while testing my 921 last weekend we saw first hand the rpm gains/lost and belt clamp gained and lost by simply playing from click 2-3-4...
best combo was my SHR968A weights (MXZ) with an extra 5 grams added/stock spring and a 15 gram cross bolt on clicker 4/SHR helix, spring......
base combo was the SHR967A at 3 grams per and click 3/SHR helix, spring but the low end revvyness was to much for the TQ of the BB...
the SHR/MPI850 turbo LOVED the SHR967A at 51 grams/click 3/stock spring/SHR helix, spring...
MINIMAL turbo lag/instant RPM and track speed and "quicker" throttle response from part throttle...
EVERY turbo 850 needs these
conditions- 9600', 55 degrees, mashed potatoes...BJ