can I increase outboard hp?
 

O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Thanks!

can I increase outboard hp?
 

Going 100/1 on the mix won't get you anything.

All you need to do is get the parts list for both outboards and compare the
lists.
All the answers come to those that do the most homework.

-W

wrote in message
oups.com...
O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Thanks!

can I increase outboard hp?
 

wrote in message
oups.com...
O.K.: Urban myth or not?





Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Where'd you get that BS? Changing the mix will get you a scored cylinder.

can I increase outboard hp?
 

Even if the displacement is the same, there will be enough differences in
parts that the parts bill will exceed the cost of selling the one you have
and buying a 15. Additionally, your 7.5 will not have any more value at the
end of the exercise. Your call.
Steve

wrote in message
oups.com...
O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Thanks!

can I increase outboard hp?
 

Just thinking out loud here, but I'd "guess" this is an urban myth. It
seems easy enough to check, though.

Changing just the jets in the carburetor is not rocket science but it is
tricky - and you can end up with a useless carburetor if you make a
mistake. Instead, why not try installing a used carb from a 15hp motor
(larger jets and as you claim identical parts otherwise), seeing what
happens, and if you don't like the results, switching back to the
appropriate, original size. I wouldn't be too optimistic though.

The reason I don't think it would work is that horsepower is a function
of the amount of gasoline converted "efficiently" into smoke. It is the
pressure from the smoke that drives the pistons during the power stroke.
There is a physical limit to how much fuel a cylinder of a given size
can burn properly. Adding more than that would result in incomplete
combustion in the cylinder, fouled plugs, back firing and higher exhaust
manifold temperatures.

While it may be possible to increase the performance of your engine
slightly by using slightly larger jets then what are currently installed
(but perhaps not ones spec'd for twice the rated horsepower) my guess
is that you would also need to somehow adjust the timing as well as the
air entering the carob manifold, to maintain the proper air/gas ratio.

You could possibly achieve this by adding a blower (turbo) type
arrangement and adjusting the dwell, but I think we've now strayed in
way more effort than you had originally hoped for.

Oh, BTW, one side effect of "peaking" your engine performance,
generally, is reduced engine life. So what you gain in additional hp
tends to add stress and strain not originally intended for that hardware.

Hope this helps.

Cheers,

Robb






wrote:
O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Thanks!

can I increase outboard hp?
 

can I increase outboard hp?
 

trainfan1 wrote:
wrote:

O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.


You've heard wrong. That engine is a 6/7.5/8 hp. The conversion you
are wishing for is the 9.9 - to - 15 hp, those two are nearly identical
except for the carb and, on earlier models, the exhaust tuner.

Rob

That is the same thing that I heard (9.9 and 15 hp nearly identical).

Bill

can I increase outboard hp?
 

On Tue, 20 Jun 2006 04:43:45 -0400, Steven Shelikoff
wrote:

Actually, it might have more value in the end for people who boat on
lakes with a HP limit. Some of the ones around me have a 10hp limit and
a 7.5hp engine that actually puts out 15hp would be great.

====================

I have heard a few stories about people swapping out the motor cover
on a 15 or replacing the engine decals with a 9.9

can I increase outboard hp?
 

AMPowers wrote:
Just thinking out loud here, but I'd "guess" this is an urban myth. It
seems easy enough to check, though.

Changing just the jets in the carburetor is not rocket science but it is
tricky - and you can end up with a useless carburetor if you make a
mistake. Instead, why not try installing a used carb from a 15hp motor
(larger jets and as you claim identical parts otherwise), seeing what
happens, and if you don't like the results, switching back to the
appropriate, original size. I wouldn't be too optimistic though.

The reason I don't think it would work is that horsepower is a function
of the amount of gasoline converted "efficiently" into smoke. It is the
pressure from the smoke that drives the pistons during the power stroke.
There is a physical limit to how much fuel a cylinder of a given size
can burn properly. Adding more than that would result in incomplete
combustion in the cylinder, fouled plugs, back firing and higher exhaust
manifold temperatures.

While it may be possible to increase the performance of your engine
slightly by using slightly larger jets then what are currently installed
(but perhaps not ones spec'd for twice the rated horsepower) my guess
is that you would also need to somehow adjust the timing as well as the
air entering the carob manifold, to maintain the proper air/gas ratio.

You could possibly achieve this by adding a blower (turbo) type
arrangement and adjusting the dwell, but I think we've now strayed in
way more effort than you had originally hoped for.

