Re: top speed for a 21 super clipper with 356 cu. in

Posted by Tim Cole On 2020/3/2 9:02:35

It depends on the condition of the engine. An engine in worn condition may not have the horsepower to pull the overdrive at higher speeds.

It works like this: For the Packard motor at least 45% of the power output is used just to make the crankshaft go around. The horsepower required for a given speed is fixed. So if you reduce the engine speed 20% you reduce the amount of fuel required to turn the motor - hence the term Econo-Drive. The fuel required to maintain the speed is still the same.

As well, if the overdrive puts the motor rpm below the level required for a given speed the car will not go any faster regardless. This actually is a fairly common result. Take some modern cars with paddle shifters. Some of them go faster in the next lower gear.