25/09/2023
Stall Speed; It’s not magic, its math….
Lets talk “stall speed” the most common yet most misunderstood term used when talking about a torque converter. The main problem we come across is most people dont understand what a torque converter is or more so how it even works. I would have to do a very lengthy write up here to truly breakdown what the entire assembly actually does and how it does it. For now we will just go over key points to keep it simple. In the end, Its not magic, its math.
A torque converter has 3 main stages of operations, stall, acceleration and coupling. Then you have the main three when it comes to the components within the torque converter, the pump, the stator and the turbine.
Lets talk about the stator and its effect on the stall that is so commonly talked about. Yes I know the stall can be manipulated by changes to the pump and turbine but this also effects to the other two stages of operation. Remember “stall” is just one of 3 important operations, you can’t change one without effecting the others. We can and will discuss these other operations and components all in detail at a later date. Today is for the stator.
The stator is located in the very center of the torque converter. The stators main role of operation is to redirect the fluid returning from the turbine before it enters the pump . This will increase or decrease the overall efficiency of the torque converter with all variables staying the same ( turbine and pump). To give you a very brief description of what role the stator plays; IF you were to remove the stator all together there would be no “magic” of multiplying torque, you would just have a fluid coupler device. So once again the stator design can increase or decrease the efficiency of how that fluid transfers from the turbine to the pump, this once again is where the “magic” of the torque converter happens but dont forget all three of the main components will effect the main three operations of the overall unit.
In the end a torque converter is a load-sensitive device. The torque converter sees input load aka; engine output torque, as well output load created by the vehicles gear ratios, vehicle weight, tire height, among other load applying variables. Here it is again, its all math, not magic. To break this down into very simple layman’s terms, the same exact pump/turbine/stator combination will have very different actions on all three operations based on the overall torque applied to the torque converter on either end.
Here is an example; let's take our 8HP torque converter with an advertised stall speed rating of 3,000 to 3200 RPM in an 8HP50 equipped application. This converter in a very common combination within a BMW with a 3.0 engine with the typical bolt-on mods will yield a stall speed within the advertised stall range. These combinations are known for high torque outputs at a very low rpm range due to the engine output characteristics.
Now lets take that same BMW with a 3.0 engine and put a much larger cam and turbo combination and supporting mods which shifts the torque curve to the right in the RPM range. This will result in less stall speed. In this specific example, we could realistically expect to see anywhere from 400 - 600 less flash RPM as compared to how the converter would react behind the larger amount of torque produced by the bolt on car.
Now lets take this BMW with a 3.0 engine just as above with the larger cam and turbo combination etc and add a launch control or anti-lag strategy to the mix where the engines output torque can be vastly increased at lower RPM and this same exact converter configuration will stall at over 1000rpm higher then it did in our first example.
I know this is alot to take in and there is a whole lot to be discussed but this is why torque converters are not a one size fits all deal.
This is why it is absolutely crucial to consider all possible parameters of your combination when contacting us for a torque converter for your project.
