RE: SJ 60LX & H9 P51
rpms are low for the engine ..... need to drop the prop size for a while. You noted the 9x9 was up way over 18,500 and launching at 17,500+ - that is right on the money. The 10x7 should be over 17,000.
Im a bit confused though..... ground rpm should not vary more than 100-200 rpm whether it has the diverter on it or not... only difference tends to be whether it ends up running hot when it unloads.
Without any diverter is best. The big diverter should not make any rpm difference at all. Small diameter will drop rpm a few.