This article contains everything you need to know about selecting the correct torque converter for your vehicle's automatic transmission in 2015.
1) The Way Torque Converters Work
2) What is the impeller
3) What does stall speed mean?
4) How to choose the right torque converter for your automatic tranmission
5) What to expect from a high performance torque converter
6) What Kind of engine do you have or are you building?
7) Matching Gear Ratios
8) Torque Converter Sizing
9) Getting the Right Fit
How to choose the right torque converter for your vehicle
It is critical that you select the right type of converter and stall for vehicle. Not only torque converters for the race track but also on the street. The right converter can be the sole factor between winning and losing a race or the performance of your vehicle on the street but choosing the best torque converter for your vehicle application can be tough. Here are some basic guidelines that can help you find the right converter for your specific application.
Your torque output and power curve are the two main factors you should focus on when selecting a torque converter. Take a look at stall speed for instance, if your stall is rated at 2200 to 2700 RPM, it means it is rated to cover a variety of engine and transmissions with different power curves. For the best performance you want to choose a stall that is somewhere near the peak torque of the engine in question. Engines with more low-end toque usually increase stall speed. The exact same converter used on an engine with lower RPMs will stall.
Another thing to consider is the resistance put on the engine. Heavier cars with big boy tires will create more work for the transmission. If you have more resistance on the engine and transmission you want to have a higher stall RPM. It's the same principles used in gear ratios. A heavier car with tall gears will have higher stall RPMs then a light car with short gears and small tires.
To recap: The most important things to consider when choosing a torque converter is the engine displacement, vehicle weight, cam profile, tire diameter, type of fuel system used in the vehicle, the type of automatic transmission year and model, and compression ratios.
The way torque converters work
Manual transmissions don't use a torque converters the way that automatic transmissions do. Manual transmissions use a clutch to connect the engine power to the automatic transmission. In an automatic transmission, it's the torque converters job to transmit and maximize the engines power to the wheels. For more information about automatic transmissions, check out our post titled "How automatic transmissions work?". If you took a torque converter apart you would find three major components: The slator, impeller and turbine. For more infomation about torque converters, check out the post "Everything you need to know about torque converters explained".
What is the impeller?
The impeller pump rotates at engine speed and is located on the transmission side. As your RPMs increase, flowing of fluid increases inside the torque converter. The power is transferred by using fins and vanes that direct the fluid flow in the direction of the turbine. The turbine is connected to the flexplate. In between the turbine and impeller is the slator. The slator functions as a type of one way clutch that changes the direction of the fluid and maximized the torque power output. When the power of the fluid flow increases enough, the turbine begins to spin or spline in the transmission onto the input shaft. The torque converter characteristics are controlled by the number and shape of fins, the diameter and slator design.
What does stall speed mean?
Stall speed refers to the amount of RPMs the engine is able to reach with the transmission in gear and the brakes locked before the drive wheels start to turn. Stall speeds are a great way to rate torque converters performance level. The range level will tell you a lot about what to expect from the torque converter. In you select a 2700-3000 converter, it should be able to footbrake stall the torque converter to about 2700 rpm considering the automobile setup.
Typically this would increase your RPMs from a dead stop by 500-1500, giving you a significant increase in vehicle acceleration. Super Chevy posted, "When discussing torque converter stall speed, there are two different terms: "Rated Stall" (it's common for enthusiasts to call this "foot brake stall") and "Flash Speed." What's the difference? Foot brake stall is just that. You load the converter by stomping one foot on the brakes and the other on the gas. Watch the tach. The rpm at which the converter overpowers the brakes is simply the "foot brake stall."
"Flash speed," on the other hand, is quite different. Flash occurs the instant you release the foot brake and the rotating inertia (which is "stored" in the engine flexplate) is released. In many cases, this flash speed can be anywhere from 500-2,500 rpm higher than the foot brake stall speed. In the case of a race car, a drag racer will stage at idle, hold the brakes, and "flash" the converter (flooring the gas pedal) the instant the last yellow on the Tree comes on. The same technique can be used with a street car to increase the engine rpm level when the car leaves a stop light."
What to expect from a high performance torque converter
All of Road Runner's high performance torque converters are engineered to provide durability and strength. These converters are designed with heavy-duty internals and high ware bearings, you can expect a long life out of these converters and a huge increase in performance over OEM torque converters or factory made torque converters.
Torque converters can be difficult to understand because there are so many factors involved in the choosing the right one. Many people end up selecting the wrong type of converter for their vehicle resulting in poor automobile performance.
This doesn't have to be the case for you though. You can learn how to choose the right torque converter by following this guide. You will learned how to match a converter to rear axle ratios and cam size, learn about stall speed and converters for engines with nitrous and blowers.
What Kind of engine do you have or are you building?
You need to start thinking about what type of engine (Straight/ Inline Engines, V Type Engines, Boxer/ Flat Engines, Wankel/ Rotary Engines, Diesel Engines) you are installing the torque converter on before even starting your search. For street converters, you need to make sure and match midrange and low engine toque to the torque converters stall speed. For instance, if your building a small block street engine that uses most of its torque around 2500 - 3500 RPMs, don't get a torque converter that stalls at 4000. Not only will the converter slip and be destroyed but the car will be hard to drive. Also don't get a converter that's too small If you are driving a big block engine that makes its torque around 4500 and you select a converter with stalls at 4000, don't expect it to be a fun ride on the street due to high stalls and rear axle gear locking up to the converter.
Selecting camshafts are almost just as important and selecting torque converters. For street camshafts, most people just choose a cam that will make the RPM range of the engine 1500-2000 PRMs higher than the stock camshaft. This will reduce your bottom end toque peak so you might need a higher stall converter to match the new torque. Don't do like most people and select the recommended converter but not upgrade your wheel axle to work with the higher stall speed.
