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Kyle:
You understand that correctly. To keep ICPs under control at 75% power you need to be richer than about 125dF ROP or leaner than about 20dF LOP. Doing so is beneficial to longevity. The Red box grows as power increases and it shrinks as power decreases until it no longer exists somewhere between 60 and 65% power. To follow the science, you must either allow range to suffer or be able to run LOP at power settings above 60-65%. That's why the manufacturer's recommended cruise power settings are as low as they are.
The Manufacturer's MARKETING Department's recommendations of 50dF ROP at 75% power are not, in our view, a good idea based on the observations we have made over many hunderds of hours of test cell work and the field observations. If longevity is not an issue, then 25-50dF ROP is the mixture setting that will result in the best trade-off between airspeed and range--just like the Marketing Department suggests.
Those who have been operating at high powers LOP have been getting excellent results because range and speed are both better while keeping ICPs controlled for increased longevity. I routinely run between 85 and 90% power in cruise with a cool engine and good range. My engine is pristine clean with no buildup of anything on the pistons, or valves. The oil stays clear for 20-25 hours. You can acheive the same longevity with very rich mixtures, but the engine will run a lot dirtier. ROP is OK if you are rich enough. It will result in higher maintenance since it will have much more deposits in the combustion chamber and the oil will get dirtier quicker. I donlt have any hard data, but it makes sense that clean oil is better than dirty oil.
According to Carl Goulet, former VP of Engineering at TCM, "Cooler is better. Cleaner is better. LOP is cooler and cleaner." His position is certainly in harmony with the science as we have observed it. <g>
Regards,
__________________
Walter Atkinson
Advanced Pilot Seminars
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