On another thread, I asked about a 2 stroke vs. a 4 stroke for flats
fishing. Lots of "up on plane, get going .. stop .. do it again" etc. I run
in 18 inches of water or less most of the time.

One respondent brings up the theory that "four strokes can and do produce
better "thrust"". Is that theory correct?

In my original posting, I clearly needed/want hole shot..not better gas
mileage..more quiet..less pollution, or top end speed. Right now, in the
couple of groups in which I posted the original question...the vote is 27 to
3 votes in favor of 2 stokes over 4 strokes??????. If his theory is
correct...the 27 to 3 seems wrong for my particular needs. any comments are
much appreciated.. thanks

Four strokes tend to have more low-end "grunt" and a smoother power curve.
Two strokes tend to have a more pronounced "powerband".

That said on a boat that's propped right - a 2-stroke gets into the
powerband on the hole shot.

My boat (running a VERY old 2-stroke) is propped to 5600 rpm WOT (don't mean
I run it there often) and my hole shot is "explosive" to say the least.

-W

"RG" wrote in message
...
On another thread, I asked about a 2 stroke vs. a 4 stroke for flats
fishing. Lots of "up on plane, get going .. stop .. do it again" etc. I
run
in 18 inches of water or less most of the time.

One respondent brings up the theory that "four strokes can and do produce
better "thrust"". Is that theory correct?

In my original posting, I clearly needed/want hole shot..not better gas
mileage..more quiet..less pollution, or top end speed. Right now, in the
couple of groups in which I posted the original question...the vote is 27
to
3 votes in favor of 2 stokes over 4 strokes??????. If his theory is
correct...the 27 to 3 seems wrong for my particular needs. any comments
are
much appreciated.. thanks

You want to do hole shots in 18" of water or less? You should choose the motor
with the cheapest prop and lower unit.

RG wrote:
On another thread, I asked about a 2 stroke vs. a 4 stroke for flats
fishing. Lots of "up on plane, get going .. stop .. do it again" etc. I run
in 18 inches of water or less most of the time.

One respondent brings up the theory that "four strokes can and do produce
better "thrust"". Is that theory correct?

In my original posting, I clearly needed/want hole shot..not better gas
mileage..more quiet..less pollution, or top end speed. Right now, in the
couple of groups in which I posted the original question...the vote is 27 to
3 votes in favor of 2 stokes over 4 strokes??????. If his theory is
correct...the 27 to 3 seems wrong for my particular needs. any comments are
much appreciated.. thanks



Not really the thrust is a function of the propeller & what type of
engine turns it. Propellers with lost of pitch to provide a high top
speed on a fast boat, need lots of low down torque to get them away
quickly from a standing start. What you really want is an engine with
the best low down torque & traditionally 4 strokes have been good at
this, however this is not the case with the new 4 stroke OBs.

It's true 4 strokes can produce good torque however in your hole shot
premises a 2 stroke can be just as good & sometimes better (more bangs
for a given number of prop turns). So the 2 strokes can produce good low
down torque which means they can bog less from a standing start, this is
usually put down to their weight advantage but.

The new 4 strokes are usually very high revving engines (sometimes
higher than the equivalent HP 2 stroke) which means they produce their
best torque quite high up the rev band, again contrary to the usual
comments.

For getting away quickly the 2 strokes are OK indeed that's probably
their only strong point, but for fuel economy, long service life, ease
of use, resale value etc the 4 stroke is the go.

You've been warned about the Evinrudes, stay well away for the next 5
yrs at least, indeed I'll predict they won't even exist in 5 yrs just as
I did Ficht & it only took 3 yrs for them to go:-).


K

For getting away quickly the 2 strokes are OK indeed that's probably
their only strong point, but for fuel economy, long service life,

Large 2 stroke OB's have demonstrated their ability to provide a long
reliable service life over several decades, large 4 stroke OB's have not.

/nods

I know of *many* two-stoke outboards that have several decades on individual
units.

If the 4 stroke outboards turn out anything like the 4 stroke motorcycle
engines. They won't have as long a service life.

-W

"-v-" wrote in message
...
For getting away quickly the 2 strokes are OK indeed that's probably
their only strong point, but for fuel economy, long service life,

Large 2 stroke OB's have demonstrated their ability to provide a long
reliable service life over several decades, large 4 stroke OB's have not.

Clams Canino wrote:
/nods

I know of *many* two-stoke outboards that have several decades on individual
units.

If the 4 stroke outboards turn out anything like the 4 stroke motorcycle
engines. They won't have as long a service life.

-W

"-v-" wrote in message
...

For getting away quickly the 2 strokes are OK indeed that's probably
their only strong point, but for fuel economy, long service life,

Large 2 stroke OB's have demonstrated their ability to provide a long
reliable service life over several decades, large 4 stroke OB's have not.






