After finishing his three-day Bondurant class, NASA Arizona driver Cable Rosenberg was filled with that sort of fever that all budding racers have experienced, but no way to express it. A lifelong car nut, he’d already put together a decent-size collection of sports cars, but hadn’t had the chance to explore their performance in a pro-social way. Sadly, his instructors at Bondurant couldn’t point him in a definite direction toward the lowest rung of the racing ladder.
Thankfully, NASA personnel could. His dedicated mechanic, also a NASA instructor, suggested he try NASA HPDE. With that advice in mind, Rosenberg took his first step into motorsports – a short step that morphed into a daring leap. That sort of development, however, would come to define his choice of vehicles in his climb up the Time Trial ladder.
Unwilling to thrash any of his pristine muscle cars while he learned his craft, Rosenberg felt the prudent thing to do was pick up a cheap C4 Corvette as an expendable training tool. While he browsed online listings, he stumbled upon a suitable replacement for a C4: a fully prepped and caged 1997 Viper race car going for $23,000. At that price, he couldn’t say no.
“I think it made me a better driver because, well, those cars were notorious. They have such a massive footprint and a lot of grip, but when mine let go — I was spinning every session the first few times out,” he recalled.
Though not exactly friendly, it was dependable. Every outing was error-free his first year with it, but when the wiring harness melted, Rosenberg took the opportunity to take what he’d learned and see if it translated to a newer, faster, better planted version of the car.
“I also had a 2013 GTS in my garage — a nice street car — and I decided to try in on the track. I never spun that car. It’s got a longer wheelbase and it’s a little wider. The gen five car is all carbon, so the center of gravity’s much lower, and 52 percent rear weight distribution helps with traction. Even with the long engine, it’s packaged well. The front of the engine’s pretty close to the front axle line.”
Svelte Serpent
Rosenberg accepted that the street car couldn’t remain cushy for long if he was going to progress as a driver, so he turned to UMS Tuning to begin a serious diet program. Nearly 400 pounds were pulled from the car by cutting out any unnecessary metal and installing a range of OEM and aftermarket composite parts including the ACR’s carbon rotors. Some of the OEM parts were even reprinted in carbon fiber by Doug Shelby Engineering, including the full undertray formerly made of aluminum.
“We’ve done so many little custom parts. Some of the underbody trays that were aluminum are now carbon fiber,” he begins, “little panels, titanium bolts, you name it — anything to save some weight.”
The final steps were getting the car set up nicely, which they simply borrowed from a proven member of the Viper range. “After we installed proven MCS 2-ways with remote reservoirs, we installed the OEM ACR aero, albeit with an extended splitter by Doug Shelby, then copied the ACR-Extreme’s spring rates, ride height, and rake,” said UMS Tuning’s resident wizard Tony Szirka. “That car had a lot of talented hands in it. I think with the fifth-gen ACR-X, Dodge was committed to making it less of a hammer and more of a stylus,” Szirka added. Those measures amounted to major weight loss: the car now weighs just 2,870 pounds without driver.
That first year of earning his spurs had prepared Rosenberg for the transition into sanctioned competition. Out there anytime there was a NASA event. The group of people with NASA Arizona were friendly enough to help him take the leap into sanctioned competition, but Rosenberg’s application helped him move to the front of the TT1 field quickly. Over the following two years, he’d go on to set six TT1 records in the Arizona Region.
“Once we’d finished the chassis preparation, we were out at the track almost every weekend,” he explained, “It was just so reliable.”
The first iteration of the car was mainly about finding chassis potential. Nevertheless, Rosenberg had purchased a basic 9.0-liter package from Prefix, a large company that mainly prototypes for OEMs and Tier One suppliers, but also has a small team of Viper specialists who have been recognized for their work with normally-aspirated V10s. Of the succession of motors that would go into the car over the following three years, this was by far the mildest.
Mild is a relative term, of course. When used in respect to this 9.0-liter engine, this off-the-shelf Prefix powerplant made roughly 733 horsepower and 686 pound-feet of torque at the wheels.
Scratching the Ceiling
But being the man he is, Rosenberg had to go for more power after some time — after all, there was still plenty of performance ceiling to take advantage of. Rosenberg reached out to Prefix for a race motor that would, in addition to moving him up into Super Unlimited, help him realize the potential of the famous V10.
“We made some valvetrain modifications, increased the compression ratio to 12.5:1, and threw a big cam at it. We didn’t really know what it would make, but it came out to about 800 at the wheels,” said Prefix’s engine maestro Scot Rickord. “The V10 is interesting. It makes its peak torque right around 5,000 rpm regardless of which cam is used.”
In this instance, that peak figure was 698 pound-feet of torque and 803 horsepower. With this setup, the shift point was raised to 7,000 rpm.
Putting that sort of power down in a front-engine rear drive platform was always going to be a bit of a challenge. “At that level, you can’t really use the power in the first three gears,” Rickord added. The factory traction control simply cannot manage the extra power of the engine at this point.
When Rosenberg decided to make the most from this arrangement, he realized keeping both hands on the wheel might help, so, for that reason and a few others, he opted for a 6XD sequential gearbox. Not only would this upgrade help administer the power a little more effectively, it laid the foundation for the next stage of traction control, thereby helping the escalating power output remain manageable.
If they wanted to keep most of the factory functionality with this 6XD six-speed sequential they had planned, they would have to install a MoTeC M150 ECU to allow communication to continue between the CANBUS and all the basic accessories. “Almost everything in the Viper runs on CANBUS — the radio, the displays,” Szirka explained.
