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New RPM Calculation...and speedo gear
To give you a quick calculation of the change in RPM you will see:
3.55/3.08 = 1.15…….so for a given speed, your RPM will be 1.15 times what it is now.
3.73/3.08 = 1.21…….so for a given speed, your RPM will be 1.21 times what it is now.
For example, if your engine is currently turning 1500 RPM at 60 MPH, if you change to a 3.55, you will be turning about 1729 RPM at 60 MPH after the change. If you change to a 3.73, you will be turning about 1817 RPM at 60 MPH after the change. Using the above calculations, try running in fourth gear at what the calculated RPM is, based on your current cruising speed RPM in fifth, to see if you like the sound or not.
It is also worth noting that if you do change the rear end ratio, you will also need to change the speedometer gear, or your indicated speed will be off by the above multipliers as well (ie., you will be going slower than indicated by 15% or 21% respectively). The speedometer is measuring the speed of the output shaft of the transmission and not the axle or wheel speed.
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If a man does not keep pace with his companions, perhaps it is because he hears a different rumble. Let him step to the sidepipes which he hears, however measured or far away. - H.D. Thoreau...if he had owned a Cobra
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