RE: OS 91 VRDF - care and feeding
In the DF world, we ran these on 5-10% nitro with the stick head shim package. You may also want to clearance the big end of the rod to get .003". If not the bearing could peel out of the rod at high rpm. I have seen that and the results are ugly.
I had one that the sleeve was tapered on the outside up to the ports to in effect create more flow behind the port. That made a difference in topend but also consistency.