New Cylinder AD's released by FAA

[jdeakin]

If the engine is run as per the book you generally don't have problems.

If you run at or below 60% of rated power (maybe 65%), and if you pay a little bit of attention to cooling (baffles), and if you don't care about wasting 2 to 3 GPH (7.5 to 11.3 LPH), and if you don't care about running about 30℉ (17℃) hotter, then you are correct.

On the other hand, if you set up the SAME HP, LOP, the engine will run 30℉ COOLER, enjoy much lower PEAK combustion pressure, and use about 3 GPH LESS fuel. You can prove this in any twin, with engine monitors.

That's pretty close to paying for a new engine at TBO at US prices.

The engine is designed around the px in the chambers.

A true statement.

The bearings will fail before the head.

Got data? I've never seen bearings fail, except from catastrophic events (Oil starvation, Crankshaft failures, or a mechanic who fails to put "keeper" on the engine when a cylinder is removed, etc.)

Rapid cooling is something else which is hard on an engine. Flight schools and meat bomb aircraft suffer the worst cracking.

Exactly the opposite. Those aircraft generally go to TBO and beyond, mostly (entirely?) because they spend their whole lives at full power and properly ROP in the climb, OR idle power, where mixture is not important. "Shock Cooling" is a myth.

Now, if you want to run the CHTs up to redline, and then chop the power, THAT may be "Shock Cooling," but I just call it "abuse."

So which will crack first. If you have an aircraft that is px to a max diff of 8.5 psi and you fly it un pressurized will it crack more at max diff or with no px in the cabin.

I'm trying and failing to see any relevance to the subject at hand. But if you operate any aircraft designed for 8.5 psid at ambient pressure (0.0 psid) instead, you will generally have more problems with the pressurized aircraft due to the pressure (The Aloha "Pop-Top" comes to mind). But with proper maintenance and corrosion control, you probably won't see cracks at all in either aircraft.

John Deakin
jdeakin // at // advancedpilot.com