S.P.A.X. is using the classing system that SCCA uses for all their solo events. We are an independent club with no SCCA affiliations. This is just a classing system in order to get accurate PAX times for each driver.
PAX works similarly to a golf handicap: You may be in a stock grocery getter and someone else in a full-spec race car.
To make it more fair, the race car's time will be multiplied by the so called PAX index (the handicap) and may result in an overall time, that gives the stock car a chance. Class your car here: