IMHO you really don't need the 360... I can pretty much spank any O-360 RV-4 that I've flown with, especially in climb. Seriously, I've never wanted for more engine in my -3 and am very pleased with my Aero Sport Power IO-320. Even though the 360 is only 10-15 lbs heavier that is actually a lot of weight on an RV-3.