Torque Converter Stall Speed

Oct 12, 2011

With all the different stall speeds available, many customers in our market will ask which stall speed is “the best.” In short, there is no better stall speed; it’s about matching your needs to the right unit.

The other question we often get is what does that stall speed number even mean? Specifically to our market, that number doesn’t mean a whole lot. ZZP and the other vendors in our market label converters however we want. ZZP based our labels on what people had come to expect the numbers to mean. In other words, there is no technical explanation for the labels on our converters. Because there is not technical label, you may get a few very strange responses from individuals not familiar with our market. “OMG, you can’t run a stall that high!” or “That’s not enough converters (referring to the stall speed not being high enough).  Both of these responses are common responses from unfamiliar mechanics. They simply aren’t familiar with our rating system.

The technical explanation for stall speed is the amount of difference between the engine speed and the transmission speed. The problem is though, the stall speed changes based on the weight of the vehicle, speed of the transmission and most importantly, horsepower of the engine. This is why individuals must be familiar with our rating system to understand what the “best” stall speed is for their engine.

Higher stall converters allow better launches and lower end grunt because the engine can get higher into the power band while the transmission is still or at a lower speed. The sacrifice is in top end horsepower, gas mileage and heat. Below is a dyno of a maxed out M90 setup with and without the converter locked. It’s a ZZP 3500 stall converter. As you can see there’s a lot of low end power gained by letting the converter slip but there is also a large penalty up top. On our 2500 stall converter’s two lines wouldn’t be separated so far. We normally see only about 10HP lost up top. Because the 3800 with an M90 makes so much torque, we generally recommend our 2500 stall converter because more power at launch is not going to help as much as more top end power would help.