Modern Torque Converter Tech With Circle-D Specialties

There’s little doubt that technology over the years has played a huge part in the automotive industry. Cars and trucks have become more efficient and they stay on the roads longer. In years past two-speed units were the standard offering, but today we see 10-speeds as the new normal. As the transmission has evolved, the torque converter had to follow suit. While we know that they have changed, we weren’t sure in what ways or the specific areas.

To find out the latest in the torque converter innovation, we reached out to Chris Sehorn, owner of Circle-D Specialties. The company specializes in performance converters for transmissions from two-speeds to 10, covering GM, Ford, and Dodge units, and has been building them for years. 

Converter Technology Over The Years

So, what’s changed in torque converter design? 

“The most significant variance in these transmissions and the converters used is the lockup feature,” Chris begins. “The Powerglide, Turbo 350/400, and C4 transmissions are a traditional non-lockup. In any of these transmissions, the converter is essentially a fluid coupling design that uses a turbine, pump and a stator. An early lockup-style transmission was initially built for efficiency. There’s a clutch inside the torque converter that is activated by fluid pressure that can be controlled by a solenoid.”

Unlike previous lockups, the new units will begin to apply the clutches slowly and not fully to help the converter couple. 

In the older transmissions with a lockup, the lockup is only enabled in fourth gear. This action, when engaged, locks the converter to the input shaft by activating a clutch in the converter which doesn’t allow any slip, increases fuel mileage while reducing transmission temperatures. However, with today’s modern advancements, this is no longer the case. Chris explains, “The newer model transmissions will start locking up as early as second gear. Unlike previous lockups, the new units will begin to apply the clutches slowly and not fully to help the converter couple. This action will keep the converter efficient, and by third or fourth gear, it will completely lock. At this point, you’re not even using the hydraulic side of the converter anymore.”

 Multi-Disc Clutches

By now, you have probably heard of multi-disc clutches being used in converters. And like us, you may be wondering if they will wear out like a clutch in a manual transmission over time.  

Chris said, “Typically, a wet clutch will last longer than a dry one. Tuning plays a massive role in the lockup. When tuned correctly, the clutches in a converter will last the life of a vehicle. But you do not want to overly increase the apply pressure because this will cause the clutch material to fail prematurely. The increase in pressure can also cause the converter to balloon, distorting the lockup apply surface. This is why a billet front cover is so essential in a traditional converter. The billet front cover dramatically stiffens up the lockup area to prevent any flexing when power is applied.”

So now that we know how the clutch in a torque converter operates, why do some units have multiple clutches and others just a single? 

“This mainly depends on the engine’s torque level. A lockup clutch has a specific torque capacity. The factors that determine its capability are the coefficient of friction, inside diameter of the lockup surface, outside diameter of the lockup surface, force applied to the piston, and cone angle (10L90).” Chris continues, “The torque capacity is multiplied by the number of clutch surfaces. So if a single disc will handle your torque level, there is no reason for a multi-disc.” But don’t worry, Circle-D offers one, three, and five-disc clutch packs with its converters, depending on what your needs are.

Our latest in stator design comes from our engineering department using Computational Fluid Dynamics (CFD). 

The Stator

The stator is a finned device that lives in the center of the torque converter, and its design directly affects the efficiency and stall speeds. The stator’s job is to redirect the transmission fluid from the turbine back to the pump, which causes torque multiplication. As you can imagine, with new technology and state-of-the-art machinery, stators have changed over the years, as well. 

“Stator technology has improved from using OE stators to full five-axis CNC machined billet stators. Utilizing the multitude of OE options on our 245mm, 258mm, and 265mm platforms, we can target different torque curves and power levels to achieve exceptional performance,” Chris explains. “We have learned a lot over the last 10 years by trial and error, and we can dial-in a setup. Our latest in stator design comes from our engineering department using Computational Fluid Dynamics (CFD).” 

Modern Torque Converter Design

Even though Circle-D Specialties has been building high-performance torque converters for some time, in 2018, the company invested in CFD software. This software will be revolutionary for Circle-D by helping it design new parts. It will not only help develop products for new transmissions, but it will also allow them to take a look at older units like the Powerglide to see areas they can improve upon. Chris explains, “We are really just on the tip of the iceberg with this software, since we’ve only been using it for about a year and a half. But, it’s already allowed us to design stators and converters without ever having to test them in cars.”

CFD software is not a new concept — companies like General Motors and Ford have been using it for years. Incredibly, more and more aftermarket companies like Circle-D can use this type of tool for virtual tuning. The days of building a one-off part, testing it, and then making changes before going to market are gone for some. This process not only saves money in research and development, but it also cuts down the time it takes to get a new part to market. Chris shares an example, “We can take a look with the software and apply certain theories to see where the pressures are too low or too high. We can even see where the fluid is as the converter starts to couple. It will even calculate torque multiplication for you, and it applies to all two- to 10-speed transmissions.”

