FREQUENTLY ASKED QUESTIONS
What is a torque converter? What is a lockup torque converter? What is a performance converter? How do I determine the best converter for my vehicle? How does the torque converter affect the performance of your engine package? How does the right torque converter prolong the life of the transmission? How does the torque converter work? What is the stator? Why do diesel powered vehicles require lower stall speeds than gasoline powered vehicles? What do you want from your torque converter? Why should you order your torque converter from Midwest Converters? What is the Mystery of Stall? Can you explain incorrect torque converter selection problems? What is the most common installation error? What do I need to know when calling the tech line for assistance? Explain lock up vs. non-lock up transmission – which is right for my street driven car? Electric vs. non-electric transmissions – which is better for me? Do I need a cooler for my transmission? The Big Stall – how do I find my torque converter stall speed? Why can’t I run an 8-inch torque converter in my street car? My transmission comes with an assortment of rings that allow me to adjust by speedometer – which one is right for me? When should I use a clutchless automatic transmission? Is an additional oil cooler required with high performance converters? What is Midwest Converters warranty policy?
WHAT IS A TORQUE CONVERTER?
A device for changing the torque-speed ratio or mechanical advantage between an input shaft and an output shaft. A pair of gears is a mechanical torque converter. A hydraulic torque converter is an automatically and continuously variable torque converter, in contrast to a gear shift, whose torque ratio is changed in steps by an external control.
A mechanical torque converter transmits power with only incidental losses; thus, the power, which is the product of torque T and rotational speed N, at input I is substantially equal to the power at output O of a mechanical torque converter, or T1N1 = kT0N0, where k is the efficiency of the gear train. This equal-power characteristic is in contrast to that of a fluid coupling in which input and output torques are equal during steady-state operations.
In a hydraulic torque converter, efficiency depends intimately on the angles at which the fluid enters and leaves the blades of the several parts. Because these angles change appreciably over the operating range, k varies, being by definition zero when the output is stalled, although output torque at stall may be three times engine torque for a single-stage converter and five times engine torque for a three-stage converter. Depending on its input absorption characteristics, the hydraulic torque converter tends to pull down the engine speed toward the speed at which the engine develops maximum torque when the load pulls down the converter output speed toward stall.
McGraw-Hill Encyclopedia of Science and Technology, 5th edition, published by The McGraw-Hill Companies, Inc.
It transfers engine torque to the transmission allowing the vehicle to come to a complete stop without stalling.
It multiplies the engine torque to the transmission resulting in greater vehicle performance.
It provides a direct-drive, or mechanical link from the engine to the transmission, which is accomplished by using a torque-converter clutch.
WHAT IS A LOCKUP TORQUE CONVERTER?
Pumping losses within the torque converter reduce efficiency and generate waste heat. In modern automotive applications, this problem is commonly avoided by use of a lock-up clutch that physically links the pump and turbine, effectively changing the converter into a purely mechanical coupling. The result is no slippage, and virtually no power loss.
The first automotive application of the lock-up principle was Packard’s Ultramatic transmission, introduced in 1949, which locked up the converter at cruising speeds, unlocking when the throttle was floored for quick acceleration or as the vehicle slowed down. This feature was also present in some Borg-Warner transmissions produced during the 1950s. It fell out of favor in subsequent years due to its extra complexity and cost. In the late 1970s lock-up clutches started to reappear in response to demands for improved fuel economy, and are now nearly universal in automotive applications. Wikipedia
WHAT IS A PERFORMANCE CONVERTER?
A performance torque converter is designed to match the performance characteristics of your vehicle or to accomplish a specific level of desired performance. They are manufactured differently than regular stock torque converters:
Components are strengthened to accommodate the additional power.
Internal characteristics of the torque converter are altered in order to transfer the additional power.
Stall speed is adjusted to more closely match the power curve of your specific performance requirements.
HOW DO I DETERMINE THE BEST CONVERTER FOR MY VEHICLE?
There is no general answer to this question unless the application is for stock use. The answer is simple then; a stock converter for a stock application. Because each performance converter is built for your specific needs it is best to supply the online data relative to your needs or call us toll free and speak to one of our experts to determine your perfect torque converter. 815-229-9808.
HOW DOES THE TORQUE CONVERTER AFFECT THE PERFORMANCE OF YOUR ENGINE PACKAGE?
Whatever level of power you have created with your engine, it is the job of the torque converter transfer that power. You will waste that power if you are use an inferior OE torque converters with your performance package. A performance torque converter is designed to work in concert with the engine will maximize its power to the wheels.
