Hittade lite angående detta:
"The ratio of rod length to stroke length (usually represented by the symbol “n” ) is almost always between 2.1:1 on the “long” end, and 1.4:1 on the “short” end. 99% of all motors fall between these 2 extreme limits, with most standard production designs between 2.0:1 and 1.45:1.
An “n” value of 1.75 is considered “ideal” by some respected engine builders, if the breathing is optimized for the design. Except for purpose-built racing engines, most other projects are compromises where 1.75 may not produce the best results.
The percentage of mixture captured, compressed, and burned in the cylinder at a specific point of intake valve closure partially depends on the motor’s rod ratio. The piston’s motion during crankshaft rotation is not symmetrical: the piston speed before & after TDC is faster than before & after BDC, but the difference is not constant - it varies with the rod ratio. Two motors with the same stroke, but different rod lengths, will not have the piston in the same place at the same point of crankshaft rotation. The only 2 exceptions are 0° (TDC) where both strokes are zero, and 180° (BDC) where both strokes are equal & nominal.
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A better method of calculating maximum RPM is based on the point of fastest piston acceleration, and takes into account the rod length (longer rods improve the safe RPM slightly). The formula is:
Z = N2 × S (1 + (1 ÷ 2n)) ÷ 2189
where “Z” is piston acceleration in feet per second, per second, “N” is engine RPM, “S” is the stroke length in inches, “n” is the rod-to-stroke ratio (as described, supra), and 2189 is a constant. A safe limit for “Z” is about 100,000 f/s2, although this will cause ring flutter with 1/16” compression rings.
Long-rod motors (“n” = 1.75 to 2.1:1) will have the piston closer to TDC than the short-rod motor at any point between 90° BTDC & 90° ATDC. Short-rod motors (“n” = 1.4 to 1.75:1) will have the piston closer to BDC than the long-rod motor at any point between 90° BBDC & 90° ABDC.
Short-rod motors have slower piston movement upwards away from BDC on the compression stroke, and will capture more mixture at the same point of intake valve closure. This makes them more tolerant of extended (late intake closure) cam timing. "
http://victorylibrary.com/mopar/cam-tech-c.htm
Nu från bilsidan men funktion är samma.
