The torque converter is a magical device – it takes the force provided by your engine’s combustion process and turns it into usable power that can be routed through an automatic transmission to drive the wheels, thus propelling your car forward with a minimum of muss and fuss.
In practice, the torque converter is a fluid coupling that acts much like a clutch does in a manual transmission-equipped car. As more power is applied through the engine, the converter spins harder, using the force applied to the fluid to transfer that power effectively with a minimum of power loss. But torque converter manufacturing has always been thought of as a black art – comparably, there are few successful aftermarket companies who build racing converters when factored against the number of companies who build racing transmissions.
One of those companies is Neal Chance Racing Converters, which boasts a very successful track record with their torque converters in all types of racing applications. The company’s roots trace all the way back to big-brother Mitch Chance and Marty cutting open torque converters in their father’s transmission shop when Marty was in high school.
We talked with Neal Chance to learn how to engineer a proper torque converter for a small-tire combination.
Many classes are now campaigned on a 275-wide drag radial tire, which is one of the more difficult combinations to harness on the track. You need to be able to stick the tire on the launch, multiply enough torque to get the heavy car moving, and then have the torque converter maximized as much as possible heading downtrack.
NCRC’s Marty Chance was eager to get talking with us on converter development, and suggested one of the company’s NXS Full Billet racing converters that has been custom-engineered for our application.
Neal Chance’s NXS line of converters is the result of the company’s thirty-plus months of research and development into what makes a torque converter work properly in a supercharged application and offers a number of significant advances that have proven to show gains on the track.
For example, they’ve got a number of Pro Modified doorslammers turning in their quickest elapsed times ever, with 60-foot times in the sub-.900-second range.
The Technology Inside
The Origins Of The NXS Design
“This converter concept is something that we developed a few years ago that has absolutely taken over the Blown Alcohol world. We saw evidence of areas that could be better. For example, when we would make a converter very efficient, we noticed that at the top of high gear, when we got past a certain percentage, the G-meter would drop off much quicker than it should in many different applications.”
“Also, we know that when we design a converter for a given application, in a non-lockup version, that converter has to be a compromise converter – it’s tighter on the launch than we really want to be so that we can maintain the efficiency we need out the back. You need to let the engine speed free up, let the engine get happy, and bring the driveshaft to it.”
“That’s the recipe for making your car as quick and fast as it can possibly be,” says Chance.
Neal Chance’s full line of NXS torque converters are constructed from proprietary billet aluminum using a variety of different alloys developed by the engineers at Alcoa.
Even the two separate halves of the converter are made from different types of aluminum that are specifically formulated for the forces those components will see during a typical dragstrip pass.
“You have incredible hydraulic forces, radial forces, and heat cycles acting on the converter every time you go down the track – the aluminum has to live through hundreds and hundreds of heat cycles. You heat it up, and you’ve got hydraulic forces inside the converter producing thousands of pounds per square inch of pressure,” says Chance.
For example, think about what occurs during the dreaded tire shake – something you have to contend with on some drag-radial-equipped cars. The hydraulic power transmission is being turned on and off like a paint shaker, except the paint shaker is your high horsepower car.
The tire shake is basically turning the horsepower on an off through the entire drivetrain – including the torque converter. As a result, the converter needs to be able to handle the on-and-off power transfer, during a heat cycle, while the hydraulic pressure inside is trying to blow the converter apart.
Tire shake is strong enough to crack chassis welds and break wheelie bars, thus, you can see how important the engineering process is in relation to torque converters.
The design of the converter shell and internal components have been developed by the NCRC on-site engineering staff and are cut from those billets on Chance’s five-axis CNC machinery. Internal components include the NCRC Extreme Duty Monster Mechanical Diode and heavy-duty thrust bearings that are designed to stand up to the incredible shock loads transmitted through the drivetrain.
A variety of stator designs are available in fabricated steel, CNC billet steel, or CNC billet aluminum.
The pump hub is hardened, and the entire assembly is both internally and externally balanced for the ultimate in smooth operation. They’ve even got a CNC-machined billet titanium option for those racers who must have the absolute lightest, strongest converter that money can buy – and as you might imagine, it’s probably not wise to look at the checkbook before ordering one.
