The racing world is one of constant one-upsmanship. Racers naturally try to one-up the other guys by going faster, driving better…whatever it is. That’s the nature of the beast, and it’s what makes it all so fun and entertaining. The same is true among the parts manufacturers, especially when it comes to the power-adder wars.
In the case of 275 Drag Radial, the two players in the supercharger business are ATI-ProCharger and Vortech, and they are competing against the various turbocharger manufacturers. When it came to the rules regarding the blowers, there were two models accepted: the Vortech Xi and the ProCharger F-1R, as they were produced. A new design of each existing model to be accepted required submitting it for approval to the rules committee. The turbos, however, had clearly defined restrictions that allowed them to work within that structure and do anything they wanted, within reason, to improve their product. It would be deemed legal as long as it met those criteria. In this case, restrictions could work to their advantage.
After the 2011 season, ProCharger sought parity to the turbos and redesigned their F-1R to compete, creating the F-1X, and approached the NMRA rules committee to get it approved. In order to avoid a costly game of one- upsmanship with ProCharger and Vortech, and to create a set of supercharger guidelines (like the turbos have) so that both companies were on the same page, the NMRA’s Charlie Harmon and Trey Capps had a conference call with both companies to hash out what these guidelines should be. The result was a set of rules that both the F-1X and the new Vortech XB105 met.
Any single commercially available centrifugal racing supercharger permitted that fits the following criteria: Volute housing Inlet diameter—external OD 5” maximum, housing inducer bore inside diameter 4.20” maximum, impeller wheel exducer diameter 6.00” maximum, discharge diameter—external discharge diameter 3.5” maximum, housing diameter (greatest external diameter of housing not to include discharge)—11.0” maximum. Impeller wheel and housing may not be stepped, clipped or notched. Housing must maintain a continuous contour feature from the housing inducer bore to the exducer outlet. Super Chargers with a 4.1 or larger inch volute inducer bore ID must add 75lbs to base weight. Multi-staged supercharged induction systems are prohibited.
To meet these rules, Vortech updated its Xi-trim with a new billet compressor wheel and a re-machined housing. The housing is the same as the Xi, with the exception of the inducer being opened up to the rules-approved 4.2 inches (the Xi is 4.085 inches) and minor machining inside to match the new billet wheel. Other than a slightly different adapter plate to mate the compressor side to the gearbox, it’s the same supercharger as the Xi. One feature that has been teased but not fully developed at press time is the supercharger’s “tunable diffusion” capabilities that allow the supercharger to be tailored to a particular engine combination and rpm. Vortech won’t divulge any more than that, so it should be interesting to see how that works.
As we go to press, the only person we know of that has any testing data on the XB105 blower is Chip Provenza, who recently ran the eighth-mile at Maryland International Raceway, and the results were impressive. He said, “It makes at least 7 psi more than the Xi. I say ‘at least’ because I run a 3-bar map sensor and it pegged it. It makes well over 30 in the eighth-mile, and made 30.1 psi by 8,000 rpm. The high- est reading on the sensor was 30.7.” That translates into roughly 6 mph in the quarter, based on Provenza’s estimate.
“In first gear, you had to be at the top of your shift point before the Xi made its full boost, and then it flat-lined and wouldn’t make any more. This blower, it seems like the higher you run it the more boost it makes. I’m ecstatic with it.”
The new V-24 XB105 is available as a complete unit (part no. 2G348-150) for $4,600.95, or as an upgrade to an existing Xi-Trim (part no. 00100195) for $1,999.95.