[Dwight Southerland]

w/TH does stand for "with TurboHydramatic". In the case of your '70 Z-28, the car would have been factory equipped with a Turbo 400 which was heavier than the manual transmission. Just for an understanding about the differences in weight, back during the years of most of the Class Guides, manufacturers had to supply relatively accurate shipping weights to freight companies for proper charges of their services. So, depending on the equipment on the car, the "shipping" weights changed. If the car was equipped with V8 engines, air conditioning or disk brakes or other options, the manufacturer calculated the shipping weight to give to the freight companies. The added weights were usually published in AMA (Automobile Manufacturers Association) specifications and you can find examples in those publications. NHRA generally assumed that the racers would use no options cars for competition so the shipping weights were generally the minimums. In the case of the automatic transmission equipped cars, since they would be in classes where the car would be required to have that option, the additional weight was added to the minimum shipping weight for classification. Sometimes the NHRA Classification Guide used the shipping weight differences for calculation and sometimes not.