ROD/STROKE-DWELL-ROD ANGLE & PISTON SPEED CALCULATOR from APPLIEDSPEED.COM

ROD/STROKE-DWELL-ROD ANGLE & PISTON SPEED CALCULATOR from APPLIEDSPEED.COM

 

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.” And this is one of those times.

 

 

Effects of The Rod to Stroke Ratio

The connecting rod to stroke ratio and the piston pin offset have a marked effect on the angle of the rod 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. Longer rod to stroke ratios have their drawbacks.

AppliedSpeed.com has created a rod/stroke ratio calculator. The main reason to use the calculator is to calculate a rod length or a piston pin offset value when changing the crank stroke. Another time the calculator comes in handy is the see the location of the piston in the bore when identifying a camshaft.

The APPLIEDSPEED.COM  rod/stroke calculator  can help in determining the load and dwell time of the pistons as well as the piston position during a stroke, and this can affect the power curve and it may necessitate experimenting with different camshafts.

The main objection that engine builders have to lengthening the rod length is that a long rod dwells longer at TDC and it dwells less at BDC. The increased dwell at TDC can cause detonation and as one major engine builder had told me: "The piston does not do any work if it dwells at TDC for long and at BDC it increases the load by returning suddenly to the upward stroke."

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 calculatoclick 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. Image: http://www.epi-eng.com/piston_engine_technology/comparison_of_cup_to_f1.htm

 

 

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

 

APPLIEDSPEED.COM is the website that sells performance and racing cooling parts for all disciplines of racing. From circle track to road racing, autocross, off-road racing, drag racing. Also, appliedspeed.com addresses the needs of racers who tow their race cars to the track with cooling products for their tow vehicles with products such as oil coolers for engines, transmissions, power steering and differentials. Also serviced include motor-homes, industrial engines, and Jeeps.

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