ROD/STROKE-DWELL-ROD ANGLE & PISTON SPEED CALCULATOR from APPLIEDSPEED.COM
Smokey Yunick was very much an advocate of longer rods in racing engines. In fact, he often said that any engine would run better with the longest rods with which it could be fitted. Smokey was not known for being wrong very often, but there are times when one could say: “Yes, but.” Moreover, this is one of them.
The connecting rod to stroke ratio has a marked effect on the angle at which the rod angles in relationship to the bore center line. The severity of this effect increases as the rod shortens. Longer rods have a reduced effect on piston side loading than do shorter rods. See the APPLIEDSPEED.COM rod/stroke calculator .
The rod stroke ratio and the piston pin offset affect several engine dynamics, including piston speed and acceleration, piston dwell at top dead center and bottom dead center, piston side loads, cylinder loading and bearing loads. Many of these elements play roles in engine aspiration, combustion, and wear.
With the rod stroke ratio and pin offset calculator click here it is possible to calculate piston position, velocity, acceleration, piston motion, differences between several ratios, TDC and BDC, a sensitivity plot and sensitivity graphs.
NASCAR and Formula 1 engines show marked differences in their rod to stroke ratios, engine speeds, and power output.
When various rod, stroke, and pin offset parameters are entered in a modern engine calculator software, it becomes possible to compute new camshaft events, different compression ratios, various exhaust tube areas and lengths, and ignition timing. What is more, the operator can observe how various rod /stroke ratios affect the torque and power peaks to suit specific application requirements.
The connecting rod to stroke ratio has a marked effect on the angle at which the rod angles in relationship to the bore center line. The severity of this effect increases as the rod is shortened, Line on the left image indicates the direction of piston side load as the piston rises in the bore. Longer rods have a diminished effect on piston side loading than do shorter rods.
The piston pin offset can be an interesting approach when rules do not permit different length rods. Offsetting the wrist pin in the piston has the same effect as lengthening or shortening the rod. Adjustments in piston compression height must be addressed to maintain the original compression ratio and to prevent piston contact with the head.
Shorter rods yield a lower block deck height which saves weight and permits improved aerodynamics from lowered hood heights. Long rods in alcohol motors have been found to cause detonation due to the long dwell time.
Resources: http://www.epi-eng.com/piston_engine_technology/comparison_of_cup_to_f1.htm. click here
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