Cruise Setting for Normally Aspirated 337

[patrolpilot]

This question has been on my mind, and the same recent topic for the P337 has made me jump in with a similar question for the mouth breather.

What RPM and/or horsepower do you prefer for cruise flight?

I've been using 2600 RPM. That practice was passed down to me from the previous owner, who had it passed on to him. I saw it in practice when I took the seller home, a decent length flight.

I pondered it against a slower RPM, but the bottom line is that these guys ran the engines 1000 hours beyond TBO without issues. I've done enough cross-country flying that I've been able to try different RPMs, with MP that produce 75% or less power. Typically, I fly the airplane at 8,000 to 11,000'. So, in reality, I'm looking at 60% to 70%.

I've tried 2500, 2400, 2300, and 2200. At 2200 and 2300 RPM, while at altitude (reference is probably funny for a "P" flyer), it seems like the airplane is floundering. It has a tough time recovering from chop or turbulence, and the pitch attitude seems higher than it should be.

Here is how my airplane performs against the book at 2600, 2500, and 2400 RPM. At 2600 RPM, I'm always a solid 3 knots faster. 2500 is close to book, and 2400 at least 3 knots slower. Each progressive decrease increases the pitch, of course, but at the 2600 RPM, it seems as flat as a pancake compared to the other two.

I've never experienced "heat" issues, but with the factory gauges, I would say that the lower RPMs are slightly hotter. I think that is a product of pitch attitude and reduced airflow.

As I pondered this over coffee, I thought about comparing just how many times the engine completes a revolution on my typical flight stage length. I didn't consider the climb or descent as the profiles for those segments is the same. It really surprised me how much less the engine turns at the higher RPMs. I made the calculations with the book values, not the gains or losses I've observed. (attached)

So, how do you manage your power choice?