The 3.55 gars will be allright at 85 with a five speed just a few more rev's. 800lbs is a lot of weight which will make a difference in racing. You should have more than 320hp thats not much for a blown 5.0. Taking the belt off the blower will not give you a good comparison because at higher rev's the the blower is a restriction to the intake and make the motor run rich and flatten out. The belt fell off my truck and it only went up to 3000rpm before engine missfire. How high is your fuel there. We have got 91,96,98 octane but the 98 is only in the north island dam it need it in the south island for my truck, high compression only run 5lbs boost, even on a hot day she will pink on 96. Put the boost gauge on it and see what she has got depends on compression ratio to how high you can go before you start to detonate, or timing, best to set it on the road but don't kill it with, Oh my god this goes better and better with more boost untill it pops.