Sea level to 6000 feet?
 

I have a Mercruiser Alpha One carbureted 6 cyl 190 hp motor on my boat.
Should I expect the boat to run normally at Lake Tahoe or will it need a
tune up each time I visit Lake Tahoe from sea level?
I've been told I don't need to alter the tuning if I switch props to one
with more torque when I visit Tahoe.

Bryan wrote:
I have a Mercruiser Alpha One carbureted 6 cyl 190 hp motor on my boat.
Should I expect the boat to run normally at Lake Tahoe or will it need a
tune up each time I visit Lake Tahoe from sea level?
I've been told I don't need to alter the tuning if I switch props to one
with more torque when I visit Tahoe.



A prop change should do fine, if you need it... it depends on how you
will use the boat. Figure about 2% power loss for each 1000 ASL.... or
about 168-169 HP at Tahoe.

Rob

trainfan1 wrote:
Bryan wrote:
I have a Mercruiser Alpha One carbureted 6 cyl 190 hp motor on my boat.
Should I expect the boat to run normally at Lake Tahoe or will it need a
tune up each time I visit Lake Tahoe from sea level?
I've been told I don't need to alter the tuning if I switch props to one
with more torque when I visit Tahoe.



A prop change should do fine, if you need it... it depends on how you
will use the boat. Figure about 2% power loss for each 1000 ASL.... or
about 168-169 HP at Tahoe.

Rob

A problem not usually encountered by sal****er boaters. :-)

On 14 Jul 2005 15:06:54 -0700, " wrote:



trainfan1 wrote:
Bryan wrote:
I have a Mercruiser Alpha One carbureted 6 cyl 190 hp motor on my boat.
Should I expect the boat to run normally at Lake Tahoe or will it need a
tune up each time I visit Lake Tahoe from sea level?
I've been told I don't need to alter the tuning if I switch props to one
with more torque when I visit Tahoe.



A prop change should do fine, if you need it... it depends on how you
will use the boat. Figure about 2% power loss for each 1000 ASL.... or
about 168-169 HP at Tahoe.

Rob

A problem not usually encountered by sal****er boaters. :-)

So if I go from the south end of the bay up to the north end, I don't need to
retune anything? Thank God!

--
John H.
On the 'PocoLoco' out of Deale, MD

In article ,
Bryan wrote:
:I have a Mercruiser Alpha One carbureted 6 cyl 190 hp motor on my boat.
:Should I expect the boat to run normally at Lake Tahoe or will it need a
:tune up each time I visit Lake Tahoe from sea level?
:I've been told I don't need to alter the tuning if I switch props to one
:with more torque when I visit Tahoe.

You will defintely lose power up here (I live in South Lake Tahoe). I
have and use two props...a 15x15 for sea level and lower elevation
(below about 4000') and a 15x17 for use in Tahoe. If I were to use the
15x15 prop in Tahoe, I would never reach my engine's WOT RPM spec.
Even when the correct prop is used, I lose about 20-25% power up here
as compared to sea level. My boat, a 17' runabout v-hull with a little
4 cylinder 130 hp Volvo AQ130C in it, goes from 32-33 mph WOT at sea
level down to about 27 mph WOT in Tahoe...and that is with the prop
change. I don't do any tuning for high elevation...I know you could
advance the timing slightly to improve performance a bit, but I don't,
and I don't think there is anything else I could do that would impact
high speed operation on this engine...if there is anything besides
that, I'd like to know about it.

I think you got your pitches backward. Less power = less pitch.


"Bob" wrote in message
...
In article ,
Bryan wrote:
:I have a Mercruiser Alpha One carbureted 6 cyl 190 hp motor on my boat.
:Should I expect the boat to run normally at Lake Tahoe or will it need a
:tune up each time I visit Lake Tahoe from sea level?
:I've been told I don't need to alter the tuning if I switch props to one
:with more torque when I visit Tahoe.

You will defintely lose power up here (I live in South Lake Tahoe). I
have and use two props...a 15x15 for sea level and lower elevation
(below about 4000') and a 15x17 for use in Tahoe. If I were to use the
15x15 prop in Tahoe, I would never reach my engine's WOT RPM spec.
Even when the correct prop is used, I lose about 20-25% power up here
as compared to sea level. My boat, a 17' runabout v-hull with a little
4 cylinder 130 hp Volvo AQ130C in it, goes from 32-33 mph WOT at sea
level down to about 27 mph WOT in Tahoe...and that is with the prop
change. I don't do any tuning for high elevation...I know you could
advance the timing slightly to improve performance a bit, but I don't,
and I don't think there is anything else I could do that would impact
high speed operation on this engine...if there is anything besides
that, I'd like to know about it.

Woodchuck wrote:

:I think you got your pitches backward. Less power = less pitch.

Yes, I do...thanks for the correction, Woodchuck.

"Bryan" wrote in message
...
I have a Mercruiser Alpha One carbureted 6 cyl 190 hp motor on my boat.
Should I expect the boat to run normally at Lake Tahoe or will it need a
tune up each time I visit Lake Tahoe from sea level?
I've been told I don't need to alter the tuning if I switch props to one
with more torque when I visit Tahoe.



You will need to do two things when you take your boat to Lake Tahoe.

1. You will need to adjust the idle stop screw on the throttle linkage on
your carburetor. It will be necessary to raise the idle setting so your
engine will idle at that altitude. This would not be necessary on an EFI
engine, but will be required for a carbureted one. Very simple to do, and
just takes a couple of minutes.

2. Assuming your boat is properly propped for sea level, you will need to
drop at least two inches of pitch, and more likely four inches to allow the
boat to operate in the proper RPM band while cruising at Tahoe's altitude.
Expect a very significant drop in overall performance.

You will lost a lot of Horse power. You could advance the timing or rejet
the carb. Since I run a V-8, I just take the boat. Where it will run 34 at
sea leavel, I get about 25 on Tahoe.

"Bryan" wrote in message
...
I have a Mercruiser Alpha One carbureted 6 cyl 190 hp motor on my boat.
Should I expect the boat to run normally at Lake Tahoe or will it need a
tune up each time I visit Lake Tahoe from sea level?
I've been told I don't need to alter the tuning if I switch props to one
with more torque when I visit Tahoe.