Touche!!! Point taken from you both & begrudgingly accepted:-)


K

So...if you want to play with TC-3 oil, snort oil fumes, sacrifice
fuel mileage, and endure the noise for a superior hole shot, the 27 to
3 vote is probably right on target. You'll be much happier with the 2
stroke.

I don't get it, but different strokes for different folks.....

--



Grady-White Gulfstream, out of Southport, NC.

http://myworkshop.idleplay.net/cavern/ Homepage
http://www.southharbourvillage.com/directions.asp Where Southport,NC
is located.
http://www.southharbourvillage.com/autoupdater.htm Real Time Pictures at
My Marina
http://www.thebayguide.com/rec.boats Rec.boats at
Lee Yeaton's Bayguide










Everyone in the marine industry and most of its environmental critics are aware
that there are now at least four manufacturers of two-cycle outboards with DFI,
direct fuel injection: systems that put the fuel directly into the combustion
chamber after the intake and exhaust ports close. Such systems eliminate loss
of some of the incoming fuel charge out the exhaust ports along with the
scavenged products of combustion that occurs with carbureted or EFI manifold
injection systems. Nevertheless, conventional wisdom tells most of the critics
of the two-cycle engine that it will never be as clean as a four-cycle engine.
For this reason they would eventually advocate banning the two-cycle engine
from the waterways on environmental protection grounds.

There are even more manufacturers producing four-cycle outboards, including the
same manufacturers that make the DFI two-cycle engines. They must seemingly
follow down both roads for self preservation, as part of the outboard market is
definitely leaning in the four-cycle direction, driven that way by hype,
environmental concerns, and certain perceived advantages. We have already
considered the ramifications of the increased engine weight for the
four-cycles, the potential effect on boat trim, and the possible inability to
float the boat level when swamped, as required by federal regulations for
outboard boats less than 20-feet long. Then there is also the increased cost
and complexity involved with four-cycle power, to be offset by savings realized
in fuel consumed and elimination of smoke and oil slicks.

This may be the price of progress, they say. But, is it possible to "have your
cake and eat it, too?" Some recent tests run comparing 2002 model two-cycle DFI
outboards with four-cycle outboards of equal power rating, mounted on the same
boat, would seem to indicate such things are really possible. Comparison tests
of two brands of four-cycle 225-hp outboards were made with a current state-of
the-art DFI two-cycle 225. On identical 20'7" boats one four-cycle brand
produced a best mileage of 4.7 mpg at 27.7 mph while the two-cycle gave a best
4.5 mpg at 28.6 mph. Very close. But, the two-cycle had a top speed of 59.8 mph
against 52.4 mph for the four-cycle. At the same 52-mph speed the two-cycle
gave better mileage to the tune of 3.2 mpg to 2.7 mpg for the four-cycle. The
two-cycle produced better fuel mileage at every speed from 34 mph up and was
also better at trolling speeds of 4-7 mph.

When tested against the other 225-hp, four-cycle brand on identical 24' boats,
the DFI two-cycle again prevailed overall, delivering a matching best 3.15 mpg
at 32 mph. This outran the four-cycle 49.3 to 45.7 mph, getting better mileage
(2.58 mpg) at its top speed than the four-cycle (2.44 mpg) at its top speed. It
also produced far better mileage in the trolling speed range from 3.5-8 mph.

A third set of tests compared a 135-hp, two-cycle DFI outboard against a
130-hp, four-cycle outboard on identical 20' boats. The two-cycle delivered
4.25 mpg at 20.8 mph against a best 3.97 mpg at 20.4 mph for the four-cycle.
Best economy for the two-cycle was achieved at 27.9 mph: 4.45 mpg. It also
bested the four-cycle in the 3-8 mph trolling speed range and beat it in top
speed 43 mph/3.54 mpg to 37 mph/2.97 mpg.

"Bah, humbug!" you might say. But there are sound engineering internal
combustion engine principles for this surprising result. It is true that the
typical four-cycle engine may have an inherent advantage in fuel consumed per
horsepower. But not when the engine must be designed to produce very high
horsepower per cubic inch of displacement at high engine speeds, as it must to
achieve even the already heavier weight seen when compared to its two-cycle
competitor.

In order to achieve this high-power output, while firing only every other
revolution of the crankshaft, the camshaft valve timing must develop
considerable overlap between intake and exhaust valve openings and closings,
which means it begins to suffer some of the same raw fuel loss out the exhaust
problems as the carbureted or manifold injected two-cycle engine. It only has
manifold injection, so the fuel and air must mix in the manifold and enter
together past the intake valve into the combustion chamber while the exhaust
valve is still partly open. The result is Some loss in fuel economy.

