On Mon, 07 Jun 2004 15:32:29 GMT, Rick
wrote:

James Gemmill wrote:

Elevation of test, about 4000 feet above sea level ...

At that altitude you are producing considerably less than the rated sea
level power output to begin with. If the temperature of the intake air
is much above 45 degrees F you will lose even more.

The chances of burning exhaust valves at reduced power are pretty slim,
especially if the engine was not adjusted for altitude and is running rich.

Does the boat live at this altitude or did you just take it up to a
mountain lake for the weekend and found the performance less than you
expected?

The boat lives at 3545 but there is no water here, Arizona has water
in only a few places. I took it to lake Powell where elevation is a
little greater.

The mechanics are here at 3545 and one in Flagstaff at 7200.

Is your mechanic based at sea level or a local guy on the lake
who is familiar with local conditions and boats and knows your setup?

This might be a good tip, I'll checd with local mechanics at Lake
Powell next time I'm there.

Rick

James Gemmill wrote:
This might be a good tip, I'll checd with local mechanics at Lake
Powell next time I'm there.

If they are familiar with your boat/engine combination they should be
able to tell you if you are getting anywhere close to the performance
expected or possible under the conditions existing at the lake.

It sounds like the mechanic you mentioned my have just been stating the
published figures based on sea level performance. At high elevations and
temperatures your engine simply will not produce as much power as it
will at sea level conditions and may be effectively "overpropped."

There is a combination of prop size and rpm (maybe higher than 4600)
that will allow the engine to produce as much power as possible at the
lake but the boat will still not perform as well as the best prop/rpm
combination at sea level.

Good luck.

Rick