3 things to check. First, the on-ground static wide open runup rpm given by
the manufacture (and most before takeoff checklists) and done at every
annual should confirm correct pitch of the prop/ or condition of the engine
if not enough rpm is achieved. Secondly, when this static runup is done,
check the prop rpm with a prop tach to confirm that your engine tach is
giving you correct information. Just about any model airplane shop or
supplier can sell you or your mechanic one of these and they are fairly
accurate. More accurate than most 20 year old mechanical engine tachometers
for as low as $25 and can be done from the pilot's seat facing into the sun.
Thirdly, check the actual blade length and pitch per the TCD sheet for the
prop and aircraft using a prop protractor. All things to make you say,
"Hmmm".
"Nathan Young" wrote in message
...
I have a '71 PA28-180, with a fixed 60" pitch Sensenich prop. This is
the standard cruise prop for a PA28-180.

The POH indicates that 2700 RPM should only be able to be achieved
through 7000ft DA.

I am able to hit redline (2700 RPM) in level flight up to 11500 feet
density altitude. POH indicates that it should achieve about 2550.

It has operated this way as long as I can remember (several years) so
it is not a new phenomena.

So what could cause this? Prop pitch, poorly calibrated tach? Any
others? My plane has all of the K2U speed mods, so the reduced drag
probably plays a role.

I am able to achieve close to 150mph true airspeed at max cruise,
while the POH indicates 140mph for book. This makes me think the prop
RPM indications might be accurate.

Appreciate your thoughts.

Thanks,
Nathan