The thing that keeps coming up is the 'square,' 'over-square,' 'under-square,' terms. It is as if proportion has something to do with it, and not relative stroke length - in this case, they remain the same for the F and 2F.
Don't over-think this, it's just one way of identifying a "stroker" motor. Square motors are just where the diameter of the cylinder bore equals the length of the stroke. Over-square motors have a bigger cylinder diameter than the length of the stroke; as previously discussed, this yields lower piston speed and hence enables more rpm and hence more hp. Under-square (or "stroker") motors have the cylinder bore smaller than the stroke length. As has been said, longer stroke = more leverage of the pistons and con rods on the crankshaft, thus more torque, but with the resultant faster piston speed it limits rpm.
Hoping that some carb gurus can shed some light regarding the 'undersquare' proportion and how it might affect carburetor design.
I'm no carb guru, but I've built more than a few (but mostly motorcycle) motors including stroker motors in my day.
Under-square designs are used to rev high. high-revving motors need very efficient intake, valves, and exhaust systems, hence the development of overhead cams, efficient squish-design combustion chambers, multiple valves per cylinder, and modern fuel injection systems. Carbs are too much of a compromise and can't be efficient at all rpm's, they can only be efficient in a relatively narrow rpm and volumetric range. Carb designers tried to address this over the years by going from single-barrel large venturi carbs to two smaller venturi barrels, then to four even smaller (relatively) venturis. But they were never as efficient as a good FI system.
I hear folks talk about a 'tractor,' quite a bit, but what does that imply?
A farm tractor has some similar design goals to a 4WD off-road truck, namely high torque at slow steady speed and low to moderate rpm. Both have used stroker motors, heavy flywheels, and low gearing to accomplish this. Both were originally reliable and repairable in the field with commonly-available tools. Horsepower, highway speed, and efficiency were much less important considerations. The F and 2F motors are good examples of this, hence the comparison to tractor motors.
