REFLECTOR: Fw: IO-550 Fuel Flow Issues and running LOP

[Dave Philipsen]

Scott Derrick wrote:

>Sid Knox wrote:
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>>This could be more than an annoyance at idle... it would be destructive with 
>>take-off power!
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>>To run too lean, full-power, at low altitudes is begging for detonation. 
>>With heavy detonation, cyl temps can hit 500F so quickly you may not even 
>>notice it before it is too late.
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>To clarify,  running too lean does not cause detonation, it causes the 
>engine to shut down.
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>Running between 50 LOP and 75 ROP causes detonation.  There is a bad 
>range that is rich of 50 LOP and lean of 75 ROP that can be harmful to 
>your engine.
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>Scott
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Additionally, I don't think you need to be quite so concerned with 
manifold pressure when you're running LOP.  Typically, we change MAP by 
adjusting the throttle (air intake) which varies the power output of the 
engine.  When you're running LOP, you can adjust power with your mixture 
control; the farther you lean from peak, the lower the power output.  
You can leave the throttle wide open.

As was mentioned on another forum recently, you can also improve fuel 
efficiency by cruising at best glide speed (indicated) or Vx.  At this 
speed your airplane has the least drag and although it may seem slow 
(maybe 110 kts or so) it is an _indicated_ speed so you can improve your 
groundspeed by flying at higher altitudes.

Another thing I learned when reading John Deakin's articles is that the 
"red box" between 50 LOP and 75 ROP is virtually eliminated at or above 
8000 feet for a normally aspirated engine since it's pretty much 
impossible for your engine to develop that much power up there.