You understand that a 2 stroke has to intake a charge of air and gas,
compress it, ignite it, and get the results out of the cylinder on one up
stroke and one down stroke? To do that it has to have a considerable
overlap of those items. That's why a 2 stroke is not twice as powerful as
the same sized 4 stroke, even though a 2 stroke fires every stroke it wastes
some of the power stroke with early exhaust and can not load the complete
cylinder displacement with a fuel/air charge. That also creates the
situation where at parts of the rpm range you are either letting the burning
fuel out before it has completed or letting unburned fuel run out before you
close the exhaust port. A really high performing 2 stroke is peaky, it has
a small rpm range where it runs like hell, anything over or under and it's a
dog. That rpm range is where the port openings and the flow is just right
to get rid of the exhaust and the scavaging effect loads the maximum charge.
If you close up the overlap then you reduce the power stroke so much that
you can't even get half the power of a 4 stroke power cycle.

Plus adding other stuff like valves and compressors negates the main
advantage of the two stroke, it's simple and has few moving parts.

"HLAviation" wrote in message
link.net...
Why not?

"JamesgangNC" wrote in message
ink.net...
Unfortunately no it doesn't.

"HLAviation" wrote in message
ink.net...
An exhaust valve solves that problem.

"JamesgangNC" wrote in message
ink.net...
Because that doesn't address the burn problem. 2 strokes do not
burn
clean
because the intake and exhaust all happens at the same time. Over a
wide
rpm range you invariably have fuel that escapes with the exhaust.
That's
the problem they're trying to solve because they have to meet
emission
standards now.

"HLAviation" wrote in message
link.net...
Ya know, a 2 stroke doesn't have to oil the bottom end through the
fuel.
I've always wondered why the OB manufacturers didn't change the
design
to
a
closed crankcase design with a dry sump oil system and a simple
supercharger. Cheaper, simpler, proven.

"Calif Bill" wrote in message
k.net...

"Harry Krause" wrote in message
...
JamesgangNC wrote:
Not taking a position on Karen's usefulness but I have to
agree
with
her
position on 2 strokes. There is just far too much
established
4
stroke
engineering that can be used to make reliable riskfree 4
stroke
products.
Trying to make a 2 stroke low emission is just not worth it.
Doing
so
negates one of the biggests advantages of a two stroke, it's
simplicity.

Do you have some legitimate statistics that demonstrate that
four
stroke
outboards are measurably more reliable and riskfree than
two-stroke
outboards. I mean generally, say, for the last 50 years of
production,
in horsepowers of 150 or more. Big, highly stressed engine.
The
real
deals.

I'll be glad to read them with great interest.

Not opinions. Genuine, scientifically based statistics.


--
A vote for Nader is a vote for Bush;
A vote for Bush is a vote for Apocalypse.

50 years is too far back. Those 2 strokes were simple. The
Optimax
and
Ficht of the last 10 years have not shown a lot of reliability.
Witness
the
demise of original OMC. With the big Honda a basic high
performance
car
engine with a dry sump. there should be great reliability. The
E-Tec,
etc,
with the addition of air compressors, low amount of lubrication
at
the
lower
end as the requirements for less oil and emissions. Makes for a
engine
that
is on the edge of reliability.
Bill