Oh, BTW, one side effect of "peaking" your engine performance,
generally, is reduced engine life. So what you gain in additional hp
tends to add stress and strain not originally intended for that hardware.

Hope this helps.

Cheers,

Robb



All of this is true.

Now imagine that an engine manufacturer wants to offer a range of engine
sizes, but wants to minimize the cost of doing so. Make the 15 HP
motor, and install a smaller carb on it, and voila! you have a 9.9 hp
motor. This was the tactic followed by Johnson/Evinrude for a long time
( and is a common practice in the automotive industry as well... how
many V8 engines were sold with small 2 BBL carbs?).

Changing the jets will only screw up the mixture. The ratio of gas to
air is critical, and is carefully established by the jet size. The
AMOUNT of fuel/air mix is controlled by the size of the carb.

But Steve's advice about just getting a 15 HP motor is well worth
considering...

bob
s/v Eolian
Seattle

can I increase outboard hp?
 

Don't know about the 15 hp, but I do know that incresing fuel/air flow
increases hp for car engines.
I like the idea from Robb suggesting trying a carb off a larger motor.
Changing the mix won't increase hp. Variable Ratio Oil (VRO) pumps adjust
the mix from 50:1 to 100:1 based on manufacturer speced lubrication
requirements for the operating range RPMs.
Going to a 100:1 will burn cleaner, but not properly lubricate the engine
thru the RPM range.
MMC

wrote in message
oups.com...
O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Thanks!

can I increase outboard hp?
 

Thanks to all for the info. I will leave as-is for now, then add the
nitrous injection when I mount the supercharger...;-)

I got the changing the mix for added boost bit from motorcycles. Some
(amateur) racers I know cut down on the oil during time trials and
races to boost performance. I think it's only a couple of percent,
though. Could be yet another myth?

Hey, speaking of myths, maybe I'll try the cow-magnets, the Pro-lube
additive, Marvel Mystery Oil... or maybe I'll just go on a diet to
improve the weight:power ratio!

Ah, who needs to plane a dink anyway?

can I increase outboard hp?
 

wrote in message
oups.com...


I got the changing the mix for added boost bit from motorcycles. Some
(amateur) racers I know cut down on the oil during time trials and
races to boost performance. I think it's only a couple of percent,
though. Could be yet another myth?


There must be something to it ... although probably dangerous for the health
of the engine.

Ever notice how a chain saw engine starts to have more throttle response and
revs higher just as it is running out of gas/oil?

Eisboch

www.eisboch.com

can I increase outboard hp?
 

My brother had a Kawasaki 185 Enduro once. It had an oil reservoir and an
auto-oiler system for lubing the fuel for the 2-stroke. One day we were
riding and he was really excited! "Wow! The bike's going REALLY fast
today! I wonder why?" About 5 minutes later the motor seized up ...the
tube from the auto-oiler had fallen off. So yeah, running short on oil
gives you extra power ...for awhile. Race motors are pretty well abused
anyway, so making them temporarily 'do' with a little less oil for a race
wouldn't surprise me, especially in the class races where the motors all
have the same displacement and/or the races are shorter.

Brian


wrote in message
oups.com...
Thanks to all for the info. I will leave as-is for now, then add the
nitrous injection when I mount the supercharger...;-)

I got the changing the mix for added boost bit from motorcycles. Some
(amateur) racers I know cut down on the oil during time trials and
races to boost performance. I think it's only a couple of percent,
though. Could be yet another myth?

Hey, speaking of myths, maybe I'll try the cow-magnets, the Pro-lube
additive, Marvel Mystery Oil... or maybe I'll just go on a diet to
improve the weight:power ratio!

Ah, who needs to plane a dink anyway?

can I increase outboard hp?
 

the idea is that these motors use the same engine block ...do the researce
if that is true then you can do it but i suspect the cost will be more than
what is resonable
wrote in message
oups.com...
O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Thanks!

can I increase outboard hp?
 

can I increase outboard hp?
 

In article .com,
says...

O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Thanks!


