Low end torque - 4 stroke vs. 2 stroke

[jason555]

I have a 300 Suzuke on my 23 CC turning a 16 by 20 three blade wheel. Most noticeable difference for me is the boats ability to stay on plane at just about any speed in any water/wind/wave combination condition.

[Fr. Frank]

Crudely illustrated, the difference is not whether it's 2-stroke or 4-stroke. The difference is the torque curve and horsepower "powerband".

For example, if a 225 hp motor only develops the torque to reach 75% of the full 225 hp between 3500 and 4000 rpms, then below 4K it will perform like it's only developing 170 hp or less.

On the other hand, a motor which has the torque to spin up to say 90% of it's rated horsepower at only 3000 rpms, then at 3K it's developing over 200 hp already. Both motors may develop a true 225 hp at the top of their respective powerbands.

Take Mercury Verados. A 225 hp rated Verado develops its max hp (238 hp) at 5800 rpms. (It actually makes more at even higher rpms, but the torque curve falls off) It has a very flat torque curve, thanks to the supercharger. Mercury doen't reveal the maximum torque developed, just the shape ot the curve. So that same 225 motor is already developing over 200 hp at only 2650 rpms, giving it tremendous acceleration potential. It's greatest drawback is its weight.

Contrast that with the old OMC 90* V6 225. While it also developed 230 hp at the top of it's powerband, it didn't break the 200 hp mark until the motor was turning 4100 rpms.
I don't know how much the max torque developed was, but the torque curve is much steeper, not achieving 75% of torque until above 3000 rpms.

Not just horsepower, ladies and gentlemen, but the torque to develop and apply it when you need it.

And just for the record, the Etec is supposed to develop about as much torque as the Verado, although with a bit steeper torque curve.