Square Bore and Stroke: Less Vibration?

[nicholastanguma]

Years ago S&S offered a vtwin called the SS100; like all engines of its 45 degree kind it had no counterbalancer but was still a performance unit, so the square bore and stroke were used to find the "ideal" ground between torque and horsepower and vibration. Reviews of the time reported the engine to indeed be very powerful all through the rev range while creating less vibration than undersquare or oversquare configurations--but only up to a point. Frustratingly, specifics were not to be expounded upon.

So now I'm wondering if, since a 45 degree vtwin is inherently very vibrational, a square bore and stroke would also produce fewer vibrations in other inherently vibrational engine types such as the thumper and the inline four?

 

[85_Ranger4x4]

More cylinders run smoother.

 

[b dkw1]

Square B&S motor is hard to do on a 45* motor. Your pistons want to run into each other at the bottom of the stroke unless you have really long rods. With this comes a very low rod ratio and your ports have to be sized to reflect that. Easier to make good power from a 90* motor like a Ducati. Also easier to balance.......

 

[Buliwyf]

My Ducati will blur your vision if you lug it in too high of a gear. Waaaaaaay oversquare. It smooths out with rpm just fine though.

You're going to see oversquare truck and car engines more often now. Thanks to modern transmissions, we don't need stroke to make torque anymore. They should be very smooth.

 

[85_Ranger4x4]

You're going to see oversquare truck and car engines more often now. Thanks to modern transmissions, we don't need stroke to make torque anymore. They should be very smooth.

Thanks to modern engine tech short stroke small displacement engines can have good low end torque. Couple that with a good trans and you really have something.