High Performance Torque Converters explained....

The Basics Of Stall Speeds
A torque converter’s job is to take the horsepower an engine produces and multiply that to make the car accelerate. The torque converter is a hydraulic coupling which takes the engine’s mechanical force and converts it into hydraulic pressure. Its impeller turns at engine speed; the more torque the engine makes, the higher in the RPM range the converter will “stall”, or lock up. The stall speed (remember that!) is the level where the engine’s force can’t overcome the hydraulic pressure, and varies for a number of reasons. The action of the converter’s stall is what helps the car accelerate at a peak level once the driver applies the power to the driveline.
The main factors that go into calculating the stall speed for any car include the weight of the car, the circumference of the rear tires, the gear ratio, and of course, the engine’s performance level. With the engine, even the camshaft must be taken into consideration to make sure the stall speed is matched up when the engine comes alive in the power-band. Making the correct choice in stall speed is important because it allows the car to launch harder and have improved 60-foot times — both critical factors in laying down fast and consistent elapsed times
The hard parts of the torque converter that really affect the stall speed are the overall size of the converter, the pump blade angle, and the stator. By making changes to each of these parts, a torque converter manufacturer can dial-in where the converter will begin to stall the engine.
Torque converters come in a range of sizes, and that size will impact how the converter will behave with an engine. Depending on the engine combination you’re using, choosing a converter that is sized to what its output capability is will vary.

The Stall Speed Range
There can be some confusion that the stall speed of a torque converter is an absolute thing. The reality is that a torque converter has a range of speed that the stall can engage in, and that will change based on the previously mentioned factors.
Stall speed is a relative term. It only reacts to a situation; it does not dictate anything. The same converter will flash differently when put behind different powerplants or in different cars. It will even change with the weather, so there can be no exact stall speed.
For a race-only application, the basic rule is to get the converter to flash just above peak torque. For a car that is setup for street/strip use, you will need to be a little more conservative, but you still need to ensure it gets past what we call ‘the stumble zone.’ The object is to get the engine into an area of the power-band where it’s happy and can accelerate easily without stumbling.”
Heat is one of the biggest issues that plague a converter. Too much stall and people tend to short shift, leaving them in high gear at 20 mph and making the converter do all the work; this is a bad scenario. If you choose to run a loose converter on the street, you must wind up each gear and let the converter couple before shifting. This can make a world of difference on the temperature gauge
It’s also possible to go too tight with a converter in your street/strip car, and that will cause its own set of issues. The converter and transmission might not be seeing nuclear levels of heat and the drivability might be better, but the performance at the track will suffer. The car will seem very lazy when you launch, and your 60-foot times will be poor, causing your elapsed times to rise.
Stall speed: it’s a number that’s attached to every torque converter, and is one of the key elements in making a vehicle perform at its highest level. There are many factors that go into choosing the correct stall speed for your car, and each must be examined in order for the torque converter to do its job properly. Let our experience guide this selection as tied to the modifications you have!

What converter is best for me?
The more torque your engine makes, the more holding capacity you need from your torque converter. You also have to be aware of that capacity, because you can’t have too much or it will hinder performance at the track. If you have too little holding capacity, you will start to blow through your converter and experience slippage. The RPM range of the torque and horsepower curves are most important in configuring a converter correctly for a given engine combination.
If you’re planning on bringing a power-adder into the mix with your car, that will absolutely require a change in your torque converter’s stall speed. Changing where the car has power being brought in and the amount will cause the converter to hit its stall point at a different place overall.
A converter reacts to two things to multiple torque: force applied from the torque of the engine, and resistance, which is the car. When the vehicle has a power-adder, that will need to be factored into the choice of torque converters. The reason for that is because no matter what power-adder you opt to use, it will change not only how much power the engine makes, but where it makes it. Where that power comes in will drastically change what the converter does, so a nitrous converter won’t be effective in a boosted application.
As mentioned earlier, besides the engine’s ability to produce power, the weight, gear ratio, and tire height all play a role in what the converter’s stall speed needs to be. The heavier a car is, the more load it will put on the torque converter when power is applied, causing it to flash at a higher speed. Gearing plays a part because as you add more gear, it will cause the load on the converter to become lower, while taking away the gear will make the load grow. Tire height falls into the same function zone as the gearing of the car: as you increase the height of the rear tire, you will increase the load on the torque converter and change where the torque converter will flash.
Power adders such as centrifugal superchargers and turbocharger systems; tend to benefit much more with a higher stall converter. This is because power is typically increased linear as rpm pickups vs a positive displacement supercharger or nitrous that can make a lot of power at lower rpms. The converter basically allows you to get “into” the power quicker which leads to a quicker accelerating car!
Keeping a Converter Healthy!
The critical factor to remember is that heat kills. You want to make sure that you keep as much heat out of the transmission and converter as possible.
You want to be sure to run a suitable transmission fluid and have an adequate transmission cooler. The newer transmissions like to run hotter than the older ones, and that’s okay, because their fluids are capable of withstanding more heat. Older transmissions are happy in the 160- to 180-degree range. The newer transmission you can run around 180- to 200-degrees. Anything over 200-degrees is a cause for concern. Street cars have a higher tendency to build heat then a race car does so cooler type and installation is critical to the life of the converter and transmission!