At the time of this article, Circle-D had only used the CFD software for the development of the 10-speed torque converters. However, it is planning on revisiting all of its convertors from the eight-speeds all the way down to the two-speed units, because the company thinks it can get better torque multiplication using the software. 

“In theory, CFD allows us to control the torque multiplication a little more. We can hit areas hard, and it will show us what the number is. The current method of trial and error in our industry is fading, and being able to see a simulated converter run is insightful as well as amazing. It’s going to be a game-changer,” Chris says.

Here is a look at what the Computational Fluid Dynamics (CFD) software looks like in action. According to the Circle-D Specialties team, this program is changing the way torque converters are built and tested.

This software could very well take Circle-D to the next level, too. Ultimately it could open up options of not only better torque multiplication, but better fuel economy as well as drivability.

As of right now, Circle-D is shipping out the GM and Ford 10-speed torque converters as fast as they can make them. Even though these units are done, they are never really finished. Chris explains, “The first iteration is complete, but we will continue to work on the design. I’m pretty positive that we will be able to get more aggressive in areas, especially on the naturally -aspirated (N/A) versions of the converters.”

Concave Converters For The 10l80e

If you’ve seen a torque converter for one of the 10-speed transmissions, you will notice that they look much different than a 4l60e or any other overdrive converter. This revolutionary design from GM utilizes what it calls Integrated Torque Converter (iTC).

You can see here that the 10-speed torque converter has a unique concave design that is not common with traditional converters.

“By switching to an ITC design, you remove the lockup piston, thus shortening the overall length of the converter and reducing rotating mass. The clutch bond and apply surface are angled, with the bond surface also having a slight concave radius to it.” Chris continues, “This angled concave approach allows the clutch to form to the apply surface much better than the standard flat-style clutch. When you’re calculating the torque capacity, there are two design methods: uniform pressure theory, and uniform wear theory. Think of uniform pressure as a new clutch, and uniform wear as a used clutch. Rigid pistons move towards the uniform wear at a much faster rate than the flexible pistons. A uniform pressure theory allows for a smaller OD/ID ratio. Our current theory is this new concave piston shape is designed to flex and form to the lockup surface. This allows the iTC to follow more of the uniform pressure theory. The angled surfaces provide a cone-style lockup, also increasing the holding capacity compared to the traditional flat style. It’s an ingenious design, and kudos to the engineers who thought this one up.”   

In this image, you can see the angled cone-style lockup clutch which increases the holding capacity when compared to a traditional flat style.

Torque Converter Maintenance

Another area of interest that we asked about is converter maintenance. We were curious about what to look for and signs that could show you a problem. Chris said, “There’s not a lot you can do as far as maintenance goes with a converter, especially if it’s a lockup type. We offer a bolt-together with our non-lockup, but even then, you’re still limited.”

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,” Chris explains. “I like to see older transmissions in the 160- to 180-degree range. The newer transmission will be around 180- to 200-degrees. Anything over 200-degrees is a cause for concern.” 

And, according to Chris, if you have a 6L80E, don’t be surprised if you see temperatures over 200-degrees from the factory. Even with the OEM torque converter and transmission cooler, these units like to run hot. Surprisingly, 200- to 210-degrees is a standard operating temperature for them.

Who Can Benefit?

If you’re a performance enthusiast trying to get more from your vehicle, then you need a performance converter. The factory, whether it be Ford, GM or Dodge, mass produces torque converters and is not always overly concerned with performance. They do care about how fast they can get them off the assembly line and a couple of other things. Chris explains, “It’s not that the factory torque converters won’t handle added horsepower, because they will — we have seen some of them live up to 750 horsepower. They’re just not designed for performance. Instead, they build them for fuel economy and so that the average driver will not be annoyed by the feel of a performance unit.”

Left: RPM Motorsports A10 Camaro ZL1, know as Frostbite has gone an​ 8.65 at 160.54 mph with the help of Circle-D Specialties. Right: Chase Lautenbach of Street Car Takeover has run a best of 8.57 at 163 mph as well with a 10-speed transmission and a Circle-D converter.

If you take a stock 12-inch converter out of a car and replace it with a 10- or even an 11-inch unit, it’s going to be faster. Chris told us that even with a bone-stock engine, a converter change is going to result in better performance, especially with the 60-foot times.

Ordering The Right Converter

If you’re in the market for a torque convertor, don’t just run out and buy what you think you need. Bigger is not always better. Instead, the Circle-D team advises that you give them a call, email, or even send them a text. They also have a form on the website, so there’s no reason you can’t reach them.

“We like to get as much information out of our clients as possible before recommending a product. We want to know the intent of use — is it a daily-driver, street toy, track queen? From there, we will look at the expected torque curve — is the engine naturally-aspirated, nitrous, turbocharged, or supercharged? We will also want to know the cam specs, gearing, and vehicle weight. All of these elements play a critical role when selecting the proper torque converter.”

While choosing the perfect torque converter for your car might seem overwhelming, Circle-D does its best to ease the process. It has a knowledgeable staff that can answer any torque converter questions or concerns that you may have and get you exactly what you need.

Article Sources

About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
Read My Articles

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