Rod McInnis" wrote in message
...

"Lawrence James" wrote in message
nk.net...

50hp is 50hp.

Not exactly.

What gets you moving is torque. Horsepower is torque times RPM.

In many cases, a two cycle engine is capable of running at a higher RPM.
If
you can get 10% more RPM out of an engine, you can often get 10% more
horsepower. That doesn't mean you can use that horsepower. If you can't
get the engine up to that extra 10% it will never be used. Unfortunately,
it was at that higher RPM where the engine earned its rating.

If there is a concern about getting on plane, then low end torque is king.
This is where 4 cycles usually have the advantage over two cycles. On the
other hand, if you can get planing okay, and need the best top end, 2
cycles
usually come alive at the higher RPMs and can provide more top end.

Rod McInnis





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.

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.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. A cam built for
low end torque will suffer at high rpms while a cam built for speed will suffer
at low rpms. Marine four strokes are not cam'ed for low end since they are
mostly used at the higher end of the rpm band.

Two strokes generally have a much flatter torque curve.

Be very careful believing everything you read here, you may end up sorely
disappointed if you buy a four stroke. They are heavier and produce much less
low end torque. The four strokes are selling based on their fuel economy and
emissions, not on performance.

Barry