Possibly Cessna and Piper have not seen your chart. I have several POHs he

An Arrow PA28R-201 POH shows 75% power, full throttle, at 6,000 feet/2400 RPM
and 7,500/2700 RPM. 65% power at about 9,800/2400 and 12,000/2700. (IO-360/200
Lyc.)

A Cessna 182T (T-model, not T for turbo) POH has tables that are a little harder
to read than the Arrow's graphs, but the highest % power they show at 8,000 feet
is 74% and at 12,000 feet 64%. (IO-540/230 Lyc.)

A carburated Cherokee Six/260 shows 75% power, full throttle, at 8,300 feet and
65% power at 11,200 feet. Engine RPM is not stated. (O-540/260 Lyc.)

I also have a tiny and very complicated power chart from Lycoming for the O-540
but I am too lazy to figure it out.

I am no fluid dynamicist (and may be about to prove it), but my dim
understanding is that the Reynolds number has a major effect on fluid flow and
in its calculation there is a density term. Certainly the mixture velocities at
various points in each different intake system would be different. Velocity is
also a term in the Reynolds number calculation. So (leaping) it does not
surprise me that intake systems with different geometries would perform at least
slightly differently at different altitudes. Exhaust systems, too, I'd guess.

Possibly I should have been more diplomatic in how I suggested that the OP
needed a POH but that still seems to me to be the case.

On 10/21/2006 12:46 PM, Bob Moore wrote the following:
Mitty wrote
You don't have a POH?

You know, he might not even have an airplane. He just asked
a question and expected an answer, not a wise crack.

No POH required, answer is not aircraft specific, see:

http://www.kellyaerospace.com/articl...bocharging.pdf

Bob Moore