Written by Jason Reiss
Photography by FSC Archives/Tara Bowker/Courtesy of the Manufacturers
For many years, the Pro Mod eliminator enjoyed three main options for extra-atmospheric vehicle propulsion: superchargers, nitrous oxide injection, and turbochargers—with the latter two choices mostly self-explanatory. Until recently, blown combinations were mostly centered around Hemi engines topped off with either a roots- or screw-style supercharger. However, the inclusion of centrifugal superchargers into NMCA VP Racing Fuels Xtreme Pro Mod—and the Pro Mod classes of other series with the exception of NHRA at this time—opened the door for mainstream centrifugal supercharger companies like ProCharger and Vortech to enter one of the hottest classes in modern drag racing.
In the VP Racing Fuels Xtreme Pro Mod class, small-block centrifugal-supercharged combinations can weigh 2,250 pounds, while 5.0-inch bore-space, big-block combinations are a little heavier at 2,425 pounds and are used as the benchmark with adders and deducts for other configurations. For example, cars with engines using the traditional 4.84-inch bore spacing can deduct 75 pounds, and an extra 100 pounds is added to those cars running 5.3-inch bore-space engines.
Eric Dillard of Pro Line Racing has much to share on the topic of building engines for this combination, as the company has been at the forefront of development for the Galot Motorsports-backed cars of Kevin Rivenbark and John Strickland. Rivenbark shocked the world earlier this year at the Sweet 16 2.0 race held at South Georgia Motorsports Park, carding a 3.587 at 206.67mph pass with an engine that is extremely similar to—yet different from—one used in traditional Pro Mod competition.
“These engines are 548 cubic inches instead of the Pro Mod-legal 520s, and they have outlaw valves instead of legal valves, but it still gives them some kind of representation of what it’s going to do at 2,600 pounds on the same track in the same conditions,” Dillard explains.
Interestingly, this whole concept of centrifugal superchargers in Pro Mod started with the Radial vs. The World program of one James Lawrence, who just so happens to have been the co-founder/former part owner of RacePagesDigital.com/NMCA parent company ProMedia Publishing. Although Lawrence is no longer involved, his influence still reverberates as a result of this program.
“James wanted us to get connected with ProCharger for his Radial vs. the World car in December of 2016 at PRI; it took all of 2017 to build his car, and then this all started to come together in 2018,” Dillard said.
The ProCharger-boosted Hemi engine deployed in Lawrence’s car is identical to those used in Rivenbark and Strickland’s cars. In fact, Dillard says that the Pro Line design team tried a number of different camshafts before coming back to the identical package from Lawrence’s engine.
“The combination right off the bat was really refined and close. Since then we’ve learned how to tune and power-manage the car, and had blower development from ProCharger continuing to work on their product,” Dillard elaborated.
A new raised-cam block from Alan Johnson Performance Engineering allowed for even more development to take place; just one week prior to talking with us, Dillard says the engine combination powered to a 3.69 at 203 mph in PDRA Pro Boost trim (564 cubic-inch engine) in high 80-degree weather and 3,500 feet density altitude.
Compressors from ProCharger and Vortech
As with any racing class, creating parity is up to the rules makers, and creating products that cause them to seek parity is up to the parts manufacturers. Both ProCharger and Vortech manufacture multiple compressors that are currently in use under the hoods of several racecars. ProCharger’s offerings include the F-3R-136 and the F-3X-140, while Vortech offers the V-30 131A, V-30 131B, and newly designed V-30 132A.
“We’ve had guys on the fringe of running Pro Mod for quite a few years, but nobody who’s really been competitive. Even though our F-3R 136 has been out there for quite a while and capable of 3,000 horsepower-plus, it took the right combination and the right people with the right motivation to get out there and do it,” Walt Sipp, Technical Service Manager, ProCharger, said.
“Our setup, in particular, is a lot simpler when it comes to the tuning aspect of it, so once you have a good converter program under your belt, and a good chassis and suspension package, it’s all in getting the car to 60-foot.”
By that he means that the turbocharged Pro Mod combinations might make 4,500 horsepower, and the centrifugal-supercharged cars might make 3,500 or somewhere in that neighborhood. But it comes down to getting the mass moving, and the consistency of the centrifugal-style superchargers helps immensely in this regard.
“For instance, when you saw Rivenbark run .911 or .920 60-foot on average at the Sweet 16 event, there isn’t a turbo car that going to be able to do that. That’s where we’re at with it—we can out 60-foot and out-330 them and still make enough power to stay in front of them at the big end,” Sipp said.
There is a large difference in eighth-mile trap speed between the three different types of cars in the Pro Mod class. The snail cars typically carry around an extra 10 mph across the stripe, while the nitrous cars are just a few mph slower than the centrifugal cars. The nitrous cars are a little bit lighter than the centrifugal cars, but Sipp says it’s all relative.
“You can make all the power in the world, but if you can’t turn it on until the very end, and the other guy made a better lap than you, you’re not going to catch him,” he added.
There are several transmission-and-converter combinations in use at this time on these types of cars, from the tried-and-true three-speed Turbo 400 transmission with lockup converter to five-speed Liberty transmissions, but Sipp says the three-speed is the only real ideal combination for quarter-mile, NHRA-style Pro Mod racing.
