Just picked up a 2006 SS 24V with Indmar 8.1. The stock ACME 497 13x17.5 is not impressive out of the hole and only turns 4800 rpm at 50 mph with an 800lb load. Thought the 8.1 could run better so called Supra, Indmar, Acme, Wakemakers, and Bakes to help make a new prop selection. Very long story very short....... not much knowledge out there on propping the 8.1. I got suggestions of 13x16, 14x15.5, and 14x14.25 from a flow chart based on usage or simply they said I can't surf and foot behind the same prop. Guys......that's why I bought the 8.1. 450hp, 525 lb ft of torque, and revs to 5400 rpm can do a lot. Thats 125hp, 175lb ft, and 600 more rpms than the 5.7 Assault motor. After much online reading about others' 8.1 driven prop experiments and significant calculation regarding pitch, diameter, cup, RPM, and finally slip percentage estimation, I made a choice. The ACME 1273, 14.5x14.25, .150 cup, arrives tomorrow and I will record RPM and MPH info on both props to share with the forum. The lower pitch pulls harder, the larger diameter moves more water, the increased cup controls high speed RPM. My calculations show the 1273 will run 48mph at 5200 rpm with a barefooting load and carry 3000lb surf ballast at 11mph easily for the surfers. Fingers crossed!