| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 316.1 | Try it!! | STAFF::CHACE | let's go fishin' | Wed Mar 22 1989 14:28 | 8 |
|
I skied alot behind a 18 hp Johnson when I was younger. It was
on a 14' open fiberglass boat, which was probably at *least* as
heavy as your aluminum one. I would think that 'Dad' would have
no problem skiing behind this boat. It just may be a little slow
pulling him up.
Kenny
|
| 316.2 | There is a HP kit | ANT::RBEDARD | | Mon Mar 27 1989 12:31 | 9 |
| Johnson offers kits for engines using the same powerhead to
move to the next HP level.
The kits contain a new carburetor and I think the reed plate.
Although the reed plate is not always needed, sometimes a restrictor
gasket is used between the old carb and plate. Just removing the restrictor
will not increase the HP, the bigger carb is needed.
Ron
|
| 316.3 | cheap dirty trick | SICVAX::SCHEIBEL | U can Teach A new dog UL TRIX | Fri Mar 31 1989 14:49 | 5 |
| You could try rejeting the carborator and giveing the motor more air by
removing the silencer on the front of motor.
Bill
|
| 316.4 | Change the head and advance the timing *usually* | CSMET2::CHACE | let's go fishin' | Fri Mar 31 1989 16:45 | 20 |
|
Removing the air/water baffle on the carb intake and then re-jetting
(you HAVE to rejet if you do this if you want your motor to live)
probably will give a little more power, but if the exhaust isn't
similarly changed to reflect this, the difference will be fairly
small at best.
On the motors which have the same displacement but come in different
horsepower ratings, the differences are often ALL of these:
Greater compression - usually from a different head
Different port timing and/or size - more exhaust duration
More ignition timing at high speeds
Notice on most of these motors the higher horsepower version
develops it's full hp at higher RPM. This is fine but there is usually
a drop in low-speed pulling power. Of course you'll never hear about
this - outboard motor torque output is not discussed, but it's TORQUE
that gives ACCELERATION!
Kenny_owner_of_a_9.9_aka_15_Johnson
|
| 316.5 | Thanks for the info | CSSE32::DORSEY | | Mon Apr 03 1989 15:06 | 22 |
|
The last reply supports info I got from Fernald's Marine who
told me that for some applications and engines lower horsepower
versions pull better than the higher hp version. But, they were
reluctant to specificly compare the Johnson 20, 25 and 30. The
20 and 25 both reach max hp in the same RPM range but the 30
reaches max hp at a higher range. I don't know about max torque
values. Part of the reason I asked my question was that I'm not
convinced I'd gain any benefit from modifying the engine for the
problem I'm trying to solve.
I think I'll take the advise of .1 and try it as is. I don't think
we'll take the water skiing too seriously and we can always make
a big pair of skis. Also, when I was a kid, a friend had an underpowered
boat abd we had a lot of fun on a disk and a pair of really big
crude skis. As he went through an infinite series of upgrades, it
never seemed that the increase in fun matched the increase in
expense.
Thanks for the advise/info.
Jack
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