Thankfully, the process wasn’t as draining as some might have thought. Due to John Reed’s plug-and-play packages for the MoTeC, the team were spared having to write their own code. His jumper harness and firmware made installation easy, and, vitally, allowed them to retain CANBUS.
With the obvious reduction in shift time, Rosenberg inadvertently set a new TTU record while testing at Chuckwalla.
The MoTeC’s added benefit was its flawless traction setup — one that could easily rein in a much greater power output. As they reached the limits of what was achievable with a 9.0-liter atmospheric engine, this system would prove invaluable.
Four years of reliability ended with one of the roller pins coming off the rocker arms. Rosenberg had been getting a little frustrated witnessing some of the turbo cars in his class leave him on straights, and so he went back to Prefix looking to explore what potential was left in the 9.0-liter setup.
“We tried different bore combinations, three different camshafts, and different piston rings first, then experimented with another intake. The V10, due to the pulses of the extra two cylinders (over a V8), is more sensitive to changes on the intake side. Whatever you do on the exhaust side doesn’t have much of an impact on the output, but the intake does.
“We tried to find an improvement on the OEM three-piece plastic intake, but the Dodge engineers did a great job, not only from an efficiency standpoint, but from a packaging one, too. We had a hard time seeing any notable gains on our side without having to enlarge the intake to the point it would pop out of the hood,” Rickord described.
The experimental iteration of the 9.0-liter motor now made 835 horsepower at the wheels, and the guys at Prefix could say with certainty that they had just about touched the ceiling. “We’d reached what was possible with a sub-six figure engine build,” he added.
Going further would require Prefix move in an unusual direction.
Turbo Time
“If it hadn’t been him, I don’t think we would’ve accepted that job,” Rickord admitted.
Prefix didn’t have much experience turbocharging the V10, but Rosenberg’s request for a mild turbo build seemed sensible enough. “He wasn’t asking for anything crazy — a mild turbo build making north of 1,200 horsepower.”
Rosenberg had picked up another 2013 Viper GTS to dedicate to forced induction, but he reused some parts from the older normally-aspirated motors to build the new force-fed version.
They took the camshaft from his reliable 800-rwhp 9.0-liter build, added an aftermarket crank, their normal rocker arm upgrades, CNC ported heads, a stock block with a closed deck, and – unusual for the team – tried a lower compression ratio. “We believe that a turbo build should rely on the turbo to make the power, so we decided on the 9:1 ratio. I think that’s been a large part of why it’s been able to stay cool enough to run an entire session,” Rickord guessed.
Prefix sent the motor to UMS to install a turbo kit that had to put cooling first. “First off: We weren’t going to build a one-lap wonder,” Szirka added.
EGTs are kept under control thanks in part to using the largest mid-frame turbo Szirka could get his hands on. Twin Garrett G35-1050s with 1.17 A/R are not thought of as responsive in most applications, but having 8.4 liters of displacement to play with wakes these turbochargers up at 2,500 rpm.
Really the main issue has been with packaging. Despite a bathtub-sized engine bay, the intricate piping and additional coolers forced the team to lay the Ron Davis radiator at a 45 degree angle and relocate the ABS module. Because of the limited real estate available, they mounted the Calvo Engineering oil cooler and its three Spal fans behind the differential.
That cooling package means the Viper’s 1,300 horsepower is available from start to finish. Controlling the added power is the MoTeC’s traction system, which works in conjunction with the OEM traction control. The OEM system was useful in the earlier car, but it wasn’t a reliable aid any longer. “The amount of horsepower it can cut is 200 horsepower — a number I calculated when I realized the traction control wasn’t working when dyno-tuning one of the N/A cars,” Szirka said, laughing.
In the context of a turbo build, where 200 horsepower equates to roughly 15 percent of the total output, a second layer of support was needed.
As with the atmospheric motors, exploiting this turbo power is difficult in a front-engine car without a transaxle, but the combination of the ACR aero package and the MoTeC’s sophistication has made it possible to use most, if not all of the power available in gears three and higher. It helps to have the car pointed straight, too. “To floor it, you want the car basically straight. The MoTeC has 10 settings and I’ve got it in the first setting after ‘off.’ I like having it on — I’ll push harder because I believe it might save me.”
Glory Run
The turbo car won’t see NASA competition until 2025, but early testing has been promising. “We don’t want to post any times yet, but the turbo car is nearly 20 mph faster down the front straight at our home track, Podium Club,” Szirka said. That’s encouraging, especially considering the current weight of the car.
“We worried we would have problems with the oil, especially after seeing how the 9.0L’s oil would get up to 260 degrees pretty consistently, but we haven’t had any problems with this motor yet,” Szirka said. “I think having less swept area, a shorter stroke, and less bore that have helped it stay cool.”
There’s still some setup work to do, and the car is quite portly at 3,250 pounds currently. Rosenberg plans to put the turbo car on a diet similar to its predecessor’s at some point soon, and when the car’s ready for SU competition next year, he hopes to snag a new round of trophies to add to his growing collection.
Until then, he has the TT1 hardware to decorate his mantle. “I’ve still got a few TT1 records at tracks that are going to close, so I hope they do that before Kennel can take ‘em from me,” he admits. That competitive spirit is what has driven him all over the country to set staggering lap times, as have his supportive crew of family, friends, and colleagues.
“My wife comes to every event with me. She is my pit crew. We got an RV to make the out-of-state trips more fun, and we love staying overnight at the track. I couldn’t do it without her! I also have to give special thanks to Scot Rickord for all the badass motors over the years, and to UMS Tuning for building a turbo Viper that runs cool. Thanks to Tony Szirka for all his help over the years at the track, and thanks to Tage and Adina Evanson at NASA Arizona for putting on amazing events over the years! I’m looking forward to the next 10!”