HOW DOES THE RIGHT TORQUE CONVERTER PROLONG THE LIFE OF THE TRANSMISSION?
The right torque converter reduces slippage thus producing less heat for longer transmission life. The proper cooling system is also essential to prolonging the life of the transmission.
HOW DOES THE TORQUE CONVERTER WORK?
The torque converter is a fluid pump that shares fluid with the transmission. That fluid is pumped outward toward the outside of the torque converter. An impeller, which is similar to a small fan, is inside is the torque converter. It uses centrifugal force to pump the transmission fluid. The impeller faces the turbine of the engine. The faster the turbine spins, the faster the impeller spins and, subsequently, more torque is transferred from the engine to the transmission.
WHAT IS THE STATOR?
The stator assembly is in the very center of the torque converter and redirects the flow of fluid returning from the center of the turbine in the same direction that the engine is turning the converter pump.
WHY DO DIESEL POWERED VEHICLE REQUIRE LOWER STALL SPEEDS THAT GASOLINE POWERED VEHICLES?
Performance gasoline engines produce power at a higher rpm and need a higher stall speed torque converters to put more power to the wheels quicker. Performance diesel engines produce power at a lower rpm and need a lower stall speed torque converter to put more power to the wheels quicker. Typically, when achieving maximum acceleration, stall speeds will match the peak torque rpm of the engine. By lowering the factory stall speed from 2,000-2,500rpm level to the 1,600-1,900rpm range, where most diesel engines produce maximum torque, significant gains can be made in acceleration, throttle response, fuel efficiency and towing.
WHAT DO YOU WANT FROM YOUR TORQUE CONVERTER?
We will customize your torque converter, whenever possible, relative to your desires. Please take the time to supply us with your vehicle specific information and our experts will provide you with the right converter.
WHY SHOULD YOU ORDER YOUR TORQUE CONVERTER FROM MIDWEST CONVERTERS?
The answer is simple. With over 40 years of experience in the torque converter and transmission industry and our famous Limited Lifetime Warranty we can provide you with the customized service your individual desires require.
WHAT IS THE MYSTERY OF STALL?
The most confusing issue between the High Performance torque converter builder and the customer is the word STALL. Torque converter stall speed is the RPM a given torque converter combination allows the engine to attain with a given engine torque input.
Brake Stall is attained when the transmission is put in gear and the brakes are held with the brake pedal and the accelerator is slowly pushed to the floor. The RPM the engine reaches the moment the rear wheels of the vehicle start to spin is known as Brake Stall. Because the rear brakes cannot handle the torque multiplication of the torque converter this stall speed figure will be very low, approximately 800 – 1000 RPM under True Stall.
Flash Stall is attained when the vehicle is driven at a very slow speed then accelerated hard by depressing, the throttle to the floor while looking at the tachometer and noting what RPM the engine has reached. If the wheels spin the reading will not be accurate, thus making this method not as accurate as others. Installing a manual valve body in the transmission makes this method very accurate by allowing you to shift the transmission in to high gear and then accelerate from a standing start with very little chance of tire spin.
True Stall is the most accurate of the stall readings and the method you will want to use. True Stall is the holding RPM of the torque converter with the engine at wide open throttle and the transmission locked so the driveshaft cannot rotate. Remember that Stall speed varies depending how much torque is applied to a given combination in the torque converter. For example if you had a torque converter behind an engine that developed 400 HP and True Stall tested it and the engine RPM reached 4500 RPM you would identify this as a 4500 RPM stall converter. Likewise, if we took the same converter and put it behind an engine that developed 800 HP and we then True Stall tested it and the engine RPM reached 6000 RPM we would call this a 6000 RPM stall converter.
Many variables will determine the correct Stall Speed for your desires. Please provide us with your specific vehicle information and one of our experts will determine the perfect torque converter for you.
Can you explain incorrect torque converter selection problems?
As owners add engine power, they often install a looser torque converter (higher stall speed), overshooting the power range. A tighter converter will provide more bottom end power. As a guideline, once you crest the 600 lb-ft range, you need to install a torque converter with a billet front cover. Over 800 lb-ft, you need to have not only the billet front cover, but also add in a multi-disc clutch system and steel stator. Over 1400 lb-ft, a custom converter is in order.
What is the most common installation error?
Torque converter not engaged in pump drive.