Vortech Superchargers is currently working specifically with Terry Leggett in PDRA Pro Boost to develop its new Pro Mod-style centrifugal supercharger and expand its V-30 line of centrifugal race superchargers further into the Pro Mod market.
Initially, Leggett was competing with one of Vortech’s V-30 131A superchargers—and doing well, to the tune of mid-3.70s at over 200 mph in the eighth-mile—but has since moved to an experimental 132mm compressor stage, according to Vortech’s Lance Keck.
He explains that Vortech has a deliberate plan in place to develop this product using a new, top-secret computational fluid dynamics software to model the performance of the compressor and its capabilities. Since implementing this into its development process, the company has seen immense gains in the performance of the supercharger.
But it didn’t come easy. Working in conjunction with Leggett and longtime engine builder Charlie Buck of Buck Racing Engines, they had to revisit the capabilities of Leggett’s tried-and-true, 526 cubic-inch Alan Johnson Hemi to allow it to suck down the 4,000-plus cubic feet per minute of airflow and 45-plus pounds of boost coming from the supercharger.
“The roots and screw-type superchargers make full boost in half a second and maintain the same boost curve throughout the run. Our centrifugal will continue to make more boost depending on the rpm of the motor,” Keck explained. “This allows the centrifugal to make the maximum amount of power the track and car can handle at any given time, which translates into a much easier car to tune and for the driver to get it down the track quicker.”
“We had to modify the induction system to work best where the supercharger is most efficient. Developing a new camshaft profile is part of the picture, and we also had to raise the dynamic compression through mechanical means to maximize performance, among other things.”
Those “other things” he’s referring to are the improvements made to the supercharger’s impeller profile—they’ve discovered several advancements through the use of the CFD program that have spurred changed in the impeller and housing design.
Keck says the combination is capable of well over 3,000 horsepower and climbing, and it’s due to the improvements they’ve been able to make to the supercharger’s efficiency range through the use of the software program. The V-30 gearcase is plenty strong to handle the power of the compressor side, and at this point they are fine-tuning the specifics of the supercharger before moving forward. Eventually, he says, the supercharger will also likely find a home in Radial vs. The World competition, with a derivative appearing in the Limited Drag Radial class.
There are pluses and minuses to every combination used in Pro Mod; the boosted cars do well in the spring and fall when the density altitude provides dense air and cool temperatures, while the nitrous-injected cars tend to shine in the heat of the summer when the centrifugal-boosted engines don’t have the same efficiency as they do at the bookends of the season.
Proper Tuning Matters
“When the air gets bad, that’s when the challenge kicks in for the centrifugal cars. When you have a transmission and the inefficiencies that go along with that, it’s the nature of the beast. Bad air magnifies your problem,” Jason Lee, tuner extraordinaire at Part Time Performance Racing, said. “To get the blower sped up or the engine sped up, you may have to change gear ratios or loosen the converter to free the blower and the engine up. Both of those items become inefficient in bad air, which compounds the problem and makes the car difficult to run. But a centrifugal car in spring and fall, when the air’s good, they can even the playing field because they become more efficient.”
Lee cautions that once the engine tune is correct, there’s not much more to be gained in the sense that advancing the timing won’t really pick up any power on a properly tuned engine. The only options to alter performance in these combinations are the aforementioned gear changes and converter adjustments, and just throwing more supercharger speed into the equation is not necessarily the answer to more performance.
Sipp agrees wholeheartedly.
“You can’t make a rules package in March in good air on a sticky track. You’ve gotta think about how it’s going to play out throughout the season. How a nitrous car and a turbo car and a blower car react on a good track versus dead heat of the summer when the track’s sketchy and it’s 100 degrees outside, they’re all going to react differently. You have to look at the season as a whole; you can’t beat the guys up because the race car drivers aren’t the ones who prep the track or control the weather,” he said.
“The supercharger has its sweet spot; you have to manage the RPM through the ratios to achieve what you’re trying to do. It’s very difficult to do when conditions are not optimal. But when the air gets good that same combination revs much faster, accelerates much harder and the blower gets to max RPM much faster,” Lee said. “As a result of all of those things, the car’s flying and you’re extremely competitive. The centrifugal supercharger is one of the most consistent combinations that there is. If you leave at the same RPM in the same air, you’re always going to leave at the same boost. You can manage your tune-up around that, knowing that’s a constant.”
The cars tested during the NHRA U.S. Nationals with mixed results. The plan was to give NHRA a starting point for the combination, but only Galot Motorsports’ John Strickland managed to dig into the 5-second zone with a 5.88 in his Pro Line-powered Camaro, with Clint Hairston driving the Elite Motorsports ProCharger-boosted Camaro to a 6.00 elapsed time. Of course there is still work to be done—both by the racers wanting to use the combination, and the NHRA to accept it—but the groundwork has been laid.
For 2020, the NHRA has taken over the Pro Mod class from the Real Pro Mod Association, so after hearing about the efforts put together by some of the most prominent performance companies on Earth to put centrifugal superchargers into the winner’s circle in Pro Mod, we have no doubt that the class—and NMCA Xtreme Pro Mod, along with RvW by extension—will be the home of a supercharger renaissance. It’s only a matter of time.
Part Time Performance
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Pro Line Racing Engines
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