Torque is the ability to overcome rotational resistance. High compression, large displacements, tight rings, blowers, and other factors all offer rotational resistance - and it takes torque to overcome this. Unfortunately, starters are rated in kilowatts. This is a measure of its torque and speed combined. The torque output is really unknown.
Starters, like engines, have different powerbands. Some have a maximum power point at a relatively high RPM with little torque. Whereas others produce more torque and yet lower RPM. In the performance environment, torque is the most important consideration, generally because a performance engine offers more rotational resistance than stock. As a result, kilowatt ratings can be confusing because two starters with the same kilowatt rating can have very different torque characteristics.
The engine will demand a certain amount of torque for cranking. When the torque demands cause a starter to exceed its maximum power point, the extra input energy is wasted as internal heat. Asking a starter to produce more torque than it is comfortable with results in low electrical to mechanical efficiency
and drastically increased internal heat. This is what causes premature starter failure. The key is to use a starter that has a power peak at a high torque point. Then, in the event that the cranking conditions offers high resistance, the starter will have the torque characteristics to handle it without overheating.
Several other factors effect starter performance dramatically. Voltage is very important. Cabling and quality
are important because under heavy load, voltage will be lost or "dropped" in undersized or hot cables, or hot switches. The internal resistance of the battery itself results in decreased voltage to the starter. Therefore, low internal resistance batteries like typical 1000CCA - or better yet - spiral cell AGM batteries such as Optima and others should be used. High voltage batteries like the new 16 Volt Powermaster battery is a perfect choice for any racing application.
When you purchase a Powermaster starter you will get a dyno sheet that shows you the exact performance of your starter. The sheet itself will explain how to interpret the data, but you can be assured that Powermaster starters are built to a consistent, statistically controlled standards, and that they are dynamically tested throughout their entire power range.