Upgrading the 410 Final Drive Ratio

[David C]

It would be interesting to know how Andrew's speedo reading compares with GPS.

For a standard 410 with 3.07 final drive if maximum maximum speed 130MPH coincides with red line at 5000 ( I stand to be corrected...) then 70MPH will be at 2700RPM.
A change to 2.88 final drive will give 70MPH at 2532RPM.
So a drop of about 170RPM. Very similar to that achieved with a locking torque converter.

Change from 3.07 to 2.88 is a reduction of about 0.94:1 whereas standard Laycock overdrive and most modern 5th gears will give a reduction of about 0.75:1 to 0.8:1.
The Mopar overdrive really overdoes it with a drop of 0.69:1.

Applying a 0.69:1 overdrive to Andrew's 2200 RPM gives 1520 RPM and not the 1800 reported. As far as I'm aware Mopar didn't offer a different overdrive ratio so I'm quite confused.