engine design theory question: over square vs under

Ring and cylinder bore wear are related to how far the piston travels. Also, the SPEED that the piston moves is a factor in piston ring wear. Excessive speed causes high acceleration and bouncing of rings.

Now, we can get a given displacement by having a long stroke, tiny bore, tiny stroke and big bore, or a balance (equal bore and stroke). The longer the bore, the faster and further the piston travels each revolution, so long bore engines are not good for longevity unless they are very slow turning (which is not good for power).

Also, the bigger the bore, the more area we can have in valve heads. Small bores relative to stroke make it hard to cram in big valves. Many racing engines through the years have gone to extremes on oversquare (bore bigger than stroke.

keep in mind that long stroke engines, while lower revving, also tend to produce more torque because of the longer moment arm of the crank throw. So you win some and you lose some.

nate

This makes sense since the 4 banger will need a fighting chance at low- end since it has 2 less power strokes per revolution.

2 less power strokes than... what? A V-8? Yes. (Remember it's one power stroke per *two* revolutions for the 4-stroke ICE.)

both have advantages and disadvantages

short stroke allows more valve space good for hi power allows slower piston speed allows you higher rpm = more power allows lower crank stress = more rpm = more power greater heat loss throught larger piston =less efficency allows shorter hight of engine but engine becomes longer

long stroke more efficiecnt combustion less heat loss greater pistion speeds so this engine is suited to low rpm and low rpm engine can run more efficiently