For straight line guys, spending hundreds of dollars on something that doesn't give you any extra horsepower doesn't exactly seem like a good deal. Even a federal bean counter could figure that one out. Unless that money buys extra hook off the line, your suspicions of lameness are usually true. However, the one exception to the rule is a high-stall torque converter. Sticking one of these fluid-filled donuts between the engine and trans can often shave a half-second off your quarter-mile e.t.'s. It's all about maximizing power off the line, and nothing accomplishes this better than an optimized torque converter. By allowing a motor to freely rev to the fat part of its powerband almost instantaneously, instead of lugging along at low rpm where torque is at a premium, the result is blistering 60-foot times and phenomenal gains in acceleration. To put it succinctly, all automatic-equipped street machines and drag cars need an aftermarket torque converter.
In essence, a torque converter is nothing more than a fluid coupling that transfers power from the engine to the transmission. Unlike the clutch in a manual transmission, the input side (impeller) of the converter isn't physically connected to the output side (turbine). Instead, converters transfer power from one side to the other by swirling transmission fluid around inside their housings. It's this peculiar dynamic that offers endless tuning possibilities when the task at hand is torque multiplication and powerband optimization. Consequently, torque converter design is a very complex science where simple changes to the length, size, and shape of its internal blades and fins dramatically alter its performance characteristics. Likewise, there are a multitude of ways to build a converter to achieve the same specific performance goal. To get a handle on it all, we contacted two of the sharpest minds in the business, Stanley Poff of TCI and Joe Rivera of Pro Torque. Here's what they had to say.
Stall It
Stanley Poff: "When extracting more horsepower from an engine with components such as a performance intake manifold, fuel delivery system, camshaft, and valvetrain, it's imperative to upgrade from a factory converter to a performance aftermarket unit. In most cases, horsepower has been increased and a more durable torque converter is needed. Likewise, changing the torque converter to a higher stall speed increases torque multiplication and allows the engine to reach its powerband quicker. Raising the powerband of the engine requires flashing the converter's stall speed closer to the peak torque of the engine, and locking it as soon afterwards as possible. For example, if you have an engine that is making peak torque around 2,500 rpm and you use a tight stock converter which averages around 1,500-1,700 rpm of stall, there will be a lag time where the engine will simply not perform as well as it could until it reaches 2,500 rpm. By installing a torque converter that flash stalls to 2,500 rpm, the engine is allowed to reach its optimum hp range quicker and will therefore perform much better."