black/purple should have raised rpms..both low and high since its a stiffer spring, a couple delrin washers under the spring seat should fix the wandering rpms at full throttle, and so far with adding more helix the stock secondary spring cant hold up and its slipping the secondary.. the stock helix doesnt have enough initial angle...and maybe too much finish angle above about 6000 ft. from what testing I have done so far...I would think something in the 60/40/.36 up to about 8000 ft and then drop to a 58/38/.36 up above that..black/purple secondary, and your choice of a belly heavy weight..(11 series, belly busters or slp mtx weights....) would also try a slp blue/pink and green/pink primary spring with that combo as well...thinking might need the green/pink to get the bottom end real snappy again....oh..and so far..8300 pulls best from what I have seen..only problem is its real easy to get a rev limiter bog if you unload the track full throttle on a hill....if you know its gonna do it, and expect it..its not a biggy..performance wise..on back to back test (two identical stock 163 sleds) the one clutched to pull 8100 rpm on a steep deep climb just barely moving at the top (rider looking to start sidehilling or turn out)vrs the 8300 rpm sled which goes over the top with plenty of ground speed , and the rider thinking the hill wasnt even a challenge........
