Maximum-Strength Performance Automatic Transmissions - CHP How It Works

Top Industry Pros Explain The Art Of Building Maximum-Strength Performance Automatics

Stephen Kim Aug 24, 2010 0 Comment(s)
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"The planetary gearsets we use consist of a sun gear, a ring gear, and three or more planet gears, all remaining in constant mesh. The planet gears are connected to each other through a common carrier, which allows the gears to spin on shafts called pinions attached to the carrier itself. One example of a way that this system can be used is by connecting the ring gear to the input shaft coming from the engine, connecting the planet carrier to the output shaft, and locking the sun gear so that it can't move. In this scenario, when we turn the ring gear, the planets will 'walk' along the sun gear, causing the planet carrier to turn the output shaft in the same direction as the input shaft, but at a slower speed to achieve gear reduction.

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"If we unlock the sun gear and lock any two elements together, this will cause all three elements to turn at the same speed so that the output shaft will turn at the same rate of speed as the input shaft. This is like a car that's in high gear. Another way that we can use a planetary gearset is by locking the planet carrier from moving, then applying power to the ring gear. This will cause the sun gear to turn in the opposite direction, resulting in Reverse. The clutch pack is used, in this instance, to lock the planet carrier with the sun gear, forcing both to turn at the same speed. If both the clutch pack and the band were released, the system would be in neutral. Turning the input shaft would turn the planet gears against the sun gear, but since nothing is holding the sun gear, it will just spin free and have no effect on the output shaft. To place the unit in First gear, the band is applied to hold the sun gear from moving. To shift from First to High gear, the band is released and the clutch is applied, causing the output shaft to turn at the same speed as the input shaft."

Stall Speed
Zack Farah: "When it comes to torque converter stall speed, many people miss the mark because proper stall speed is dependent on a wide variety of factors. Based on our experience, the stall speed should generally be set at 300 rpm above the point where the cam lets the engine begin producing its torque curve. This is a good rule of thumb for street performance and driveability. For dragstrip-only use, many more factors must be considered such as body type, class rules, vehicle race weight, tire width and diameter, rear gear ratio, cubic inch displacement, stroke length, compression ratio, carb and manifold type, and all cam specs."

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Stanley Poff: "Stall speed selection depends on a wide variety of factors. First and foremost, you must determine if the car is a cruiser, a street/strip machine, or a race car. Once that's established, the weight of the car, ring-and-pinion ratio, engine displacement, and cam lift and duration all come into play. With this information, TCI technicians are trying to dyno the engine in their minds. The goal is to get enough stall to flash near peak torque yet not be too loose and allow the engine to run at high rpm, which will create excessive heat."

Transbrakes
Zack Farah: "Racers know that transbrakes help cars launch very hard, but they also help the chassis work more effectively compared to just foot-braking a car at the line. Transbrakes, when engaged, apply two different reaction clutches at the same time, which puts the trans in a bind. This way, the engine is held back and able to be brought up into its powerband without twisting the chassis. The result is a straighter, more controlled launch when the transbrake is released. Additional stress on the trans is irrelevant, as the cleaner launch is the objective. Transbrake packages are available from several sources, and there are several different engineering methods used to achieve the same result. Installing a transbrake requires many internal modifications, much more than a simple shift kit."

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