Despite how it may be called out in the instruction sheet, the most common problem causing transmission failure is not engaging the torque converter on the input shaft. If the torque converter is not fully engaged, the pump will burn out, causing transmission destruction. More often than not, the converter appears to be in place, but the final press to full contact is not made. The converter needs to be spun on the shaft and turned until it reaches correct placement. How will you know? The transmission housing will bolt up easily to the back of the engine. If the transmission requires “pulling into place” by drawing on bolts placed in the bell housing to make it fit, the converter is probably not in the right place. Keep turning the converter and pressing it on the shaft. When it finally hits home you’ll hear that pleasing click of completion.
What do I need to know when calling the tech line for assistance?
There are a number of important specs that are required to ensure the tech line folks can help you select the right parts for your application. It’s a list:
Explain lock up vs. non-lock up transmission – which is right for my street driven car?
A non-lock up converter always has some slippage in the system. This is a common condition in racecars with high stall speed converters, as it allows the power to be delivered to the racetrack in a usable traction-control mode style. Lock up transmissions electronically lock the turbine to the inside cover, giving a solid connection – no slippage. In this case, the turbine is turning at the same rate as the impeller.
As a rule, the tech line folks never recommend non-lock transmissions up for street applications, as non-lock up converters are inefficient for fuel mileage and street performance. Full lock up converters also create less heat and are better for cruising around town.
Electric vs. non-electric transmissions – which is better for me?
It’s a matter of whether you like to be in control of your transmission’s every feature, or not. Simply stated, a traditional non-electronic transmission, such as the GM Turbo 400, will certainly do the job. These transmissions operated through a combination of mechanical parts that would, more often than not, get you close to what you wanted in terms of performance and shifting.
Today’s electronic transmissions such as the 4L80E are plenty strong and will handle most anything you can dish out – plus offer an overdrive gear set for increased fuel mileage. Furthermore, they also offer total control of every feature, including both wide-open throttle and part-throttle shifting points. Those are features you won’t be able to dial in with old school transmissions. They take more time and energy to set up and require the use of some computer system. But if you have the ability to surf the internet with your computer, you have the ability to program one of today’s new electronic transmissions.
Do I need a cooler for my transmission?
In a word, yes. And, make it the biggest transmission oil cooler you can properly install on your vehicle. It should be mounted out of harm’s way, and in an area that has free flowing cool air. Being close to radiator hoses and headers is a big “no no.” This can be especially tough with street rods, but should be considered when designing and building these vehicles.
The Big Stall – how do I find my torque converter stall speed?
This is easy, but often confused. “Foot Stall Speed” is generally an incorrect figure. Placing the transmission in drive while holding the brakes on and noting the engine rpm before the vehicle begins to move is often a better test of brake condition than stall speed. The real number you need is “flash stall” and here is how to get it.
While driving in high gear (with the overdrive switched off if you have one), in a safe area free of traffic and obstructions, quickly depress the throttle. Note the highest rpm shown by the tachometer before the vehicle begins to accelerate. This is your flash stall speed and the number you need when talking to your tech line rep. It’s that simple.
Why can’t I run an 8-inch torque converter in my street car?
Street is not race. There is a difference. The 8-inch racing converters may generate great performance, but they also have high stall speeds, which equate to greater slippage and heat buildup. Generally speaking, the higher the performance of your engine and the hotter the camshaft, the looser the converter (meaning higher stall speed). However, there is a limit, and racing converters in street applications is something to avoid.
My transmission comes with an assortment of rings that allow me to adjust by speedometer – which one is right for me?
Start by counting the number of drive teeth on the transmission gear you are currently using. If you have your rear end gearing ratio and the height of the driving tires in inches, contact the Midwest Converters Help Line (815-229-9808) and we can help you select the right ring for your application.
When should I use a clutchless automatic transmission?
First off, it is not a matter of cost, as the two transmissions have virtually the same cost. Clutchless transmissions are great for circle track competition. They are simpler than transmissions with clutches, requiring fewer lines running through the cockpit and easier installation. Clutchless transmissions use bleed offs to get you going and are a direct lock up system, which does not allow for clutch slippage – and the benefits to efficiency therein. Clutchless transmissions deliver quicker throttle response and immediate application of power making them a good choice if your class of racing allows for this option.
Is an additional oil cooler required with high performance converters?
An additional oil cooler is not required for high performance converters used in typical street or strip applications although added cooling is a good thing. Care should always be exercised when run-up is made at the start line. Any excess time at stall puts the converter at risk due to heat buildup. This type of heat buildup would not be saved with a cooler due to the time involved to get rid of the heat. If a vehicle is to be used in towing, an added cooler is a must. However, for normal use, added cooling is not required. The better the converter is designed, the more efficient it will be and the lower the amount of heat that is generated.
What is Midwest Converters warranty policy?
Conditional lifetime. See our Warranty Policy for more information.