"Leonard Ellis" wrote in message
m...
We're nearing time to overhaul the Lycoming O-320H2AD (6210 hours since
new) in our C172N. This will be its 3rd major overhaul and we're
interested in learning about the experiences of those who upgraded to the
O-360. Specifically, the changes you found in performance, impacts on
range, or other relevant information including recommendations on where to
get it done will be appreciated.

Cheers,
Leonard Ellis
Dallas, Texas

I've never flown a 180 hp 172, but the math indicates the 20 hp increase
will net you a 4% increase in speed. Since speed increase is proportionate
to the cube root of the ratio of the horsepowers, it should equal
(180/160)^(1/3) = 1.04 = 104%. That's about 5 knots on a 115 knot airplane.

On a 2,000 lb C-172, a 20 hp increase will net about 264 fpm. Alternately,
about 210 fpm at 2,500 lbs. The math is based on the fact that 1 hp will
lift 1 pound 33,000 ft in a minute. So, 20 hp will lift a 2,000 lb airplane
= 20 x 33,000/2,000 = 330 fpm, but you need to reduce that by multiplying it
by a prop efficiency factor. If we assume 80% efficiency, then the
increased rate of climb = 264 fpm.

One thing you should keep in mind is that a "tired" 0-320 probably isn't
producing 160 hp. So, a rebuild would net you a performance increase over
what you currently experience. An upgrade would net you an even bigger
performance increase.

KB