There are two upgrades I am aware of (John Jewell and Norland) for C182 NA engines, both of which move the redline to 2625 rpm (from the stock 2500). The engine volume stays the same. While higher revs help with the take-off and initial climb, how can that help a cruise climb at 15,000 ft, as some people are reporting? If it does help with the cruise climb at high altitudes, wouldn't you have to set the prop to 2625, which is not really good for the engine (for an extended period)? Would like to hear some more wisdom here.