LOP operations simplified...
I sucked out the best info from the EI manual and adjusted it for us IO-390 users. You can adjust the numbers to suit any engine/HP as needed. I have used LOP for a while now and couldn't imagine throwing away the extra $fuel$ with ROP operations!! Hope this helps someone.
Travis
Click to enlarge the image:
IO-390 215 HP Engine
(75% power output = 161.25 HP)
100 degrees ROP =
Best Power = 13.061 GPH (.081 * HP = BSFC Gal/HR)
62 degrees LOP =
Best Economy = 9.067 GPH (.060 * HP = BSFC Gal/HR)
3.994 GPH savings operating LOP over ROP at 75% power!
** Must adjust LOP RPM/MP settings as needed for 75% power, different setting than ROP 75% power **
There are many leaning methods available. Below are a number of them for your consideration:
The ?Best Power? Leaning Method:
Set the mixture so the leanest cylinder operates 1000F rich of peak EGT (see chart). This
method helps ensure the exhaust valves stay reasonably cool. The engine will produce maximum
power for a given throttle setting. Of all the leaning methods presented, this method will produce
the highest airspeed, fuel consumption and CHT?s.
For engines that have a wide fuel/air distribution between cylinders (such as carbureted engines
and some injected engines), this method may result in some of the cylinders running very rich.
These rich cylinders can produce carbon deposits and fouled plugs. If this is the case for your engine,
you may want to consider a leaner operating method.
The ?Peak EGT? Leaning Method:
Set the mixture so the leanest cylinder operates at peak EGT. At this mixture setting the EGTs
will be 1000F hotter than the ?Best Power? leaning method? (see chart). This method results
in the highest temperature on the exhaust valves and heat damage could become an issue. The
engine will produce approximately 4% less power and the fuel consumption will be approximately
14% lower than with the ?1000F Rich-of-Peak (ROP) Leaning Method.? The CHTs will be near
there highest.
The ?Lean-of-Peak (LOP)? Leaning Method:
Set the mixture so the richest cylinder operates at 30-800F lean of peak EGT. At this mixture
setting the CHTs will be the coolest and the EGT will be 20-700F hotter than the ?1000F Rich-of-
Peak (ROP) Leaning Method? (see chart). This method results in reasonably cool exhaust
valve temperatures. The engine will produce approximately 7+% less power and the fuel
consumption will be 20+% lower than with the ?Best Power? leaning method.?
The ?LOP with Power Recovery? Leaning Method:
Set the mixture so the richest cylinder operates at 30-800F lean of peak EGT. Increase the manifold
pressure by 1.25" Hg to recover 5% of the power loss (.25" Hg per %H.P.). It is important the richest
cylinder is not allowed to drift within 300F of peak EGT (refer to the detonation survey for your engine).
It must remain at LOP operation. The lean mixture is required for all cylinders to ensure that detonation does not occur. The higher the power recovery, the higher the chance of detonation.
The fuel consumption and power achieved for an engine by using one of the leaning methods outlined
above may vary depending on the fuel/air distribution between cylinders of that engine. For example: A
carbureted engine power may not change much as it is leaned past the best power mixture. As the engine is leaned, the leaner cylinders will lose power as the richer cylinders gain power. Also, the specific fuel consumption for some cylinders may be at best economy while the other cylinders will be at best power or richer. Therefore, the specific fuel consumption for the engine will be more than that shown in the chart.