Since the four-cycle engine has the same radical valve timing at low engine
speeds, it suffers even more when compared to the two-cycle DFI engine at
trolling speeds. The only way to fix this problem in the four-cycle engine is
to go to direct fuel injection into the combustion chamber after the valves
close, like the DFI two-cycle, or have a system providing variable valve timing
with engine speed, conservative timing at lower speed and radical timing at
higher speed. Such systems are now being developed for future automobile
engines. Such things would add complexity, cost and weight, to an already more
expensive and heavier product.

Then there is the factor of acceleration from idle to planing speed. On the 241
boat the 225-hp, two-cycle DFI went from zero to 150 feet in 7.06 seconds while
the four-cycle took 7.76 seconds. On the 20' boat the 135-hp, two-cycle DFI
went zero to 150 feet in 6.2 seconds while the four-cycle took 8.7 seconds for
the same distance. Acceleration from zero to 30 mph on the 20'7" boat for the
225-hp two-cycle DFI took 5.77 seconds compared to 10.7 seconds for the 225-hp
four cycle. This demonstrates the better low-end torque and fast-rising power
curve of the two-cycle, firing every revolution of the crankshaft. The
four-cycles are quieter at low engine speeds, but this advantage goes away at
the higher engine speeds.

So, the conclusions are that the state of the art two-cycle DFI outboard can
match or beat the four-cycle in fuel economy, top speed, and acceleration. What
about exhaust emissions, which brought on the whole move to four-cycle
outboards in the first place? These two-cycle engines can match or beat the
four-cycles there, as well. It matches pretty much with the fuel economy story.
The more fuel the engine consumes at a given boat speed, the more exhaust
emissions that come out the other end. With precise microprocessor control and
direct injection of the fuel into the combustion chamber after the ports close,
the two-cycle DFI can better the most stringent exhaust emission requirements
now proposed out to 2007. The four-cycle can do no better.

After more than five years of testing and field experience the 2002 two-cycle
DFI outboards have been developed to have quality durability, economy and
environmental friendliness to match or beat the four-cycles, and at lower
weight and cost. Both can exist and be successful in the marine market but no
one should sell the two-cycle engine short on its ability to survive and
prosper long into the future. It just has too many good things going for it.
You might even see it on some future stern drives.

Ralph Lambrecht is an engineer with more than 50 years of experience in the
marine industry and marine safety standards development.

Lambrecht, Ralph. 2002. “Two-stroke conventional wisdom.� Boat & Motor
Dealer. April. 34-37

Gene Kearns wrote:

In my own limited experience, I traded two 2-stoke Yamahas for two
4-stroke Suzukis and, thus far, they have proved much quieter, easier
to crank, and more fuel efficient (at the speeds I use). Plus, I
don't have to screw around with that crappy 2-stroke oil or have to
breathe its noxious fumes in an unfavorable wind.

Personally, I'll take the 4-strokes any day..... but then, they fit
my usage pattern.


Though the 1990s and up until this year, we had a series of Merc
two-cycle outboards, 90, 115, 135 Opti, on different boats. Since each
had a decent-sized oil bottle (the 90 and 115 under the hood, so to
speak), messing with the oil was not a real annoyance. The 90 seemed to
spew out more of an oil smell and smoke at trolling speeds than the 115,
but the Opti was a good-neighbor engine...no visible smoke, no smell.

Our Yamaha 225 four-stroke idles much more quietly than any of the
Mercs, and it is one smooth-running engine. I see where Yamaha has
bounced its 250 HDPI up to 300 horse. I'm sure in a few years Yamaha
will have a 300 hp four stroke and at that point, I'll trade in the 225,
for the 75 additional horses. Maybe.

So far, I have no complaints about teh 225 Yamaha.


--
Email sent to is never read.

"K Smith" wrote in message
...
Clams Canino wrote:
/nods

I know of *many* two-stoke outboards that have several decades on
individual
units.

If the 4 stroke outboards turn out anything like the 4 stroke
motorcycle
engines. They won't have as long a service life.

-W

"-v-" wrote in message
...

For getting away quickly the 2 strokes are OK indeed that's
probably
their only strong point, but for fuel economy, long service life,

Large 2 stroke OB's have demonstrated their ability to provide a
long
reliable service life over several decades, large 4 stroke OB's have
not.






Touche!!! Point taken from you both & begrudgingly accepted:-)


K

You might want to check out the Bass and Walleye boats page to see if
they have any comparisons on line. And keep in mind that it won't be
long and you won't be able to buy (new anyway) any of those fine
carburated 2 strokes that have demonstrated reliability, only 4 strokes
or DFI. Now which of those have the best reliabilty. And I don't know
where you got the idea that 2 stroke MC engines were more durable than 4
strokes.

del cecchi