![]() ![]() Labeling a converter as having a specific stall without reference to the motor it is behind is misleading and naive. Again, close cooperation with the converter manufacturer is the best approach. Some people advocate a bit above, others a bit below peak torque rpm. For best drag strip results, we like to see a converter that stalls close to peak torque. To get a converter that stalls at the right speed for your application, you need to speak to the converter manufacturer. Of course, what is tolerable to one person may not be to another and vice versa. Stock converters typically stall in the 1,500-2,000rpm range. For example, a given combo may need a 4,500-5,000rpm stall for the best 1/4 mile times but be annoying on the street due to excessive “slippage” but a converter which stalls at 3,000-3,500 will allow tolerable street driving without too much effect on the 1/4 mile performance. The improvement all comes in the first part of the run, and interestingly, trap speeds may decrease due to the inefficiency of the higher stall converter at high speeds.įor a street/strip car, converter stall is a compromise. To illustrate how this works, there can be up to 0.5sec or more improvement in 1/4 miles times by switching to a high stall converter. When you stab the gas, there is a delay while the engine revs before the car starts to accelerate. Also, a high stall can be annoying to drive on the street because it degrades throttle response. On a street car, the penalty in gas mileage and heat generated by a high stall converter favors a lower stall. Allowing the engine to get into the power band quickly more than compensates for the disadvantage of lower efficiency. A converter optimized for drag racing will have a stall speed much higher than a street converter. So why would you want a high stall converter? To allow the engine to get into the meat of the power band quicker. In general, the higher the stall, the less efficient the converter is at high speed. The rpm achieved (stall speed) will be a function of the engine torque and the converter design. Stall refers to the maximum speed a the motor can achieve against the converter when the turbine is locked and prevented from rotating. Obviously, you need a good transmission cooler if you use a high stall converter. This generates enormous heat and pressure. When a trans-brake is used, for example, the converter has to absorb the full power of the engine with the turbine locked. All of the parts including the case need to be strengthened to absorb the high loads. A lockup TC has clutches that link the impeller and turbine, thus allowing near 100% efficiency at high speeds.Ī race quality converter can be quite expensive. A non-lockup TC absorbs ~2-7% of total engine power due to the “slippage” that exists between the impeller and turbine. Once the impeller and turbine speeds approach each other, torque multiplication decreases to essentially zero. As speed increases, the torque multiplication decreases. Maximum torque multiplication occurs at rest, as the vehicle just starts moving. The stator (in the middle, between the impeller and the turbine) plays a role in directing the fluid so that it efficiently interacts with the impeller and the turbine.Ī characteristic of a TC is that it multiples torque, by a factor as much as 2-2.5 times or even more, depending on the design. The fluid flows from the turbine to the stator (in the middle of the converter), which freely rotates in one direction due to a one way clutch. The force of the fluid flow causes the turbine to rotate. The fluid flow is directed first against the turbine, which is coupled to the input shaft of the transmission. When the crank turns the case and impeller rotates and generates fluid flow. The crankshaft is connected to the case through the flexplate and the impeller is mounted to the case. They reside inside the case, which is filled with automatic transmission fluid. Very simplified, a torque converter (TC) has three major internal components. Electronic Fuel Injection – Aftermarket ECU’s. ![]()
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