The torque converter (TC) is probably one the most misunderstood pieces of equipment in all of automotive. Hot rodders (even experienced ones) often brag about having a "3500 stall speed converter", without even knowing what that implies (as you will find out soon, a 3500 stall speed converter would generally be useless on any street car short of the most radical of Pro Streeters). Some even boast of having just a "stall speed converter", which displays a stunning ignorance, because ALL automatic transmission equipped vehicles have a "stall speed converter" - it'* the number that makes the difference. The whole idea behind different stall speeds is to allow the car to launch at or just below the point where the engine makes the most torque. That way, the engine doesn't have to build up to the peak RPM point - all of the power is right there, on tap. If you've ever been to the drag strip, you have probably noticed that the cars rev way up before the light turns green - this is because most racing engines don't make substantial power until they are spinning over 3000 RPM. If these cars were using the stock stall speed, the tires would break loose long before the engine reached it'* optimum RPM. A higher stall speed converter allows the engine to rev up to this optimum point without breaking the tires loose.

So what is stall speed? This is another widely misunderstood term. In the simplest of definitions, stall speed is the engine RPM level at which the torque converter "locks" and overcomes whatever resistance is present to turn the wheels. This resistance is the weight of the vehicle, combined with any other factors (i.e. if you have the brakes on). The old definition of stall speed used to be the engine RPM at which the brakes can no longer hold the wheels still at full throttle. This is not exactly accurate, due to the variations in brake holding power from vehicle to vehicle. In other words, in two cars that are exactly the same weight, horsepower, etc., the one with weaker brakes will display a lower stall speed, even if it really isn't, because the brakes will lose their grip at a lower RPM. The most accurate method for determining actual stall speed on your vehicle is to launch the vehicle at full throttle, and note the rpm at which the car actually takes off (this generally requires a partner watching the tach). This will be quite low on stock vehicles - around 1500-1800 RPM, slightly higher if the engine has been modified.

The next question probably goes something like, "If I already know the stall speed (i.e. what was printed on the box), why would that number change in my car?" The answer is that even though all converters have a rated stall speed (based on a fixed set of torque and weight figures), there are variables that affect this figure, mainly vehicle weight and engine torque. If you are really sharp, you may have already figured out why these two variables affect the stall speed. Weight affects the stall speed because it changes the amount of resistance that the converter has to overcome. A lighter car produces a lower stall speed because the amount of resistance (weight) has been decreased. By the same token, a more powerful engine also lowers stall speed because in the simplest terms, increasing engine power has essentially the same effect as decreasing vehicle weight.

Obviously it is extremely important to know what your vehicle'* weight and peak torque is before ordering a torque converter. One of the worst mistakes in all of hot rodding is to buy a converter with a stall speed that is too high. This usually results in a car that is not only slower than it used to be, but also gets horrendous fuel economy and eats transmissions. This is because the converter is slipping all of the time, absorbing power and passing it along as heat to the rest of the transmission. If Joe X. tells you that his TPI equipped 305 Camaro has a 3500 stall speed converter, and you're reasonably sure that he'* telling the truth, challenge him to a race and bet large amounts of money on it. Why? At 3500 RPM, TPI in stock trim is pretty much at the end of it'* torque curve, meaning that most of the engine'* usable torque is absorbed by the converter and passed along as heat. The same exact car with a stock converter would destroy Joe'* car off the line, because the stock converter is designed to take advantage of the TPI'* excellent low end torque output by using a stall speed of under 2000 RPM, right under the peak torque.

Probably the most important factor to consider when selecting a torque converter is the camshaft. The connection may not seem obvious, but the fact of the matter is that the camshaft basically dictates the RPM level at which the engine will produce it'* peak torque, which will in turn dictate the optimum stall speed. If your camshaft has a duration of 220-230 degrees (@ 0.050" lift) or more, you definitely want to think about a higher stall speed converter, probably about 1000 RPM over stock, because the engine will probably make peak torque at well over 2000 RPM. A general rule of thumb is that most stock small blocks (especially TPI equipped) are designed to make most of their torque at low RPM, while small blocks with high horsepower generally lack low RPM torque. Does this mean that you shouldn't bother with an aftermarket converter if you don't have a radical cam? No. Performance converters are usually designed to accelerate more aggressively than stock, so an aftermarket converter with the same stall speed rating as stock will often be more responsive than the stock unit. You just want to be very careful about the stall speed that you select.

