Q: What is rod ratio?
How is it calculated?
Use the following formula to calculate rod ratio:
Rod Length ÷ Stroke Length = Rod Ratio
For example, a stock small block Chevy 350 has 5.7 in. connecting rods and a 3.48 in. stroke:
5.7 in. ÷ 3.48 in. = 1.64 Rod Ratio
How does it affect performance?
Rod ratio can result in a little more power or a slightly longer piston ring life.
Typically, only high-performance engine builders make adjustments to rod ratios. There are many other factors that have much larger effects on engine performance.
|Lower Ratio||Higher Ratio|
|More wear, vibration, and heat||Less friction, wear, and heat|
|Shorter engine block deck height||Holds compression, improves combustion efficiency|
|More vacuum at low rpm||Less vacuum at low rpm|
|Better throttle response||Poor throttle response|
|More low-end torque||Less low-end torque|
|Common in daily drivers and street performance||Common in race engines|