It's almost certain that your tach reads higher that the real engine
RPM by about 200. Provided that you leaned properly, the best
indication of real engine power output is your fuel burn, which is low.
Your airspeed agrees with the lower fuel burn number.

The first thing you should do is to get the tach checked.

Ross Oliver wrote:
Last week I flew my Grob from San Jose (RHV) to Torrance (TOA)
and back. Total time was nearly 6 hours, but burned
only about 30 gallons of fuel. The book says 9 gallons per
hour at 75% cruise. I've noticed this before, that it never
burns nearly as much fuel as I would expect. Another thing I
noticed during the flight that I had never thought much about
before is that in cruise, the throttle is about 3/4 closed, even
at 2600 RPM at 7500 feet MSL. Redline is 2700, and opening the
throttle further would push past redline. I haven't flown any
other planes in a while, so I can't recall whether this
throttle position is unusual.

All this seems to say that I am cruising around at Best Economy
(which the book says is 45%, 5.3 gal/hr). This would also explain
why I get only 105 kts IAS, rather than 115-120. I would
surely like to go faster, but I can't figure out how without
exceeding redline RPM. Is my tach in error? Do I need a different
prop? (fixed pitch) What else should I be checking? The engine
is a Lycoming O-320, same as a Warrior.


Happy landings,
Ross Oliver