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This is an actual photo of a Cessna 414 panel in cruise flight. The aircraft instruments and gauges are all properly functioning in straight and level coordinated flight. Both engines are approximately 50F below peak TIT (around 1640F) and are producing the same horsepower at the same RPM. Both engines are equipped with turboGAMIjector® fuel injectors. Notice that the left engine is burning 3.2 gallons per hour less fuel, with cooler cylinder head temperatures (black bars on left side of graphic engine monitor are 1 bar lower).
The left engine is running approximately 50F lean-of-peak TIT. The right engine is running approximately 50F rich-of-peak. At the same RPM (twin-engine aircraft) manifold pressure is increased approximately 3in. Hg. to produce the same horsepower while running lean-of-peak that the right engine makes rich-of-peak. This exhibits a valuable characteristic of a turbocharged engine - the ability to use additional available manifold pressure to produce equal horsepower lean-of-peak at lower RPM's. Similar results can be obtained with a normally aspirated engine if additional manifold pressure is available, however if at altitude or full thottle, The RPM may be increased approximately 100RPM to produce similar horsepower as above. Airspeed is relative to the percent of horsepower, so in order to produce the same percent of horsepower lean-of-peak, adjust manifold pressure or RPM as desired to achieve the same airspeed.
Lean-of-peak operation provides many significant benefits including:
More efficient engine operation (lower BSFC- brake specific fuel consumption):
For each pound of fuel consumed, more horsepower is produced.
Cylinder head temperatures at 50F lean-of-peak will be approximately 25-30F cooler than at 50F rich-of-peak. Excess air cools more efficiently. Cooler CHT's mean cooler valves and valve guides.
Fewer hydrocarbon deposits remain in the combustion chamber during and following combustion. Less wash down of oiled cylinder walls and fewer deposits throughout for improved valve/guide life and/or sticking.
Lower Peak Cylinder Pressures:
Peak cylinder pressures are the structural design limitations for cylinders. Operation lean-of-peak reduces the peak cylinder pressure approximately 7-8 percent at equivalent horsepower as rich-of-peak. This translates into lower stresses on the cylinders, bearings, and other engine components.
Fuel Savings/Increased Range or Payload:
In the above example (a Continental Motors 325hp TSIO-520NB engine) lean-of-peak operation provided 3.2gph fuel savings. The right engine was already equipped with GAMIjector® fuel injectors which allowed approximately a 1gph fuel savings!