Life, scroll down a few posts and read the lengthy post from Gohard. Its a long read but there is a ton of info in there. Clutch set ups....Im no expert but I have been playing with set ups. Biggest gain with a primary I found was the ability to tune optimally for high range or low range, the smaller one way bearing( this gave better starting ratio) and definately better belt pinch. I cruise around alot in high range with 30" zillas so never having issues in high with tall tire is very nice. having suddenly enough power to wheely your max definatly lets you know you are transferring power to the rear tires. This is about efficiency. By that I mean setting up the clutches to optimize where your engine makes the most power. Thats probably what your dyno guy was trying to set up. Secondary, got the STM and its very shiny LOL, but the biggest gain I saw was the ability to let off the throttle and punch it again, and instantly back in optimum power rpms very quickly. Was it worth it????? NOt totally sure but I got it so it is a definate gain. It too has the ability to change the helix angle ( purchase different ones ) and optimize clutch tuning. Set up for fast trails, mud etc. You do lose some engine breaking over the factory secondary. Just some thoughts without getting too technical. :black2: