When Pro Stock first started all engines used a 7 lb. per CI weight break. As particular engine combos showed to be quick they were given weight, or allowed to remive weight based on track performance. NHRA did add weight to the 426 Hemi based combos, as they dominated the first couple years of the class. I don't ever recall weekly weight adjustments, but I remember the 426 Hemi based combos ended up getting a lot of weight back off toward the end of the small CI era, and them having the lowest weight per CI factor of 6.4 lbs. per CI.