DO NOT screw with the jets!!! That is not the answer. You need more
AIR and FUEL!!! Not more fuel. The differance is that the bore (throat)
and throttle plate are bigger in the 15hp carb. Take note they are
not 'Twice' as big. Air flow goes up as the square of the diameter.
If the hole was twice as big it would flow four times as much air.
The differance between the 9.9 carbs and 15 carbs is remarkably small.
Remember also it takes 3 to 4 times as much power to go twice as fast.
Changing your oil mix and getting 7.7 horsepower out of a 7.5 isn't
worth the risk of a scored and ruined engine. I ski behind my 70 h.p.
and I always run 40:1 instead of 50:1 because I run my engine hard.
It's a 1981 and never been apart!! If you want to get 7.7 out of that
7.5 switch to synthetic lower unit gear grease!! It helps!

Bless and best wishes.

can I increase outboard hp?
 

Try a flatter pitch prop. That will have as much or more effect than a fin
when trying to plane an inflatable.

David

can I increase outboard hp?
 

The only such conversion I have heard of that is documented is the Mercury
9.9 to 15. Bass and Walleye boats magazine did a write up on it last year
soemtime. It does not put out the same as a stock 15, but its close.


--
Bob La Londe
Fishing Arizona & The Colorado River
Fishing Forums & Contests
http://www.YumaBassMan.com



--
Posted via a free Usenet account from http://www.teranews.com

can I increase outboard hp?
 

can I increase outboard hp?
 

wrote in message
oups.com...
O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

I have a 1980-ish 7.5 seahorse that just does not have the guts to pop
my inflatable up on plane with two people and a full tank aboard. I
added those wings, which do help, but still just need a little more.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Thanks!

I was reading through the replies and did not see a couple suggestions that
(I feel) could gain you *some* HP- porting/polishing and changing the prop.

When I raced the 20 mod hydro class, porting (enlarging the intake and
exhaust passages) and polishing (smoothing all the passages to a mirror
finish) added substantial power and often made enough of a difference to
leave the others 'in the dust'. Mind you, this is not a racing O/B we're
talking about here, but all motors could benefit from a little 'cleaning up
the ports'.

You can also experiment with different props to see which one gets a better
'bite' and better uses the power of the O/B to benefit your use of the boat
(loading, speed, etc).

Just a thought.

Then again, you could just buy a bigger O/B :-)

Larry

My turbine powered boat project;
http://www.turbinefun.com

can I increase outboard hp?
 

a few years ago I was shown how to turn a 5hp merc into an 8hp motor
just by nbolting the exhaust manifold rotating it 180 degrees and
reinstalling it.

can I increase outboard hp?
 

How did you measure the horsepower?

Roger

http://home.insightbb.com/~derbyrm

"Drew Dalgleish" wrote in message
...
a few years ago I was shown how to turn a 5hp merc into an 8hp motor
just by nbolting the exhaust manifold rotating it 180 degrees and
reinstalling it.

can I increase outboard hp?
 

Drew Dalgleish wrote:
a few years ago I was shown how to turn a 5hp merc into an 8hp motor
just by nbolting the exhaust manifold rotating it 180 degrees and
reinstalling it.


For 2 and 4 stroke going back 2 decades, the 5 hp Merc is 1 cylinder,
the 8 hp is 2 cylinders.

can I increase outboard hp?
 

I took the mechanics word for it. It wasn't my motor and I didn't see
it in action . He did explain how and why he was doing it.

How did you measure the horsepower?

Roger

http://home.insightbb.com/~derbyrm

"Drew Dalgleish" wrote in message
...
a few years ago I was shown how to turn a 5hp merc into an 8hp motor
just by nbolting the exhaust manifold rotating it 180 degrees and
reinstalling it.

can I increase outboard hp?
 

And how long is your leg now.........


"Drew Dalgleish" wrote in message
...
I took the mechanics word for it. It wasn't my motor and I didn't see
it in action . He did explain how and why he was doing it.

How did you measure the horsepower?

Roger

http://home.insightbb.com/~derbyrm

"Drew Dalgleish" wrote in message
...
a few years ago I was shown how to turn a 5hp merc into an 8hp motor
just by nbolting the exhaust manifold rotating it 180 degrees and
reinstalling it.

can I increase outboard hp?
 

whatever you want to believe I guess. Perhaps you have a better reason
for turning the manifold over.

And how long is your leg now.........


"Drew Dalgleish" wrote in message
...
I took the mechanics word for it. It wasn't my motor and I didn't see
it in action . He did explain how and why he was doing it.

How did you measure the horsepower?

