IMO it is essential that the drive is mounted at the proper X dimension, we have had two 18's set up with the drive. Steve Mars was setup as it was intended, his best speed with a 300 SB was 78-79. In contrast DonCig built one with about 175 HP more and only achieved a few MPH more, the problem lies in the fact that the drive must be mounted with a 17-1/2" X to realize the full potential of the drive. It must be at this height to keep only the fin and blades in the water flow, if any part of the bullet/case is in the water flow it produces stern lift stealing several MPH off the top end. I ran a BH on my 22 for a season, mine being an old Tempest 300 setup has an X is just shy of 17", I loved the drive the handling was superb along with the complete absence of torque steer. The boat ran great low to upper mid range then ran to flat due to the stern lift, out of the hole was as good if not slightly better than the Bravo X I now run. You need to do some searching for the posts on both 18's to see the facts of just how important the raised X is, DonCig and waleyetwo. Don did not raise his X as he did not want the redo the boat which I can more than understand, but it cost him about five MPH.
No matter what your beliefs are "GOD BLESS AMERICA"
Fully retired marine tech near 60 years in the biz.