Sorry, I am not a math guru, explain K factor equasion?

Labeling a converter as having a specific stall without reference to the motor it is behind is misleading and naive. That stock converter, which stalls at ~1,500rpm behind a stock motor, might stall at 3,000rpm or more behind a blown big block, if it didn’t blow up first! To elaborate a bit: stall speed is not just a function of the converter. It is also a function of engine torque. This can be relatively easily described by defining the “K” factor. K is simply the constant in the equation K = rpm/sqrt{torque}. The equation describes the observed behavior of the converter behind a specific engine. What this allows us to do is determine what the stall speed of a given converter will be if we put it behind a different engine.

For example, if a motor has 400 ft-lbs. of torque and stalls a particular converter at 3,000rpm, K = 3,000/sqrt{400} = 150. Since we know K = 150, we can predict the new stall speed if torque is increased to say 500 ft-lbs by rearranging the equation to rpm = K*sqrt{torque}. In this case, the new stall would be rpm = 150*sqrt{500} = 3350. This formula isn’t perfect. It won’t work if the engines have wildly different torque curve, for example. And it won’t tell if a particular converter will hold together under markedly increased torque. But it gives a decent ballpark estimate and serves to illustrate a basic aspect of torque converter function. For most street and street/strip, you probably want a stall in the 2,500-3,500rpm range. But do not buy an off the shelf converter thinking it will give you the advertised stall unless it has been proven to do so on an identical setup. Speak to the manufacturer first to be sure you are getting what you need for your particular combo.