Well let me explain why
Ratio "n" = Rod Length ÷ Stroke
The rod’s length is measured (for this purpose) from the center of the piston-pin opening to the center of the big-end bore, not overall. There is a small range of ratios for most conventional piston engines: the rod is between roughly 1.4 and 2.2 times the stroke length. It’s not possible for the rod to be the same length as the stroke, and rods much longer than twice the stroke make the motor very tall, and are not practical for most purposes (although used for racing).
The rod angle must not encourage excessive friction at the cylinder wall and piston skirt. A greater angle (smaller value of "n") will occur by installing a shorter rod or by increasing the stroke. A reduced angle (larger value of "n") will occur with a longer rod or a shorter stroke.
If the rod length is decreased, or the stroke is increased, the "n" ratio value becomes smaller. This has several effects. The most obvious is the mechanical effect. Motors with low values of "n" (proportionately short rods or long strokes) typically exhibit the following characteristics (compared to high "n" motors): physically shorter top-to-bottom & left-to-right (more
oil pan, header, and air cleaner clearance) lower block weight (400 vs. 440, for example) higher level of vibration, shorter pistons, measured from the pin center to the bottom of the skirt. Greater wear on piston skirts and cylinder walls. Slightly higher operating temperature &
oil temperature due to friction
There are also differences in how the motor breathes: intake vacuum rises sooner ATDC, allowing bigger carburetors or intake port runner & plenum volumes to be used without loss of response
on the negative side, a small or badly designed port will "run out of breath" sooner. Piston motion away from BDC is slower, trapping a higher percentage of cylinder volume, making the motor less sensitive to late intake valve closing (hot cams)
Spark advance is also affected: earlier timing (more advance) is required, as the chamber volume is larger (piston is farther from TDC) at the same point of rotation. The motor may also be less knock-sensitive, as the chamber volume increases more rapidly ATDC, lowering combustion pressure (this is useful for nitrous & supercharged motors)
Threaded Mode
