How's the compression??
The 58/116 like props that let them spin up, shoot for at least mid 6's on the ground for the 116 and around 7 for the 58.
If you do not have adequate air flow and especially good extraction it is not good to run a new engine on the ground for extended periods, you have learned this so now just put the plane in the air and have fun. When the prop un-loads you might be surprised. BMEs like/need to spin a little more than some others for peak torque