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Rod stroke ratio comparison Formula 1 and NASCAR Cup motors

JEAN GENIBREL


NASCAR and FORMULA 1 ROD STROKE RATIO & PISTON SPEED

 

It is pointless to address the length of the connecting rod in any engine, racing or otherwise, without looking into the ratio of the length of the rod to the crankshaft stroke.

We can calculate the rod stroke ratio (RSR) by dividing the rod length by the stroke value. What is more, the piston pin location in the piston also affects the result of the calculations. Moving the pin closer to the thrust side causes the piston to acquire shorter rod characteristics. Conversely, when we move the pin toward the non-thrust side of the bore it makes the rod act longer. Using the rod/stroke calculator and piston pin location calculator along with a personal computer based engine development software can unlock a plethora of ideas and results that we can use to improve performance, increase BMEP, torque, power endurance, and reliability.


 

At 18000 RPM Formula One engines with an RSR of 2.56 achieve peak piston speeds of over 7000 feet-per-minute (FPM).  A NASCAR Cup engine piston speed reaches 8800 FPM at 10000RPM with an RSR of 1.91.The F1 numbers are due mainly to the engines’ short strokes.

 

 

 

At piston speeds above 5000 FPM, the pistons must be equipped with forced pin oiling slots to cool the pins, the rings, and the pistons. This load increases at the square of the speed, and at higher speeds, the rings, pistons, and pins receive less lubrication from the spinning crankshaft. Reduced oiling can result in overheated piston tops and skirts as well as the rings and pins.

 



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