"F330 GT" wrote in message
...


Two stroke engines have always made more low end torque, both motorcycle
and
marine. For one reason because the spark plug fires every revolution
instead of
every other.

If you compare engines based on displacement, what you say is true. If you
compare based on rated horsepower, it will be just the opposite. For a
given horsepower, a 4 cycle engine will have a lot more displacement to make
up for the extra two cycles it has to go through before getting to a power
stroke.


Engine horsepower is rated at the point of the torque curve where the hp
(torque x rpm) is the highest. Not at the maximum rpm. The torque (and
therefore the hp) ususally falls off very quickly at high rpms.

This is true.

The grind of the
cam on a four stroke controls the torque curve and the maufacturer can
move the
maximum torque up or down the band based on duration and lift.

If you consider destroying the low end torque so that you can have a lesser
peak at a higher RPM "moving the maximum" then I suppose this can be
considered correct.

A cam built for
low end torque will suffer at high rpms while a cam built for speed will
suffer
at low rpms.

This is a simplification of a much more complicated thing. The reason that
torque falls off at higher RPM is because the engine can't breath. One way
of getting the engine to breath better is to open the valves sooner, wider
and faster. It is the "sooner" part of that process that screws up low end.
It is usually the rate that the valves can open and close that limits the
upper RPM limit of a four stroke.


Marine four strokes are not cam'ed for low end since they are
mostly used at the higher end of the rpm band.

I doubt that. When you mess up the low end, you also mess up the idle
characteristics, which is important to most marine applications.


Two strokes generally have a much flatter torque curve.


???? What two stroke torque curve have you been looking at?

Find anyone who has ridden a two cycle motorcyle and ask them about the
acceleration at low RPMs vs being "on the pipe".

A conventional two stroke engine relies on the downstroke of the piston to
pressurize the crankcase to force the air/fuel mixture around the piston
into the cylinder. Reed valves are generally employed to prevent the
air/fuel mixture from backflowing through the carburator. At lower RPMs,
the reed valves are not as effective and the cylinder doesn't scavage as
well. As the RPMs increase, the exhaust momentum will actually help
scavange the cylinder and the engine "comes alive". In many cases, a 2
cycle is just coming to life at an RPM where a 4 cycle is starting to fall
flat.

Rod