Roger

http://home.insightbb.com/~derbyrm

"Drew Dalgleish" wrote in message
...
a few years ago I was shown how to turn a 5hp merc into an 8hp motor
just by nbolting the exhaust manifold rotating it 180 degrees and
reinstalling it.

can I increase outboard hp?
 

Maybe an excuse to charge $75 per hour plus an additional fee for
"hotrodding" your o/b


"Drew Dalgleish" wrote in message
...
whatever you want to believe I guess. Perhaps you have a better reason
for turning the manifold over.

And how long is your leg now.........


"Drew Dalgleish" wrote in message
...
I took the mechanics word for it. It wasn't my motor and I didn't see
it in action . He did explain how and why he was doing it.

How did you measure the horsepower?

Roger

http://home.insightbb.com/~derbyrm

"Drew Dalgleish" wrote in message
.. .
a few years ago I was shown how to turn a 5hp merc into an 8hp motor
just by nbolting the exhaust manifold rotating it 180 degrees and
reinstalling it.

can I increase outboard hp?
 

On Sat, 24 Jun 2006 18:24:05 -0400, "John Cassara"
wrote:

Maybe an excuse to charge $75 per hour plus an additional fee for
"hotrodding" your o/b
Maybe but this guy works for $ 25 and I imagine that if the owner
didn't need a new prop he'd be ****ed

"Drew Dalgleish" wrote in message
...
whatever you want to believe I guess. Perhaps you have a better reason
for turning the manifold over.

And how long is your leg now.........


"Drew Dalgleish" wrote in message
...
I took the mechanics word for it. It wasn't my motor and I didn't see
it in action . He did explain how and why he was doing it.

How did you measure the horsepower?

Roger

http://home.insightbb.com/~derbyrm

"Drew Dalgleish" wrote in message
. ..
a few years ago I was shown how to turn a 5hp merc into an 8hp motor
just by nbolting the exhaust manifold rotating it 180 degrees and
reinstalling it.

can I increase outboard hp?
 

This is the cheapest HP boost you might find.

Test 1A % Increase or Reduction
Hydrocarbons - 40.4%
Carbon Monoxide - 42.6%
Oxides of Nitrogen - 18.2%
Horsepower + 4.3%

Test 2A % Increase or Reduction
Hydrocarbons - 43.6%
Carbon Monoxide - 34.3%
Oxides of Nitrogen - 20.2%
Horsepower + 5.2%

Test 3A % Increase or Reduction
Hydrocarbons - 31.9%
Carbon Monoxide - 25.0%
Oxides of Nitrogen - 15.3%
Horsepower + 5.6%

Test 4A % Increase or Reduction
Hydrocarbons - 53.0%
Carbon Monoxide - 28.2%
Oxides of Nitrogen - 16.5%
Horsepower + 6.5%

http://www.rxp-gas-kicker.com
Also reduces emissions and increases gas mileage according to the DOT.





wrote:
wrote:
O.K.: Urban myth or not?

I've heard over and over again that everything is the same on a 7.5
h.p. Johnson as on the 15 horse, except the carb. I also heard it's
not even the carb, it's just the jets.

Wrong on both counts.

If my memory is correct, the 7.5hp is about 10 cubic inches
displacement, the 9.9 and 15hp are about 15 ci. The 7.5 and 15 are
completely different engines except for maybe the ignition system
and/or some pieces of rubber or plastic.

The carb differences between these three engines are more than just the
jets, there's the size of the venturi too. To be blunt, anybody who
thinks that the only secret to getting 50-100% more power from an
engine is the carb jets does not know enough about engines to be
believed on almost anything thereunto appurtaining. You have been
misled by the uninformed.

Anybody actually done this carb or jets upgade, or at least seen it
work? Every dock rat seems to have heard of it, but nobody's done it.

The "jets upgrade" does not exist, which is why "nobody's done it."
The "carb upgrade" does work for engines for which the only difference
is indeed the carb. Otherwise you might need the "exhaust manifold
upgrade," the "reed plate upgrade," etc.

Failing that, any ideas on how to squeeze a bit more out of a
two-stroke (short of going 100:1 on the mix)?

Going 100:1 on the mix will not give you more power. People who soup-up
"fishing" motors to race them add more oil, not less. But simply
diddling the mix won't give you more power.

Your 7.5 morphed into the 8 hp motor with some tweaks, but that's not
the kind of power increase you're looking for. You need more cubic
inches, which means you need more metal around it, which means a
different outboard.

%mod%