For example if you build a v8 small block with a a 235 degree (at .050)/.488 in. lift cam and added a torque converter rated at 3-3500 RPM. To make it all work together properly with a small amount of converter slippage you would want at least a 4.10 rear axle gear with 26-27 in. tires.
If you vehicle has nitrous oxide or a supercharger, that also effect torque converter selection. Engines with added power produce more torque. Normally stock engines aren't made to withstand that much toque.
In order to get the best performance out of your supercharged engine, you want to select a torque converter with a low stall speed range. If your torque converter stalls to high it could cause it to slip and eventually destroy itself do to too much heat.
Matching Gear Ratios
Tire diameter and real axle gear ratios are very important when selecting torque converters. You converter needs to function at full lockup at cruising speeds also referred to as the final cruse rpm (your rpm generated based on rear axle gear ration and tire diameter). Not doing this could cause your converter to slip constantly. Trap speed will let you know if the torque converter is efficiently operating when going through traps. Usually, 100 rpm of converter slippage equals a loss of one and a half miles per hour through the traps.
Trap speed rpm will tell you if the converter is operating efficiently when going through the traps. Typically, 100 rpm of torque converter slippage equates to a loss of 1 1/2 mph through the traps.
Torque Converter Sizing
Torque converter sizing can be pretty confusing. Converters usually range from eleven to twelve inches in diameter all the way down the lowest, 7 inches. The smaller the torque converter you have, the lower amount of fluid that has to get pumped through it. The lower amount of fluid you have the less drag that is being created on the internal of the converter, which lets it stall at higher speeds. Thats why 8-10 inch torque converters are rated for racing vehicle applications. You want to try to avoid small torque converters on street cars due to the high stall speeds usually around 3000 RPMs and up.
If your vehicle is using nitrous(over 200 hp) or running a blower (above 12 psi), or are using a trans-brake, you will want a torque converters that is made to handle the extra power and stresses they will put on the engine. The extra power generated from those additions will cause your converter to expand in diameter or "balloon". You will need a torque converter with high quality slators and anti ballooning plates to keep them from expanding.
Vaugn from the Chevy Talk forum said, "An anti-balloning plate is used on torque convertors that have a high-input torque - like on diesels or big blocks.
A torque convertor is a fluid clutch - think of two fans pointed at each other, one turned on and the other not powered. The "not-powered" fan will tend to spin up to NEARLY the speed of the powered fan, but not quite. The "not-powered" fan will be hooked to the transmission input, the powered fan will be hooked to the motor in this example.
Now incase the two fans inside a torque convertor shell, and fill it with fluid.
When the fans are submerged in fluid (and one is powered by an engine), they will generate a LOT of hydraulic force - enough force to cause the torque convertor's metal case to literally stretch - or balloon up. So, your convertor's anti-ballooning plate resists this tendency for the torque convertor to "balloon".
It is EXTREMELY common for diesel trucks with automatic transmissions to blow up torque convertors, because diesel motors have so much torque in them. IF a standard torque convertor is used in a diesel truck or big block equipped truck without the ballooning plate installed on it, it will regularly destroy torque convertors."
It helps to know this information below when selecting the type of torque converter that is perfect for your transmission:
- Stroke & Bore
- Cylinder Head Types
- Lobe Centerline, Cam Lift and Duration at .050 inch
- Manifold and Carburetor
- Ratio of Compression
- Primary Header Tube Diameter (How to select primary header tube diameter)
Vehicle weight tells the manufacturer of the converter how much work in required to get a certain elapsed time. It also affects the gear ratios and assists in indicating what converter flash rpm can remain effective and still be used.
Body style also affects the calculation of gear ratio/horsepower. It might need to be adjusted if the front of your vehicle is large. This will give the converter manufacturer an idea of the amount of air the vehicle is pushing.
Getting the Right Fit
One of the biggest complaints about selecting torque converters is that they don't fit. Often a brand new torque converter seems like it will not fit the input shaft on the transmission. That's because the new converters are built to closer specifications and will fit tighter. Just because the converter wont slip on easy doesn't mean it won't fit, it just might need a little more effort get it on there.
A great way to make sure your new converter fits properly is to compare the two. Three ways to tell if your torque converters match. You should measure the overall length, depth of the hub slot and the inside diameter of the hub slot. Make sure that before you remove the own converter, check the dimensions by looking at the bell housing on the front. This will also help you install your new torque converter properly.
Other things about torque converters to consider
A torque converter with a higher stall will make extra stress where it couples with the engine, so make sure and use SFI approved flexplates and quality torque converter bolts. Flexplates made for Chevys are typically double drilled for large and small bolt patters, removing the guessing game out of the equation.
Torque converters created for aftermarket application comes neutrally balanced and are usually designed for internally balanced engines. Usually externally balanced engines the balance weight is on the flexplate but on Chryslers-240 /360 small block the balance is put on the torque converters. Make sure and get the correct counterweighted flexplate if you happen to have one of these engines. Typically, almost all SPI approved Chrysler flexplates already have the counterweight.
You can study for days about torque converters or you can get advice from a true professional like the ones at Road Runner Converters. Give us a call today or view our large selection of high performance torque converters, ford transmission torque converters, street converters and towing converters. Welcome to Roadrunner Converters Blog. Roadrunner was founded in 1979 with high quality torque converters for sale as our primary goal in mind. Our philosophy has always been "we believe in being better". Our focus on quality has been the reason for out phenomenal growth and customer loyalty.
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