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Old 01-07-2006, 09:06 AM
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Originally Posted by predator carb guru
corection here

your right that most tachs use the ingition signal as the pickup for the tach, but tachs are designed to cut that speed in half to display crank speed

next time your out in you car do this

research and figure out the gear ratio of your car
drive down the road at a steady speed, say 40 mph
right down what gear your in and what the rpms are

multiply rpm's X gear ratio X final drive ratio X tire size ..... youll get the speed you were driving ... heres an online calculator that will do it for you :

proof that your tach is showing crank speed, because its the crank thats conectd to the transmission
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