Those who insist on rowing their own gears just might be insecure in their manhood. If you're into sacrificing big wads of e.t. in order to feel extra tough, you probably have issues-the main one being chronic dragstrip defeats. Real racers run automatics, but unfortunately, the road to straight-line heroism is often littered with expensive driveline shrapnel. For some expert advice on how to extract maximum performance and longevity from trannys and torque converters, we had a chat with Stan Poff of TCI Automotive. Since transmissions fail as often as celebrities enter rehab, and few components effect e.t. as profoundly as a properly matched torque converter, it's advice worth listening to.
Most hot rodders know that a tranny cooler is something they should install, but many just haven't made the time to do so. Unfortunately, such a casual attitude may not be the right approach. "In any place other than Antarctica, you should install a transmission fluid cooler," opines Stan. "Anytime you separate the cooling of the transmission fluid from the radiator, where the temperature can run over 210 degrees, you will promote longer transmission life. Instead of the transmission fluid only being cooled to the temperature of the radiator coolant, it will now run about 20-30 degrees cooler than the engine by using a separate transmission cooler."
While stall speed represents where in an engine's powerband a converter will flash, it doesn't indicate how much the converter will multiply torque. A converter multiplies engine torque at a 2- to 3:1 ratio (known as the multiplication ratio), so stall speed isn't the only thing you should pay attention to. "Multiplication ratios can vary from one converter to the next, depending on a converter's internal component makeup," says Stan. "For example, we can build three torque converters that have the same stall speed, but different multiplication ratios simply because of the different combination of stators, fins, and clearances used in each unit."
Stall speed is a measurement of how high a converter will flash in a specific application due to engine torque and load. The "flash" point, simply put, is the rpm at which a car moves from a dead stop under full load. The torque converter's diameter, fin angles, internal parts clearances, and stator design are some factors that determine stall speed. Matching stall speed to a given application is critical for optimum performance, but the advertised stall speed of a torque converter is just a ballpark figure. "Stall speed varies depending on the load placed upon the converter from the engine and the vehicle weight," explains Stan. "If you have two vehicles with identical motors and rear gear ratios, and the only difference between them is vehicle weight, the same converter will stall more in the heavier car, because it sees more load. Likewise, if you have two identical vehicles with the exception that one produces an extra 100 lb-ft of torque, the vehicle with more torque will flash its converter 200 or 300 rpm higher, so this should all be taken into consideration when choosing a converter."