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Port Timing Duration Calculator

Required Data Entry
Measured Stroke
Connecting Rod Length
Port Height Above BDC

Calculated Results
Open Duration Degrees
Updated: 7/31/11

This calculator requires the use of Javascript enabled and capable browsers. This script calculates the approximate two cycle engine timing duration for the open port. Data can be input and calculated in any designation so long as it is consistent. Enter the values for stroke, connecting rod length and port height (piston above BDC). Click on Calculate. The resulting calculation is in degrees in either metric or US entered and designated values.

For purposes of OUR calculator, we define Duration as the number of degrees of crankshaft rotation that a port is open. Port timing is the degrees of crankshaft rotation after TDC to where port starts to open. Top Dead Center (TDC) is the top of the piston's stroke and Bottom Dead Center (BDC) is the bottom of the piston's stroke. A Port is an airway or duct that is cast or machined into the cylinder. The Crank Angle is the crankshaft rotation measured in degrees. There are 360 degrees total.

Obviously, this is a very close approximation due to small inaccuracies on variable data input. Also please see our Port Height Above BDC Timing Calculator for two cycle engines and our Timing Mark Calculator for all engines.

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