Re: Rear gear ratio

Posted by Fred Puhn On 2011/4/4 10:50:27

Dear Tommycourt,
Some basic engineering information: torque breaks things, power does not (power overheats things). The Cadillac engine has about 60% more torque than the 288 Packard engine. If you drive the car using the available torque and use the stock transmission and rear end gears the stress on the rear axles will be about 60% higher than stock. They may or may not break immediately depending on how you drive, but the fatigue life will be shorter. The fatigue life is the number of load cycles it takes before small cracks form and eventually break the part.
You can bring the stress on the rear axles in high gear down to nearly the stock Packard level by using a 2.9 rear end ratio. You will need to change the entire rear axle housing probably since Packard never made such a gear ratio. That will also reduce the engine RPM and extend its life. Having less torque on the axles also means lower acceleration in high gear and less hill climbing ability. You can always downshift, but that increases the torque on the rear axles.
Before doing the engine swap you should consider all the costs and the many changes you need to make in the car to get a safe and reliable vehicle. The brakes and handling need to be considered too. In my opinion you would be better off financially buying a newer car rather than turning an old car into one.