I've just got through installing and tuning my QSC primary. I couldn't wait for my stock primary to fall off so I went ahead and put my QSC off my commander on.I got it tuned pretty close with some help from Adam at QSC. After mud nationals he said he would know exactly what needs to be done. This is what I have it doing know:launch is 8000 then it falls to 7700-7800 until about 65 mph where it falls to 7300. Then at 70 mph the rpms go up to 7900 and tops out at 80 mph and 8000 rpms.I guess the rpms falling at 65 mph is the secondary spring I've been hearing about.I tried to tune it out but all I can do is change the mph that it falls back at.I will probably be getting a STM secondary anyway.