I have a 2011 RZR 4 800 that I put a GSXR 750 motor in. I tried the chain and sprocket route and was not happy with the gearing so I had a part machined to run the apex primary. I also installed a STM secondary. I have the lightest Yamaha spring in my primary and 104 grams of weight per arm. My problem is I cannot get over 55 mph and all the apex swap guys say they can go 80-90 mph. I run it in sixth gear all the time through my stock Polaris trans. Anyone have any ideas?