3.91s in my 340 now!

Wvbuzzmaster said

Rude72,
My Duster should be turning around 3200 RPM on flat ground at 60 with the 27” tall tire. Non lock up converter adds a couple hundred RPM from if it were a manual. But note I am usually turning over 3500 RPM on highway which is 70 MPH, which I find quite acceptable.

Speedometer is calibrated based off of axle gear and tire diameter, plus this fancy chart from Brewer. Then you add the correct number/color speedo gear in the tail shaft housing on your transmission, pretty simple.

Your next question of what color my 340 is might or might not be correct for year of car, but my non original 1969 340 is orange in my 1972 Duster.

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Thank you for all the information! Your numbers sound pretty similar to mine... no surprise there, though. A lot of people complain about the high revving rpm at highway speeds for 3.91 gears. It really doesn't bother me (I have 245/60/14 tires, which I believe are 26" tall). I was just a little concerned about the stress on the motor and other integral parts. And of course, the motor running hot.

So I'm guessing the rear-end/differential needs to be exposed to calibrate the speedo. That's definitely NOT me. I am a complete novice when it comes to working on cars... but I am slowly getting acquainted with it.

Beautiful Duster! Love the color! Thank you so much for sharing!