The nitrous-injected Pro Modifieds are knocking on the door of the five-second zone and the IHRA has adjusted their rules to get them there quicker. In a statement issued today, the IHRA's technical department has reduced the minimum weight for the nitrous cars by 25 pounds. The nitrous-injected Pro Modifieds are knocking on the door of the five-second zone and the IHRA has adjusted their rules to get them there quicker. In a statement issued today, the IHRA's technical department has reduced the minimum weight for the nitrous cars by 25 pounds.