Here are some general guidelines for selecting a converter:

According to B&M, the stall speed should be rated at about 500-750 RPM under your engine'* peak torque RPM. If you don't know this figure, be conservative in your estimate. You don't want to end up with a converter that has too high of a stall speed. Don't be too conservative, though - it is possible to get a converter with too low of a stall speed, which will have roughly the same effect as too high of a stall speed.

Know your camshaft specifications. If your cam has less than 220 degrees duration (@ 0.050" lift), which most street machines do, you make most of your torque down low in the RPM range, and you probably won't need more than a 2500 RPM stall speed, if even that much.

Have a good idea of your vehicle'* weight. Remember, lighter vehicles will lower the rated stall speed; heavier vehicles will have the opposite effect.

High stall converters generate a lot of extra heat. The installation of an external transmission cooler is mandatory with a higher than stock stall speed converter. Actually, you should have one in there anyway. Heat is the number one killer of transmissions - 85% of all trannies die because of inadequate cooling.

The best advice I can give anyone buying a converter is to talk to the manufacturer. They know torque converters better than anybody, and can help you to select exactly the right converter for your combination. This article was designed to give you some insight into what is needed to determine the right converter, and to make you familiar with the terms and what you need to know to speak intelligently with the experts.

What does "new technology" mean?

Torque converters have been around for over 50 years and converters continue to evolve at the pace automobiles have. PROTORQUE utilizes only the latest technology for both the core product and our modifications. Car manufacturers have spent a lot of time and money in developing vehicles that meet today'* CAFE standards. One of the ways they have done this is through driveline advances, and the torque converter is one of the key components in this development.Many of our competitors use torque converters that were designed in the 70'*; some even use converters that were developed in the 60'*.AtPROTORQUE, we use converters that have been developed in the 90'*; made to withstand the hi-tech, high horsepower of today. These torque converters are far superior in design because they have better torque multiplication rates and are more efficient. For example, the torque converter we use for our 4L60/700R4 was originally designed to go behind a 300hp late-model engine that is still in production today. The question you have to ask yourself is: What torque converter do I want to use for my 1998 Corvette, or my 1992 Camaro or my brand new Dodge truck, or my high-dollar street rod, or my hi-tech import? Certainly not a unit designed 30 years ago!

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What is stall speed and how do I determine what stall I have now?

Stall speed is a term used to describe the rpm at which the torque converter transfers the power from the engine to the transmission. There are different ways to test stall speed. "Foot brake stall" is when you press the brake pedal and then press the gas pedal. When the car doesn't go anymore or the tires start to spin that is "brake stall". (DO NOT TRY THIS! THIS MEASUREMENT IS MEANINGLESS AND POTENTIALLY DANGEROUS TO YOU AND THE TORQUE CONVERTER!) "Flash stall" is when you, from a dead stop, press the gas pedal to wide open throttle (wot). Watch your tach needle, you will see the needle jump to a certain rpm, that is "flash stall". A drag racing-style trans brake will give you closer to the true stall speed of a torque converter.
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What is torque multiplication?

Torque multiplication is a term used to describe the amount of torque the torque converter will multiply. A torque converter is basically a fluid coupling between your engine and transmission. There is no direct mechanical link until the torque converter is in lockup mode. The pump assembly of the torque converter is directly linked to the crankshaft of the engine, however the turbine assembly of the torque converter is not. It is connected to the transmission input shaft. When the oil is pumped to move the turbine it is actually pushing the turbine at a higher rate. Each torque converter pump and design pushes the fluid differently, therefore giving you different rates of turbine speed . All of this only means that different torque converters will give you different torque multiplication rates simply by design. Our goal is to design the best torque converter using the highest multiplication rates for your application.


