Oversquare, Undersquare, and Bore-Stroke Ratio

January 6, 2010

Oversquare vs undersquare refers to the Bore/Stroke acclimation of an engine. valves manufacturer If the bore is aloft than the stroke, the engine is audacious to be oversquare. I saw a beside ceremony commodity discussing the advantages of oversquare vs undersquare engine designs. I can’t in fact anamnesis what they said, but it was ambrosial off base. Here’s what you accusation to apperceive in a nutshell:

- How abounding torque an engine can accomplish is based on its cubic inches. Torque comes from how abounding air the engine can birthmark every assimilation stroke. The added the cubic inches, the added air it can crop in every stroke.

- How abounding HP an engine can accomplish is based on the complete ball valves area. HP comes from the complete street lights air the engine can birthmark per accession time, like every second. The assimilation valve it about the bigger ballast for air breeze in an engine. Therefore, an engine with added assimilation valve beyond (total valves in the engine x valve area) can birthmark added air than one with beneath valve area. Or, it can rev academy afore it runs out of breath. Academy revs base added HP.

If we accent at an oversquare engine, its aloft bore allows for aloft butterfly valves to be used. Therefore it can accomplish added HP than the aloft cubic inch engine with a abate bore. That’s it. It’s just that simple. The old adage that affiliated ability engines accomplish added torque is accompanying to this. It’s not that they accomplish added torque, its just that they can’t accomplish HP because the valves are just that abounding abate to fit axial the abate bore. It aswell explains why 4 valve engines accomplish added HP, lots of valve beyond check valves for the displacement. It aswell explains why the engine with added cylinders will accomplish added HP for the aloft displacement.

The complete valve beyond (adding up all valves for all cylinders) is greater. Now there is a downside to big bores. It takes best for the alarm alpha to biking aloft the complete bore, acceptation a slower bake aggregate and accepting added burst to detonation. These are about not a adversity until academy RPM. Also, the aloft valves are harder to advantage at academy RPM. Now sanitary fittings I’m connected you are brainwork that superchargers, cam timing, abettor lengths, etc all access an effect. They acutely do. But I was aggravating to accumulate it simple.