TH 400 vs 350 vs 200 metric

[Alan Roehrich]

A low torque and HP car that turns a fair amount of RPM will see more gain from light weight transmission pieces than a high torque lower RPM car.

A car with less torque and HP that is turning a fair amount of RPM will often see fair amount of RPM drop.

The input drum spins at a percentage of the engine RPM, more specifically, the input drum is spinning at whatever the percentage of slip is in the converter at any given time.

On a normal 350 or 400, the 1-2 shift stops the direct drum, which has been spinning. Engine RPM drops, and so does the input drum RPM, so you accelerate the input drum again in 2nd gear, while holding the direct drum still. On the 2-3 shift, the direct drum instantly accelerates to the speed of the input drum as soon as the direct clutches engage fully. So 3rd gear shift you accelerate the direct and the input drum back up to whatever percentage of engine RPM the slip in the converter allows for.

Now, the further the RPM drop between gears, the more you have to accelerate those pieces. This soaks up some amount of torque, so, the less torque you have, the more there is to be gained with lightweight stuff.

Some of the higher HP cars have reported little or no gains from switching to a "trick" transmission such as a Pro Trans or a Kilgore, from a light 350, while others have reported 3-6 hundredths. The same applies to switching from a light 350 to a 200.

A fully lightened 400 can approach the same weight and efficiency as a 350, at a higher cost, with a greater margin of reliability, but at an increased cost, due to the cost of the gear set and the aluminum reaction carrier. The ET difference to a low RPM high torque car may not be enough to measure.

A car with a lot of torque may not even want or like a low gear lower than about 2.5:1, it may even slow it down, because of the extra time spent slipping the converter.