese and Taiwanese cams are sold with useless specs for they do not come with the timing degree specs and that makes it impossible to degree the cam for optimum performance. When I brought my cams to the cam shop for them to figure the timing events I found that all the performance cams were really mild grinds. The cam I have now has 34 degrees overlap which is 4 times of what is available. This is what woke my 150 up. In fact when doing top speed runs I was running lean with a 30mm and 32mm carb. I currently run a 34mm Mikuni slide carb. Now when I nail it from a dead stop on grass I'm slinging grass leaving 20' tracks down to the dirt. Top speed is 50 + mph @ 9200 rpm running the stock sprockets, 308 ratio final drive gears and 16 gram rollers. The point is that if you want performance it will depend on what you are willing to pay for that performance, how much patients you have and getting the best parts available. It has been 7 years since my last build and the engine has held up. Performance = money weather your building a buggy or car.
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