I always heard that when you stroke an engine you are getting greater torque gains than anything else. Then i had some guys tell me that you get more horsepower by stroking your engine and more torque by boring it over. Which is correct?
An engine is a pretty much just a big vacuumn boring increases the vacuums strength...the stroke creates more torque...think of stroking in terms of this, when you are trying to get a bolt loose and you cant with a regular ratchet, but when you throw a cheater bar over the ratchet it allows you to apply more torque with less effort, a bad analogy but stroking a motor does the same thing via longer stroke....
Horsepower is derived from torque (with respect to rpm). So yes, when you increase piston speed (have a longer stroke) you get more torque AND horsepower. When you have a shorter stroke but a bigger bore, you can still stuff more air in the chambers but an engine like this has to find its power in the higher rpm range due to the shorter duration of the effective power stroke in the 4 cycle process. Engines like this can have more horsepower due to running such rpms, but they must rev higher to get the overall effective kind of power output with comparrison to an engine that doesn't have to rev as high (due to a longer stroke).
Imagine that the crank is a lever. The longer you make a lever from its pivot point, the more it multiplies force. However, you must move the end of the lever faster to do the work in the same amount of time. That is a very simplified explanation of a complex subject...