[quote
Small valves make better torque, larger valves make better hp.
Undersquare engine's smaller bores don't have room for large valves. If an oversquare engine is given small valves, it too makes higher torque.
Cam duration plays a big part, too. Short duration makes good torque at low rpm, long duration makes good hp at high rpm.
It's not the stroke, and I'm not pulling this out of my butt. It's from an old TDC article.
Well your both right. There is more to it. Putting smaller valves, or less valves in a short stroke will increase torque, but the peak will be at a higher rpm than a similar displacement long stroke motor. Putting larger or more valves on a long stroke will increase hp and rpms but again less so then a similar displacement short stroke. In the end the short stroke is capable of higher rpms and peak hp simply because the pistons have a shorter distance to travel and there is room for more aggressive valving. But it is not capable of attaining the very low rpm peak torque numbers of a long stroke.
