The ProCharged 572 cubic-inch engine that Pro Line Racing is building for Project BlownZ28 is going to crank out some serious horsepower, so that means it will need a stout transmission and torque converter behind it. To make sure all of the horsepower is put to the ground reliably and efficiently we selected ATI’s three-speed Max Duty Outlaw T400 transmission and a Neal Chance Racing Converters billet NXS torque converter for the job.
In this article, Rob Sappe and John Lane from ATI provide some great information as to why you want to use a heavy-duty transmission for an application like this. We also spoke with Marty Chance from Neal Chance Racing Converters about what you need to look for when selecting a torque converter if you’re running a high-horsepower supercharged combination.
The ATI Max Duty Outlaw T400 Transmission
With almost 60 years of experience building high-performance driveline parts, ATI knows what needs to go into a transmission like the Max Duty Outlaw T400. The particular unit it sent for BlownZ28 has a 1.51 First and 1.26 Second-gear six-pinon gearset, increased clutch capacity, a high-flow Super Pump, billet aluminum valve body with clean neutral, a 300M HD output shaft, and other high-end parts. Everything is housed inside an ATI SuperCase that’s designed to work with the 1.125-inch main shaft and has a Chevy-style bellhousing so it can bolt up to the Dart-based block. Information about the rest of the transmission’s parts can be found right here on ATI’s website.
So, why exactly were all of these parts used in the transmission? Sappe explained what ATI’s thought process was when it came to selecting parts for the Max Duty Outlaw T400.
“This transmission includes the maximum number of race lined clutches and high-grade steels that can be installed in its custom drums, which greatly increases the torque holding capability. The 1.60 low gearset is a six-pinion design versus a four pinion OEM design and is also made from high-grade material. By using a 1.60 gear versus an OEM 2.48 gear, this allows the car to hook on marginal tracks with big power and a small tire. The input, main shaft, and output shaft are all manufactured from high-grade materials that can withstand large torque loads. The input and main shaft are also larger in diameter than OEM, as well.”
The SuperCase is another key feature of the Max Duty Outlaw T400 necessary for this build. The SFI 4.1 rated case is made of 356-T6 cast aluminum, so it doesn’t require any additional shielding. It also has more center support lugs that give second gear additional strength. This case can also deal with higher line pressures, and ATI has removed unused passages so it has a quicker transbrake release than a stock-style case.
Two-Speed vs. Three-Speed And Why You Need A Tough Transmission
There’s a lot of options available when it comes to selecting a transmission for a racecar, and you have to make sure the one you choose works the best with your application. You have to take into account things like vehicle weight, horsepower, the RPM range you’ll be operating in, the camshaft, the torque converter, drive tires, and the style of racing you’re doing.
With a high horsepower build the large input shaft is recommended when you’re in our Max Duty line of transmissions. – John Lane, ATI
Lane explained the benefits and differences in a two- or three-speed transmission for racing use.
“You need to make sure the available gear ratio will match the power versus the weight of the car. High-winding cars that are lightweight would naturally want a three-speed transmission, but from the stock ratio of a 2.48 to a 1.48 might be too large of an RPM drop and suck the wind out of the engine. This is where you would look at a closer ratio to keep the engine up in the powerband. A two-speed transmission is used in small-tire racing and limited traction situations. The two-speed shines once you get to the point of needing less than a 1.51 First gear. It also works well when limiting the power isn’t enough and the starting line ratio must be dropped.”
When you get into the category of high-horsepower applications it changes some of the parts you’ll want to use. We’ve already outlined in this article what some of those parts are, but you also need to consider other options for this type of transmission. The different types of dump options to manipulate transmission line pressure and torque converter pressure are going to be two things you need to think about. You also need to ensure the gearset is absolutely correct for your application.
“With a high-horsepower build, the large input shaft is recommended when you’re in our Max Duty line of transmissions. The upgrade isn’t that expensive and it’s worth the investment for the added protection and ability to grow into more horsepower. We typically recommend this shaft for vehicles that have a big-block and weigh over 3,000 pounds, or have a small-block and weigh over 3,200 pounds,” Lane said.
Torque Converter Selection
A supercharged combination like the one we’re using in BlownZ28 must have the right torque converter bolted to the engine or it will struggle to get down the track. The converter needs to be tuned for maximum efficiency and properly load the engine for an optimal rate of acceleration. BlownZ28 is going to be making Pro Modified-level power, but will be riding on a 275 radial, so that will impact how the converter is tuned.
We want to maximize the power transfer — that’s what the converter is, it’s a power transfer unit. -Marty Chance, Neal Chance Racing Converters
After looking at the engine and supercharger package of BlownZ28, Marty Chance explained why he recommended the NXS converter.
“The top-end of this engine says it’s going to have a broader torque band than the average HEMI engine. It’s going to need to be loaded at a faster rate, but another parameter is that this will be on a 275 Pro Drag Radial, not a 36-inch tall Top Fuel slick. So, you’ll want this aggressive converter for the power curve of the engine, but we have a power limit because of the tire. To solve this, we soften the converter via a stator design that takes the aggression away from the tire, so at the hit when you release the transbrake it gives you what we call a ‘bigger window of margin’ so it doesn’t knock the tire off.”
By going this route with the converter it will give our team a better tuning window with the converter so they can get it dialed-in quicker.
“The way you want to tune a converter is to look at the right information, and the most important information is power transfer. When you dyno a vehicle, the horsepower number you see will be lower than what the engine is actually producing because of the efficiency losses in the driveline, so we want to minimize those losses as much as possible. We want to maximize the power transfer — that’s what the converter is, it’s a power transfer unit,” Chance says.
The NXS Converter
One of the things that Neal Chance Racing Converters prides itself on is the research and development of its converters. The company spends an immense amount of time designing its parts, but it also spends just as much time testing these parts at the track to make sure they’re perfect when customers receive them. By taking the time to really understand what a supercharged engine likes in terms of power application, Neal Chance found the recipe to create the NXS torque converter.
“The NXS is a converter that has a split blade pump impeller. What that means is on the vacuum side, or low-pressure side of the pump impeller, we’ve intentionally weakened it by shortening every other blade. What that does is it weakens the initial coupling force of the converter so that at the shock load it spikes slippage into the converter, which allows us to throw power at it and control the tire by initially slipping the converter momentarily. To compensate for that we’ve put more blades on the high-pressure side. For example, a normal converter would have around 30 blades on the pump impeller, an NXS has 40 blades on the high-pressure side,” Chance explains.
How does this NXS technology apply to a car like BlownZ28? According to Chance, it comes down to having maximum control over the tire.
“The reason that can be an advantage in small-tire racing is that it lets us use a very aggressive converter that softens at the hit. This allows us to throw more power at it, and control the aggression to the tire by softening the hit when we weaken the low-pressure side of the pump impeller. That way we’re not overpowering the tire in those crucial first few feet of the track during a run.”
The ATI Max Duty Outlaw T400 transmission and Neal Chance Racing Converters NXS torque converter are the perfect match for Project BlownZ28. It’s going to be exciting to see how well these parts work with that big Pro Line Racing Engines mill and the ProCharger supercharger. Make sure you follow the entire BlownZ28 build right here on Dragzine as the car gets closer to being track ready!