All of these items come together to produce a torque converter that is 12 to 20 pounds lighter than other bolt-together torque converter designs, and even six pounds lighter than Chance’s own aluminum/steel bolt-together design. Removing rotating weight is always an advantage in a drag racing application, and this is just one of the places where the Chance NXS design shines.
The number one difference between the NCRC NXS torque converter and other designs on the market today is that the NXS converter is built from scratch, every single time, for the particular application where it will be used. Each one starts as a solid block of aluminum and ends up as a torque converter that’s been specifically designed for a performance application – not one that’s built from a repurposed core.
On The Line
When the transbrake is released, a torque converter needs to apply the engine’s power to the transmission, and subsequently to the ground.
The NXS converter design has a number of enhancements to enable the user to do so, but we were only able to get Chance to tell us a few of the secrets to how the converter operates.
“At the hit, this converter will be smoother than any clutch or other converter design has been in the past. As the engine speed comes up, the NXS design will drive the tire harder, so in essence, it’s got the best of both worlds. It’s almost looser on the front half and tighter on the back side. Before, it was either one or the other, and you didn’t get both. If you made it tighter, it was tighter everywhere, and if you loosened it up, it was looser everywhere,” Chance explains.
NCRC doesn’t just build torque converters and send them out into the wild for testing, though, and in fact, Marty has tested the NXS design on his own X275 car that runs a short-stroke, high-RPM ProCharger F-1R-boosted engine. “We built a little bitty 8-inch NXS converter that stalled at 8,100 RPM, launched it off the transbrake at 5,800 RPM, and it didn’t even try to take the front tire off the ground…it was that smooth,” he says.
Tuning And Data Acquisition
“The number one rule to make the engine happy is to avoid not getting zero slippage – slippage is what makes you fast. Nobody runs a triple-disc instant-lockup clutch, they run a triple-disc slipper clutch. Slippage makes the motor happy, and making the motor happy is the fastest way to accelerate your car,” Chance explains.
Our NXS technology has proven to be the fastest thing you can put behind a supercharged engine. – Marty Chance
To bring that into perspective, the affordability of computer tuning and data acquisition have brought the torque converter into the 21st century. Without the data acquisition of nearly every parameter that has become prevalent over the last decade, recent advances in torque converter technology would not have been possible.
The intent of a top-shelf torque converter is to develop a rate of efficiency that will allow the powerplant to accelerate the mass of the car at its quickest possible rate, and that’s why Chance feels that every converter needs to be tailored to each particular vehicle – because no two cars are exactly the same.
Another item that’s critical to converter operation is tuning once the converter has been installed, as that’s one of the advantages to using the bolt-together design. There’s a reason that big-time racing operations always have a full-time clutch guy on the staff, and that’s because there’s always something left on the table.
A racer needs to be constantly tuning on the torque converter in order to run at the front of the pack, because the same theory applies. It’s only as good as the work put into it, no matter how advanced the design is.
As you can see, choosing a torque converter for a top-flight racing effort shouldn’t be as easy as picking a part number from a list. It’s an involved process that takes many factors into account, chief among them the powerplant’s operating conditions (1/8th or 1/4-mile) and others like transmission gear ratios, rearend gear ratios, vehicle weight, camshaft specifications, how much boost or nitrous will be used for the application, and more.
One particular item Chance touched on during our conversation changed how we think about torque converters. He asked, “When people judge a converter through the data, what’s the first thing they do? They open the log and go straight to the finish line — they want to know what the slippage is at the finish line. But is there anything on a race car – any component – that you tune from the finish line back to the starting line? Not the fuel system, not the suspension, the blower, the turbo, or the nitrous, so why would you look at a converter that way? You tune from the starting line. The efficiency of the converter is relative to the acceleration – the back half will take care of itself if you make the front half accelerate.”
Torque converters have well and truly taken over in drag racing, and as such, they’ve become one of the most quickly-evolving technologies in our sport. With not just one, but a handful of new converters launched over the last year, the Neal Chance team has shown a strong commitment to not only competing, but keeping its customers at the forefront of racing, and the numbers have certainly done the talking.