IO-470 Power Settings

[Rob58]

There have been some posts about certain RPM setting to avoid when you are flying behind an IO-520. I'm wondering if the same cautions apply to the IO-470? I am often very happy to run 55-65% power. Some articles by Mike Busch suggest running lower RPM / higher MP settings is a good approach - I think this is referred to as "oversquare". My POH says running 2200 RPM / 24" MP gives me 65% at 5000 ft. the idea of the prop turning slow is certainly appealing, but what experience have you guys had? Are there any sweet spots? Any combinations to stay away from?

 

[Pilawt]

Consult the manual for your specific airplane and engine, of course. But for an example, here's the MP/RPM diagram from the POH for my old K35 Bonanza (IO-470-C). I felt the best balance of performance, efficiency and smoothness in that airplane was around 2300 rpm. YMMV.

 

[Rob58]

Thanks for the feedback. Makes sense - find a setting that feels the smoothest.

 

[coloradobluesky]

I use "Don't get more than 5" of manifold different" guideline. So you can do 2000 rpm with 25" of manifold for most oversquare. Its the same as running a car in high gear and high throttle setting as in pulling a hill in high gear and flooring it. Lug it. Doesn't hurt a thing. Saves on gas. Might hurt something if you overdo it. Seems a little weird. So limit it by some common sense amount. 2000/25" is plenty oversquare. Stick to that or less than 5 you will be OK.

I run mine where it runs with the least vibration. Tried them all and have two that are the smoothest so I use those. Others work too.