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What does torque converter efficiency mean?

Once the torque converter does it'* job multiplying torque for take off, the function of the torque converter is to be a link (sometimes called a fluid coupling)from the engine to the transmission. Keeping in mind that the pump assembly and the turbine assembly spin at different speeds, every torque converter has a different rate of slippage between the two. The amount of slippage is what determines efficiency. This is why auto manufacturers created lockup torque converters. Rather than having a torque converter that is let'* say 92% efficient, they mechanically link the engine to the transmission, giving it a 1:1 ratio or creating 100% efficiency. This lowers the rpm of the engine, therefore increasing fuel efficiency.


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Why do I need a higher stall speed converter?

Theoretically, for maximum acceleration the stall speed of the torque converter should match the peak torque rpm of the engine. A good explanation for the way it works is this: when you go outside jogging you start to breathe in and out faster and harder. Well the same thing goes for a performance engine. The engine is breathing in and out harder and faster, at a higher rpm. If a high performance engine makes power at a higher rpm, then a higher stall speed torque converter is what you need to put more power to the ground quicker.


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Why is a torque converter the best performance upgrade money can buy?

Theoretically, for maximum acceleration the stall speed of the torque converter should match the peak torque rpm of the engine. A good explanation for the way it works is this: when you go outside jogging you start to breathe in and out faster and harder. Well the same thing goes for a performance engine. The engine is breathing in and out harder and faster, at a higher rpm. If a high performance engine makes power at a higher rpm, then a higher stall speed torque converter is what you need to put more power to the ground quicker.


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How do I determine the best converter for my vehicle?

This can sometimes be a difficult question to give a general answer to. In many cases performance and driveability are somewhat of a trade off. Generally with a higher stall speed you loose some of the driveability, and the driveability increases with a lower stall speed. Our goal is to manufacture a torque converter that will increase performance without sacrificing driveability. The most important thing to keep in mind, when selecting a torque converter, is that you want to match stall speed to the engine'* power band. Most cam manufacturers will give you a minimum and maximum rpm range. This minimum rpm really should determine what stall speed that you will need.


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Why use a "Custom Built Torque Converter"?

You have your heart and soul into your car. You have spent countless hours planning all the modifications. You have spent as much time making these modifications. You have picked the best of everything. Are you going to call a company that will sell you something off the shelf, because they have it stock, that only kind-of fits your application? I don't think so! We put as much care and workmanship into helping you decide what product you need as we do into developing the product you put in your car. And if that product is something we haven't developed yet, you can rest assure that we will take the time to develop a specific torque converter for your application!


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How do I make a final decision on a torque converter?

Use a company that offers you as much information as possible. Use a company that offers you a warranty. Use a company that utilizes all the technology available today. Use a company that will help you make a decision on what product that you need for your vehicle. And most of all, use a company that you know is building the best torque converter on the market today! Use PROTORQUE.


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Are there any other upgrades that I should consider when installing a new torque converter?

You might want to consider a performance tire upgrade such as a "drag radial" tire. Traction will be your biggest problem. Take for example the testing we did with our 1998 Corvette. After the torque converter swap, we couldn't believe the amount of tire spin. By putting power to the wheels, at a higher rpm, you begin to realize that a suspension upgrade might be a necessary upgrade as well. The only other recommendation is, depending on the application, some performance torque converters create more heat and long term heat kills transmission life. A light bulb that burns twice as bright burns half as long. This is why we carry a full line of "stacked plate" transmission coolers. Tests have shown that these coolers can increase your cooling capacity by 100%.


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Is installation of a performance torque converter difficult?

Again this can be a difficult question to give a generic answer to. In most rear-wheel-drive cars installation is relatively simple for someone who has some mechanical background and the proper tools. In cases such as the new C5 Corvette or a 4WD Eclipse Spyder installation is better left for a professional. In depth installation tips follow and can be downloaded from this web site.